| 1. |
- Gardeström, Per, 1950-
(författare)
-
METABOLITE LEVELS IN THE CHLOROPLAST AND EXTRACHLOROPLAST COMPARTMENTS OF BARLEY LEAF PROTOPLASTS DURING THE INITIAL PHASE OF PHOTOSYNTHETIC INDUCTION
- 1993
-
Ingår i: Biochimica et Biophysica Acta. - : Elsevier BV. - 0006-3002 .- 1878-2434 .- 0005-2728. ; 1183:2, s. 327-332
-
Tidskriftsartikel (refereegranskat)abstract
- Metabolite levels were determined in the chloroplast and extrachloroplast compartments of barley protoplasts during photosynthetic induction using rapid fractionation by membrane filtration. This method allowed studies with a high time resolution the first determination of subcellular metabolite content bring made after only 0.3 s. Upon illumination, dark-adapted protoplasts exhibited a 1 min lag phase prior to commencement of oxygen evolution, and the maximum rate was reached after 4 to 5 min. In contrast to oxygen evolution, the ATP/ADP ratio in the chloroplasts increased from 1 to 2 within 0.5 s and reached a maximum of about 5 after 2 s. There was a dramatic increase in the extrachloroplastic ATP/ADP ratio within a few seconds, reaching a maximum after about 15 s. During the initial phase of photosynthetic induction, the subcellular ATP/ADP ratios were very similar in photorespiratory (low CO,) and non-photorespiratory (high CO,) conditions. The ATP/ADP ratios in both the chloroplast and extrachloroplast compartments remained high until photosynthetic oxygen evolution started and then decreased when the photosynthetic rate reached its maximum. In steady-state photosynthesis the subcellular ATP/ADP ratios were considerably higher under photorespiratory conditions as compared to non-photorespiratory conditions. During the initial phase of photosynthetic induction, 3-phosphoglycerate decreased and triose phosphates increased both in the chloroplast and extrachloroplast compartments. The changes in these metabolites are consistent with a 3-phosphoglycerate/triose phosphate shuttle using the phosphate translocator as the means to supply ATP to the cytosol during photosynthetic induction.
|
|
| 2. |
|
|
| 3. |
|
|
| 4. |
- Althage, Magnus, et al.
(författare)
-
Cross-linking of transmembrane helices in proton-translocating nicotinamide nucleotide transhydrogenase from Escherichia coli: implications for the structure and function of the membrane domain.
- 2004
-
Ingår i: Biochimica et biophysica acta. - : Elsevier BV. - 0006-3002 .- 0005-2728. ; 1659:1, s. 73-82
-
Tidskriftsartikel (refereegranskat)abstract
- Proton-pumping nicotinamide nucleotide transhydrogenase from Escherichia coli contains an alpha and a beta subunit of 54 and 49 kDa, respectively, and is made up of three domains. Domain I (dI) and III (dIII) are hydrophilic and contain the NAD(H)- and NADP(H)-binding sites, respectively, whereas the hydrophobic domain II (dII) contains 13 transmembrane alpha-helices and harbours the proton channel. Using a cysteine-free transhydrogenase, the organization of dII and helix-helix distances were investigated by the introduction of one or two cysteines in helix-helix loops on the periplasmic side. Mutants were subsequently cross-linked in the absence and presence of diamide and the bifunctional maleimide cross-linker o-PDM (6 A), and visualized by SDS-PAGE. In the alpha(2)beta(2) tetramer, alphabeta cross-links were obtained with the alphaG476C-betaS2C, alphaG476C-betaT54C and alphaG476C-betaS183C double mutants. Significant alphaalpha cross-links were obtained with the alphaG476C single mutant in the loop connecting helix 3 and 4, whereas betabeta cross-links were obtained with the betaS2C, betaT54C and betaS183C single mutants in the beginning of helix 6, the loop between helix 7 and 8 and the loop connecting helix 11 and 12, respectively. In a model based on 13 mutants, the interface between the alpha and beta subunits in the dimer is lined along an axis formed by helices 3 and 4 from the alpha subunit and helices 6, 7 and 8 from the beta subunit. In addition, helices 2 and 4 in the alpha subunit together with helices 6 and 12 in the beta subunit interact with their counterparts in the alpha(2)beta(2) tetramer. Each beta subunit in the alpha(2)beta(2) tetramer was concluded to contain a proton channel composed of the highly conserved helices 9, 10, 13 and 14.
|
|
| 5. |
|
|
| 6. |
- Boudière, Laurence, et al.
(författare)
-
Glycerolipids in photosynthesis : composition, synthesis and trafficking.
- 2014
-
Ingår i: Biochimica et Biophysica Acta. - : Elsevier BV. - 0006-3002 .- 1878-2434 .- 0005-2728. ; 1837:4, s. 470-80
-
Tidskriftsartikel (refereegranskat)abstract
- Glycerolipids constituting the matrix of photosynthetic membranes, from cyanobacteria to chloroplasts of eukaryotic cells, comprise monogalactosyldiacylglycerol, digalactosyldiacylglycerol, sulfoquinovosyldiacylglycerol and phosphatidylglycerol. This review covers our current knowledge on the structural and functional features of these lipids in various cellular models, from prokaryotes to eukaryotes. Their relative proportions in thylakoid membranes result from highly regulated and compartmentalized metabolic pathways, with a cooperation, in the case of eukaryotes, of non-plastidic compartments. This review also focuses on the role of each of these thylakoid glycerolipids in stabilizing protein complexes of the photosynthetic machinery, which might be one of the reasons for their fascinating conservation in the course of evolution. This article is part of a Special Issue entitled: Dynamic and ultrastructure of bioenergetic membranes and their components.
|
|
| 7. |
- Bratic, I, et al.
(författare)
-
Mitochondrial energy metabolism and ageing
- 2010
-
Ingår i: Biochimica et biophysica acta. - : Elsevier BV. - 0006-3002 .- 0005-2728. ; 1797:6-7, s. 961-967
-
Tidskriftsartikel (refereegranskat)
|
|
| 8. |
- Brzezinski, Peter, et al.
(författare)
-
Variable proton-pumping stoichiometry in structural variants of cytochrome c oxidase
- 2010
-
Ingår i: Biochimica et Biophysica Acta. - : Elsevier BV. - 0006-3002 .- 1878-2434 .- 0005-2728. ; 1797:6-7, s. 710-23
-
Tidskriftsartikel (refereegranskat)abstract
- Cytochrome c oxidase is a multisubunit membrane-bound enzyme, which catalyzes oxidation of four molecules of cytochrome c2+ and reduction of molecular oxygen to water. The electrons are taken from one side of the membrane while the protons are taken from the other side. This topographical arrangement results in a charge separation that is equivalent to moving one positive charge across the membrane for each electron transferred to O2. In this reaction part of the free energy available from O2 reduction is conserved in the form of an electrochemical proton gradient. In addition, part of the free energy is used to pump on average one proton across the membrane per electron transferred to O2. Our understanding of the molecular design of the machinery that couples O2 reduction to proton pumping in oxidases has greatly benefited from studies of so called "uncoupled" structural variants of the oxidases. In these uncoupled oxidases the catalytic O2-reduction reaction may display the same rates as in the wild-type CytcO, yet the electron/proton transfer to O2 is not linked to proton pumping. One striking feature of all uncoupled variants studied to date is that the (apparent) pKa of a Glu residue, located deeply within a proton pathway, is either increased or decreased (from 9.4 in the wild-type oxidase). The altered pKa presumably reflects changes in the local structural environment of the residue and because the Glu residue is found near the catalytic site as well as near a putative exit pathway for pumped protons these changes are presumably important for controlling the rates and trajectories of the proton transfer. In this paper we summarize data obtained from studies of uncoupled structural oxidase variants and present a hypothesis that in quantitative terms offers a link between structural changes, modulation of the apparent pKa and uncoupling of proton pumping from O2 reduction.
|
|
| 9. |
|
|
| 10. |
- Conlan, Brendon, et al.
(författare)
-
Photo-catalytic oxidation of a di-nuclear manganese centre in an engineered bacterioferritin 'reaction centre'
- 2009
-
Ingår i: Biochimica et Biophysica Acta. - : Elsevier. - 0006-3002 .- 1878-2434 .- 0005-2728 .- 1879-2650. ; 1787:9, s. 1112-1121
-
Tidskriftsartikel (refereegranskat)abstract
- Photosynthesis involves the conversion of light into chemical energy through a series of electron transfer reactions within membrane-bound pigment/protein complexes. The Photosystem II (PSII) complex in plants, algae and cyanobacteria catalyse the oxidation of water to molecular O(2). The complexity of PSII has thus far limited attempts to chemically replicate its function. Here we introduce a reverse engineering approach to build a simple, light-driven photo-catalyst based on the organization and function of the donor side of the PSII reaction centre. We have used bacterioferritin (BFR) (cytochrome b1) from Escherichia coli as the protein scaffold since it has several, inherently useful design features for engineering light-driven electron transport. Among these are: (i.) a di-iron binding site; (ii.) a potentially redox-active tyrosine residue; and (iii.) the ability to dimerise and form an inter-protein heme binding pocket within electron tunnelling distance of the di-iron binding site. Upon replacing the heme with the photoactive zinc-chlorin e(6) (ZnCe(6)) molecule and the di-iron binding site with two manganese ions, we show that the two Mn ions bind as a weakly coupled di-nuclear Mn(2)(II,II) centre, and that ZnCe(6) binds in stoichiometric amounts of 1:2 with respect to the dimeric form of BFR. Upon illumination the bound ZnCe(6) initiates electron transfer, followed by oxidation of the di-nuclear Mn centre possibly via one of the inherent tyrosine residues in the vicinity of the Mn cluster. The light dependent loss of the Mn(II) EPR signals and the formation of low field parallel mode Mn EPR signals are attributed to the formation of Mn(III) species. The formation of the Mn(III) is concomitant with consumption of oxygen. Our model is the first artificial reaction centre developed for the photo-catalytic oxidation of a di-metal site within a protein matrix which potentially mimics WOC photo-assembly.
|
|
| 11. |
|
|
| 12. |
|
|
| 13. |
|
|
| 14. |
|
|
| 15. |
- Friederich, Malou, et al.
(författare)
-
Diabetes-induced up-regulation of uncoupling protein-2 results in increased mitochondrial uncoupling in kidney proximal tubular cells
- 2008
-
Ingår i: Biochimica et Biophysica Acta. - : Elsevier BV. - 0006-3002 .- 1878-2434 .- 0005-2728. ; 1777:7-8, s. 935-940
-
Tidskriftsartikel (refereegranskat)abstract
- We have previously reported increased O(2) consumption unrelated to active transport by tubular cells and up-regulated mitochondrial uncoupling protein (UCP)-2 expressions in diabetic kidneys. It is presently unknown if the increased UCP-2 levels in the diabetic kidney results in mitochondrial uncoupling and increased O(2) consumption, which we therefore investigated in this study. The presence of UCP-2 in proximal tubular cells was confirmed by immunohistochemistry and found to be increased (western blot) in homogenized tissue and isolated mitochondria from kidney cortex of diabetic rats. Isolated proximal tubular cells had increased total and ouabain-insensitive O(2) consumption compared to controls. Isolated mitochondria from diabetic animals displayed increased glutamate-stimulated O(2) consumption (in the absence of ADP and during inhibition of the ATP-synthase by oligomycin) compared to controls. Guanosine diphosphate, an UCP inhibitor, and bovine serum albumin which removes fatty acids that are essential for UCP-2 uncoupling activity, independently prevented the increased glutamate-stimulated O(2) consumption in mitochondria from diabetic animals. In conclusion, diabetic rats have increased mitochondrial UCP-2 expression in renal proximal tubular cells, which results in mitochondrial uncoupling and increased O(2) consumption. This mechanism may be protective against diabetes-induced oxidative stress, but will increase O(2) usage. The subsequently reduced O(2) availability may contribute to diabetes-induced progressive kidney damage.
|
|
| 16. |
|
|
| 17. |
- Gelzinis, Andrius, et al.
(författare)
-
Mapping energy transfer channels in fucoxanthin-chlorophyll protein complex.
- 2015
-
Ingår i: Biochimica et Biophysica Acta. - : Elsevier BV. - 0006-3002 .- 0005-2728. ; 1847:2, s. 241-247
-
Tidskriftsartikel (refereegranskat)abstract
- Fucoxanthin-chlorophyll protein (FCP) is the key molecular complex performing the light-harvesting function in diatoms, which, being a major group of algae, are responsible for up to one quarter of the total primary production on Earth. These photosynthetic organisms contain an unusually large amount of the carotenoid fucoxanthin, which absorbs the light in the blue-green spectral region and transfers the captured excitation energy to the FCP-bound chlorophylls. Due to the large number of fucoxanthins, the excitation energy transfer cascades in these complexes are particularly tangled. In this work we present the two-color two-dimensional electronic spectroscopy experiments on FCP. Analysis of the data using the modified decay associated spectra permits a detailed mapping of the excitation frequency dependent energy transfer flow with a femtosecond time resolution.
|
|
| 18. |
- Glaser, Elzbieta, et al.
(författare)
-
The organellar peptidasome, PreP : a journey from Arabidopsis to Alzheimer's disease
- 2010
-
Ingår i: Biochimica et Biophysica Acta. - : Elsevier BV. - 0006-3002 .- 1878-2434 .- 0005-2728. ; 1797:6-7, s. 1076-1080
-
Tidskriftsartikel (refereegranskat)abstract
- The novel peptidasome, called presequence protease, PreP, was originally identified and characterized in Arabidopsis thaliana as a mitochondrial matrix and chloroplast stroma localized metalloprotease. PreP has a function as the organellar peptide clearing protease and is responsible for degrading free targeting peptides and also other unstructured peptides up to 65 amino acid residues that might be toxic to organellar functions. PreP contains an inverted Zn-binding motif and belongs to the pitrilysin protease family. The crystal structure of AtPreP refined at 2.1 A demonstrated a unique totally enclosed large cavity of 10000 A3 that opens and closes in response to peptide binding, revealing a novel catalytic mechanism for proteolysis. Homologues of PreP have been found in yeast and human mitochondria. Interestingly, the human PreP, hPreP, is the protease that is responsible for clearing the human brain mitochondria from the toxic amyloid-beta peptide (Abeta) associated with Alzheimer's disease (AD). Accumulation of Abeta has been shown in the brain mitochondria from AD patients and mutant transgenic mice overexpressing Abeta. Here, we present a review of our present knowledge on structural and functional characteristics of PreP and discuss its mitochondrial Abeta-degrading activity in the human brain mitochondria in relation to AD.
|
|
| 19. |
|
|
| 20. |
- Havelius, Kajsa G. V., et al.
(författare)
-
The formation of the split EPR signal from the S-3 state of Photosystem II does not involve primary charge separation
- 2011
-
Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - : Elsevier BV. - 0005-2728 .- 1879-2650 .- 0006-3002 .- 1878-2434. ; 1807:1, s. 11-21
-
Tidskriftsartikel (refereegranskat)abstract
- Metalloradical EPR signals have been found in intact Photosystem II at cryogenic temperatures. They reflect the light-driven formation of the tyrosine Z radical (Y-z(center dot)) in magnetic interaction with the CaMn4 cluster in a particular S state. These so-called split EPR signals, induced at cryogenic temperatures, provide means to study the otherwise transient Y-z(center dot) and to probe the S states with EPR spectroscopy. In the S-0 and S-1 states, the respective split signals are induced by illumination of the sample in the visible light range only. In the S-3 state the split EPR signal is induced irrespective of illumination wavelength within the entire 415-900 nm range (visible and near-IR region) [Su, J. H., Havelius, K. G. V., Ho, F. M., Han, G., Mamedov, F., and Styring, S. (2007) Biochemistry 46. 10703-10712]. An important question is whether a single mechanism can explain the induction of the Split S-3 signal across the entire wavelength range or whether wavelength-dependent mechanisms are required. In this paper we confirm that the Y-z(center dot) radical formation in the S-1 state, reflected in the Split S-1 signal, is driven by P680-centered charge separation. The situation in the S-3 state is different. In Photosystem II centers with pre-reduced quinone A (Q(A)), where the P680-centered charge separation is blocked, the Split S-3 EPR signal could still be induced in the majority of the Photosystem II centers using both visible and NIR (830 nm) light. This shows that P680-centered charge separation is not involved. The amount of oxidized electron donors and reduced electron acceptors (Q(A)(-)) was well correlated after visible light illumination at cryogenic temperatures in the S-1 state. This was not the case in the S-3 state, where the Split S-3 EPR signal was formed in the majority of the centers in a pathway other than P680-centered charge separation. Instead, we propose that one mechanism exists over the entire wavelength interval to drive the formation of the Split S-3 signal. The origin for this, probably involving excitation of one of the Mn ions in the CaMn4 cluster in Photosystem II, is discussed.
|
|
| 21. |
- Huang, Yafei, et al.
(författare)
-
Substrate binding and the catalytic reactions in cbb3-type oxidases : the lipid membrane modulates ligand binding
- 2010
-
Ingår i: Biochimica et Biophysica Acta. - : Elsevier BV. - 0006-3002 .- 1878-2434 .- 0005-2728. ; 1797:6-7, s. 724-31
-
Tidskriftsartikel (refereegranskat)abstract
- Heme-copper oxidases (HCuOs) are the terminal components of the respiratory chain in the mitochondrial membrane or the cell membrane in many bacteria. These enzymes reduce oxygen to water and use the free energy from this reaction to maintain a proton-motive force across the membrane in which they are embedded. The heme-copper oxidases of the cbb3-type are only found in bacteria, often pathogenic ones since they have a low Km for O2, enabling the bacteria to colonize semi-anoxic environments. Cbb3-type (C) oxidases are highly divergent from the mitochondrial-like aa3-type (A) oxidases, and within the heme-copper oxidase family, cbb3 is the closest relative to the most divergent member, the bacterial nitric oxide reductase (NOR). Nitric oxide reductases reduce NO to N2O without coupling the reaction to the generation of any electrochemical proton gradient. The significant structural differences between A- and C-type heme-copper oxidases are manifested in the lack in cbb3 of most of the amino acids found to be important for proton pumping in the A-type, as well as in the different binding characteristics of ligands such as CO, O2 and NO. Investigations of the reasons for these differences at a molecular level have provided insights into the mechanism of O2 and NO reduction as well as the proton-pumping mechanism in all heme-copper oxidases. In this paper, we discuss results from these studies with the focus on the relationship between proton transfer and ligand binding and reduction. In addition, we present new data, which show that CO binding to one of the c-type hemes of CcoP is modulated by protein-lipid interactions in the membrane. These results show that the heme c-CO binding can be used as a probe of protein-membrane interactions in cbb3 oxidases, and possible physiological consequences for this behavior are discussed.
|
|
| 22. |
- Ivanov, Alexander G, et al.
(författare)
-
The induction of CP43' by iron-stress in Synechococcus sp. PCC 7942 is associated with carotenoid accumulation and enhanced fatty acid unsaturation.
- 2007
-
Ingår i: Biochimica et Biophysica Acta. - : Elsevier BV. - 0006-3002 .- 0005-2728. ; 1767:6, s. 807-13
-
Tidskriftsartikel (refereegranskat)abstract
- Comparative lipid analysis demonstrated reduced amount of PG (50%) and lower ratio of MGDG/DGDG in iron-stressed Synechococcus sp. PCC 7942 cells compared to cells grown under iron sufficient conditions. In parallel, the monoenoic (C:1) fatty acids in MGDG, DGDG and PG increased from 46.8%, 43.7% and 45.6%, respectively in control cells to 51.6%, 48.8% and 48.7%, respectively in iron-stressed cells. This suggests increased membrane dynamics, which may facilitate the diffusion of PQ and keep the PQ pool in relatively more oxidized state in iron-stressed compared to control cells. This was confirmed by chlorophyll fluorescence and thermoluminescence measurements. Analysis of carotenoid composition demonstrated that the induction of isiA (CP43′) protein in response to iron stress is accompanied by significant increase of the relative abundance of all carotenoids. The quantity of carotenoids calculated on a Chl basis increased differentially with nostoxanthin, cryptoxanthin, zeaxanthin and β-carotene showing 2.6-, 3.1-, 1.9- and 1.9-fold increases, respectively, while the relative amount of caloxanthin was increased only by 30%. HPLC analyses of the pigment composition of Chl–protein complexes separated by non-denaturating SDS-PAGE demonstrated even higher relative carotenoids content, especially of cryptoxanthin, in trimer and monomer PSI Chl–protein complexes co-migrating with CP43′ from iron-stressed cells than in PSI complexes from control cells where CP43′ is not present. This implies a carotenoid-binding role for the CP43′ protein which supports our previous suggestion for effective energy quenching and photoprotective role of CP43′ protein in cyanobacteria under iron stress.
|
|
| 23. |
- Jensen, Poul Erik, et al.
(författare)
-
Structure, function and regulation of plant photosystem I.
- 2007
-
Ingår i: Biochimica et Biophysica Acta. - : Elsevier BV. - 0006-3002 .- 0005-2728. ; 1767:5, s. 335-52
-
Tidskriftsartikel (refereegranskat)abstract
- Photosystem I (PSI) is a multisubunit protein complex located in the thylakoid membranes of green plants and algae, where it initiates one of the first steps of solar energy conversion by light-driven electron transport. In this review, we discuss recent progress on several topics related to the functioning of the PSI complex, like the protein composition of the complex in the plant Arabidopsis thaliana, the function of these subunits and the mechanism by which nuclear-encoded subunits can be inserted into or transported through the thylakoid membrane. Furthermore, the structure of the native PSI complex in several oxygenic photosynthetic organisms and the role of the chlorophylls and carotenoids in the antenna complexes in light harvesting and photoprotection are reviewed. The special role of the ‘red’ chlorophylls (chlorophyll molecules that absorb at longer wavelength than the primary electron donor P700) is assessed. The physiology and mechanism of the association of the major light-harvesting complex of photosystem II (LHCII) with PSI during short term adaptation to changes in light quality and quantity is discussed in functional and structural terms. The mechanism of excitation energy transfer between the chlorophylls and the mechanism of primary charge separation is outlined and discussed. Finally, a number of regulatory processes like acclimatory responses and retrograde signalling is reviewed with respect to function of the thylakoid membrane. We finish this review by shortly discussing the perspectives for future research on PSI.
|
|
| 24. |
|
|
| 25. |
- Lewin, Anna, et al.
(författare)
-
Heme a synthase in bacteria depends on one pair of cysteinyls for activity.
- 2016
-
Ingår i: Biochimica et Biophysica Acta. - : Elsevier BV. - 0006-3002 .- 0005-2728. ; 1857:2, s. 160-168
-
Tidskriftsartikel (refereegranskat)abstract
- Heme A is a prosthetic group unique for cytochrome a-type respiratory oxidases in mammals, plants and many microorganisms. The poorly understood integral membrane protein heme A synthase catalyzes the synthesis of heme A from heme O. In bacteria, but not in mitochondria, this enzyme contains one or two pairs of cysteine residues that are present in predicted hydrophilic polypeptide loops on the extracytoplasmic side of the membrane. We used heme A synthase from the eubacterium Bacillus subtilis and the hyperthermophilic archeon Aeropyrum pernix to investigate the functional role of these cysteine residues. Results with B. subtilis amino acid substituted proteins indicated the pair of cysteine residues in the loop connecting transmembrane segments I and II as being essential for catalysis but not required for binding of the enzyme substrate, heme O. Experiments with isolated A. pernix and B. subtilis heme A synthase demonstrated that a disulfide bond can form between the cysteine residues in the same loop and also between loops showing close proximity of the two loops in the folded enzyme protein. Based on the findings we propose a classification scheme for the four discrete types of heme A synthase found so far in different organisms and propose that essential cysteinyls mediate transfer of reducing equivalents required for the oxygen-dependent catalysis of heme A synthesis from heme O.
|
|
| 26. |
|
|
| 27. |
- Pedersen, Anders, 1976, et al.
(författare)
-
Titration of E. coli transhydrogenase domain III with bound NADP+ or NADPH studied by NMR reveals no pH-dependent conformational change in the physiological pH range.
- 2005
-
Ingår i: Biochimica et biophysica acta. - : Elsevier BV. - 0006-3002 .- 0005-2728. ; 1707:2-3, s. 254-8
-
Tidskriftsartikel (refereegranskat)abstract
- A pH-titration 2D NMR study of Escherichia coli transhydrogenase domain III with bound NADP(+) or NADPH has been carried out, in which the pH was varied between 5.4 and 12. In this analysis, individual amide protons served as reporter groups. The apparent pK(a) values of the amide protons, determined from the pH-dependent chemical shift changes, were attributed to actual pK(a) values for several titrating residues in the protein. The essential Asp392 is shown to be protonated at neutral pH in both the NADP(+) and NADPH forms of domain III, but with a marked difference in pK(a) not only attributable to the charge difference between the substrates. Titrating residues found in loop D/alpha5 point to a conformational difference of these structural elements that is redox-dependent, but not pH dependent. The observed apparent pK(a) values of these residues are discussed in relation to the crystal structure of Rhodospirillum rubrum domain III, the solution structure of E. coli domain III and the mechanism of intact proton-translocating transhydrogenase.
|
|
| 28. |
- Pellegrini, Mina, et al.
(författare)
-
MTERF2 is a nucleoid component in mammalian mitochondria.
- 2009
-
Ingår i: Biochimica et Biophysica Acta. - : Elsevier BV. - 0006-3002 .- 0005-2728. ; 1787:5, s. 296-302
-
Tidskriftsartikel (refereegranskat)abstract
- The mammalian MTERF family of proteins has four members, named MTERF1 to MTERF4, which were identified in homology searches using the mitochondrial transcription termination factor, mTERF (here denoted MTERF1) as query. MTERF1 and MTERF3 are known to participate in the control of mitochondrial DNA transcription, but the function of the other two proteins is not known. We here investigate the structure and function of MTERF2. Protein import experiments using isolated organelles confirm that MTERF2 is a mitochondrial protein. Edman degradation of MTERF2 isolated from stably transfected HeLa cells demonstrates that mature MTERF2 lacks a targeting peptide (amino acids 1-35) present in the precursor form of the protein. MTERF2 is a monomer in isolation and displays a non sequence-specific DNA-binding activity. In vivo quantification experiments demonstrate that MTERF2 is relatively abundant, with one monomer present per approximately 265 bp of mtDNA. In comparison, the mtDNA packaging factor TFAM is present at a ratio of one molecule per approximately 10-12 bp of mtDNA. Using formaldehyde cross-linking we demonstrate that MTERF2 is present in nucleoids, and therefore must be located in close proximity to mtDNA. Taken together, our work provides a basic biochemical characterization of MTERF2, paving the way for future functional studies.
|
|
| 29. |
- Pätsi, Jukka, et al.
(författare)
-
LHON/MELAS overlap mutation in ND1 subunit of mitochondrial complex I affects ubiquinone binding as revealed by modeling in Escherichia coli NDH-1.
- 2012
-
Ingår i: Biochimica et Biophysica Acta. - : Elsevier BV. - 0006-3002 .- 0005-2728. ; 1817:2, s. 312-318
-
Tidskriftsartikel (refereegranskat)abstract
- Defects in complex I due to mutations in mitochondrial DNA are associated with clinical features ranging from single organ manifestation like Leber hereditary optic neuropathy (LHON) to multiorgan disorders like mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) syndrome. Specific mutations cause overlap syndromes combining several phenotypes, but the mechanisms of their biochemical effects are largely unknown. The m.3376G > A transition leading to p.E24K substitution in ND1 with LHON/MELAS phenotype was modeled here in a homologous position (NuoH-E36K) in the Escherichia coli enzyme and it almost totally abolished complex I activity. The more conservative mutation NuoH-E36Q resulted in higher apparent Km for ubiquinone and diminished inhibitor sensitivity. A NuoH homolog of the m.3865A > G transition, which has been found concomitantly in the overlap syndrome patient with the m.3376G > A, had only a minor effect. Consequences of a primary LHON-mutation m.3460G > A affecting the same extramembrane loop as the m.3376G > A substitution were also studied in the E. coli model and were found to be mild. The results indicate that the overlap syndrome-associated m.3376G > A transition in MTND1 is the pathogenic mutation and m.3865A > G transition has minor, if any, effect on presentation of the disease. The kinetic effects of the NuoH-E36Q mutation suggest its proximity to the putative ubiquinone binding domain in 49 kD/PSST subunits. In all, m.3376G > A perturbs ubiquinone binding, a phenomenon found in LHON, and decreases the activity of fully assembled complex I as in MELAS.
|
|
| 30. |
- Ramos, ES, et al.
(författare)
-
Bioenergetic roles of mitochondrial fusion
- 2016
-
Ingår i: Biochimica et biophysica acta. - : Elsevier BV. - 0006-3002 .- 0005-2728. ; 1857:8, s. 1277-1283
-
Tidskriftsartikel (refereegranskat)
|
|
| 31. |
- Reimann, Joachim, et al.
(författare)
-
A pathway for protons in nitric oxide reductase from Paracoccus denitrificans
- 2007
-
Ingår i: Biochimica et Biophysica Acta. - : Elsevier BV. - 0006-3002 .- 1878-2434 .- 0005-2728. ; 1767:5, s. 362-373
-
Tidskriftsartikel (refereegranskat)abstract
- Nitric oxide reductase (NOR) from P. denitrificans is a membrane-bound protein complex that catalyses the reduction of NO to N2O (2NO + 2e(-) + 2H(+) -> N2O + H2O) as part of the denitriffication process. Even though NO reduction is a highly exergonic reaction, and NOR belongs to the superfamily of O-2-reducing, proton-pumping heme-copper oxidases (HCuOs), previous measurements have indicated that the reaction catalyzed by NOR is non-electrogenic, i.e. not contributing to the proton electrochemical gradient. Since electrons are provided by donors in the periplasm, this non-electrogenicity implies that the substrate protons are also taken up from the periplasm. Here, using direct measurements in liposome-reconstituted NOR during reduction of both NO and the alternative substrate O-2, we demonstrate that protons are indeed consumed from the 'outside'. First, multiple turnover reduction of O-2 resulted in an increase in pH on the outside of the NOR-vesicles. Second, comparison of electrical potential generation in NOR-liposomes during oxidation of the reduced enzyme by either NO or O-2 shows that the proton transfer signals are very similar for the two substrates proving the usefulness of O-2 as a model substrate for these studies. Last, optical measurements during single-turnover oxidation by O-2 show electron transfer coupled to proton uptake from outside the NOR-liposomes with a tau = 15 ms, similar to results obtained for net proton uptake in solubilised NOR [U. Flock, N.J. Watmough, P. Adelroth, Electron/proton coupling in bacterial nitric oxide reductase during reduction of oxygen, Biochemistry 44 (2005) 10711-10719]. NOR must thus contain a proton transfer pathway leading from the periplasmic surface into the active site. Using homology modeling with the structures of HCuOs as templates, we constructed a 3D model of the NorB catalytic subunit from P. denitrificans in order to search for such a pathway. A plausible pathway, consisting of conserved protonatable residues, is suggested.
|
|
| 32. |
- Rydström, Jan, 1943
(författare)
-
Mitochondrial NADPH, transhydrogenase and disease.
- 2006
-
Ingår i: Biochimica et biophysica acta. - : Elsevier BV. - 0006-3002 .- 0005-2728. ; 1757:5-6, s. 721-6
-
Tidskriftsartikel (refereegranskat)abstract
- Ever since its discovery in 1953 by N. O. Kaplan and coworkers, the physiological role of the proton-translocating transhydrogenase has generally been assumed to be that of generating mitochondrial NADPH. Mitochondrial NADPH can be used in a number of important reactions/processes, e.g., biosynthesis, maintenance of GSH, apoptosis, aging etc. This assumed role has found some support in bacteria but not in higher eukaryotes, a situation which changed dramatically with two recent but separate findings, both using transhydrogenase knockouts, in the nematode C. elegans and the mouse strain C57BL/6J. The latter, which is due to a spontaneous deletion mutation in the Nnt gene, was serendipitously found during investigations of the diabetic properties of these mice. The implications of these findings for the overall role of transhydrogenase in cell metabolism and disease are discussed.
|
|
| 33. |
- Shabalina, Irina G, et al.
(författare)
-
Cold tolerance of UCP1-ablated mice : A skeletal muscle mitochondria switch toward lipid oxidation with marked UCP3 up-regulation not associated with increased basal, fatty acid- or ROS-induced uncoupling or enhanced GDP effects.
- 2010
-
Ingår i: Biochimica et Biophysica Acta. - : Elsevier BV. - 0006-3002 .- 1878-2434 .- 0005-2728. ; 1797:6-7, s. 968-80
-
Tidskriftsartikel (refereegranskat)abstract
- Mice lacking the thermogenic mitochondrial membrane protein UCP1 (uncoupling protein 1) - and thus all heat production from brown adipose tissue - can still adapt to a cold environment (4 degrees C) if successively transferred to the cold. The mechanism behind this adaptation has not been clarified. To examine possible adaptive processes in the skeletal muscle, we isolated mitochondria from the hind limb muscles of cold-acclimated wild-type and UCP1(-/-) mice and examined their bioenergetic chracteristics. We observed a switch in metabolism, from carbohydrate towards lipid catabolism, and an increased total mitochondrial complement, with an increased total ATP production capacity. The UCP1(-/-) muscle mitochondria did not display a changed state-4 respiration rate (no uncoupling) and were less sensitive to the uncoupling effect of fatty acids than the wild-type mitochondria. The content of UCP3 was increased 3-4 fold, but despite this, endogenous superoxide could not invoke a higher proton leak, and the small inhibitory effect of GDP was unaltered, indicating that it was not mediated by UCP3. Double mutant mice (UCP1(-/-) plus superoxide dismutase 2-overexpression) were not more cold sensitive than UCP1(-/-), bringing into question an involvement of reactive oxygen species (ROS) in activation of any alternative thermogenic mechanism. We conclude that there is no evidence for an involvement of UCP3 in basal, fatty-acid- or superoxide-stimulated oxygen consumption or in GDP sensitivity. The adaptations observed did not imply any direct alternative process for nonshivering thermogenesis but the adaptations observed would be congruent with adaptation to chronically enhanced muscle activity caused by incessant shivering in these mice.
|
|
| 34. |
- Shabalina, Irina G, et al.
(författare)
-
Uncoupling protein-1 is not leaky.
- 2010
-
Ingår i: Biochimica et Biophysica Acta. - : Elsevier BV. - 0006-3002 .- 1878-2434 .- 0005-2728. ; 1797:6-7, s. 773-84
-
Tidskriftsartikel (refereegranskat)abstract
- The activity of uncoupling protein-1 (UCP1) is rate-limiting for nonshivering thermogenesis and diet-induced thermogenesis. Characteristically, this activity is inhibited by GDP experimentally and presumably mainly by cytosolic ATP within brown-fat cells. The issue as to whether UCP1 has a residual proton conductance even when fully saturated with GDP/ATP (as has recently been suggested) has not only scientific but also applied interest, since a residual proton conductance would make overexpressed UCP1 weight-reducing even without physiological/pharmacological activation. To examine this question, we have here established optimal conditions for studying the bioenergetics of wild-type and UCP1(-/-) brown-fat mitochondria, analysing UCP1-mediated differences in parallel preparations of brown-fat mitochondria from both genotypes. Comparing different substrates, we find that pyruvate (or palmitoyl-l-carnitine) shows the largest relative coupling by GDP. Comparing albumin concentrations, we find the range 0.1-0.6% optimal; higher concentrations are inhibitory. Comparing basic medium composition, we find 125mM sucrose optimal; an ionic medium (50-100mM KCl) functions for wild-type but is detrimental for UCP1(-/-) mitochondria. Using optimal conditions, we find no evidence for a residual proton conductance (not a higher post-GDP respiration, a lower membrane potential or an altered proton leak at highest common potential) with either pyruvate or glycerol-3-phosphate as substrates, nor by a 3-4-fold alteration of the amount of UCP1. We could demonstrate that certain experimental conditions, due to respiratoty inhibition, could lead to the suggestion that UCP1 possesses a residual proton conductance but find that under optimal conditions our experiments concur with implications from physiological observations that in the presence of inhibitory nucleotides, UCP1 is not leaky.
|
|
| 35. |
- Shevela, Dmitriy, et al.
(författare)
-
Probing the turnover efficiency of photosystem II membrane fragments with different electron acceptors
- 2012
-
Ingår i: Biochimica et Biophysica Acta. - : Elsevier. - 0006-3002 .- 1878-2434 .- 0005-2728 .- 1879-2650. ; 1817:8, s. 1208-1212
-
Tidskriftsartikel (refereegranskat)abstract
- In this study we employ isotope ratio membrane-inlet mass spectrometry to probe the turnover efficiency of photosystem II (PSII) membrane fragments isolated from spinach at flash frequencies between 1Hz and 50Hz in the presence of the commonly used exogenous electron acceptors potassium ferricyanide(III) (FeCy), 2,5-dichloro-p-benzoquinone (DCBQ), and 2-phenyl-p-benzoquinone (PPBQ). The data obtained clearly indicate that among the tested acceptors PPBQ is the best at high flash frequencies. If present at high enough concentration, the PSII turnover efficiency is unaffected by flash frequency of up to 30Hz, and at 40Hz and 50Hz only a slight decrease by about 5-7% is observed. In contrast, drastic reductions of the O(2) yields by about 40% and 65% were found at 50Hz for DCBQ and FeCy, respectively. Comparison with literature data reveals that PPBQ accepts electrons from Q(A)(-) in PSII membrane fragments with similar efficiency as plastoquinone in intact cells. Our data also confirm that at high flashing rates O(2) evolution is limited by the reactions on the electron-acceptor side of PSII. The relevance of these data to the evolutionary development of the water-splitting complex in PSII and with regard to the potential of artificial water-splitting catalysts is discussed. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial Photosynthesis.
|
|
| 36. |
- Shi, Lan-Xin, et al.
(författare)
-
Photosystem II, a growing complex : Updates on newly discovered components and low molecular mass proteins
- 2012
-
Ingår i: Biochimica et Biophysica Acta. - : Elsevier. - 0006-3002 .- 1878-2434 .- 0005-2728. ; 1817:1, s. 13-25
-
Tidskriftsartikel (refereegranskat)abstract
- Photosystem II is a unique complex capable of absorbing light and splitting water. The complex has been thoroughly studied and to date there are more than 40 proteins identified, which bind to the complex either stably or transiently. Another special feature of this complex is the unusually high content of low molecular mass proteins that represent more than half of the proteins. In this review we summarize the recent findings on the low molecular mass proteins (<15 kDa) and present an overview of the newly identified components as well. We have also performed co-expression analysis of the genes encoding PSII proteins to see if the low molecular mass proteins form a specific sub-group within the Photosystem II complex. Interestingly we found that the chloroplast-localized genes encoding PSII proteins display a different response to environmental and stress conditions compared to the nuclear localized genes. This article is part of a Special Issue entitled: Photosystem II.
|
|
| 37. |
- Su, Ji-Hu, et al.
(författare)
-
The electronic structures of the S(2) states of the oxygen evolving complexes of photosystem II in plants and cyanobacteria in the presence and absence of methanol
- 2011
-
Ingår i: Biochimica et Biophysica Acta. - Amsterdam : Elsevier. - 0006-3002 .- 1878-2434 .- 0005-2728 .- 1879-2650. ; 1807:7, s. 829-840
-
Tidskriftsartikel (refereegranskat)abstract
- The electronic properties of the Mn(4)O(x)Ca cluster in the S(2) state of the oxygen evolving complex (OEC) were studied using X- and Q-band EPR and Q-band (55)Mn-ENDOR using photosystem II preparations isolated from the thermophilic cyanobacterium T. elongatus and higher plants (spinach). The data presented here show that there is very little difference between the two species. Specifically it is shown that: (i) only small changes are seen in the fitted isotropic hyperfine values, suggesting that there is no significant difference in the overall spin distribution (electronic coupling scheme) between the two species; (ii) the inferred fine-structure tensor of the only Mn(III) ion in the cluster is of the same magnitude and geometry for both species types, suggesting that the Mn(III) ion has the same coordination sphere in both sample preparations; and (iii) the data from both species are consistent with only one structural model available in the literature, namely the Siegbahn structure [Siegbahn, P. E. M. Accounts Chem. Res.2009, 42, 1871-1880, Pantazis, D. A. et al., Phys. Chem. Chem. Phys.2009, 11, 6788-6798]. These measurements were made in the presence of methanol because it confers favorable magnetic relaxation properties to the cluster that facilitate pulse-EPR techniques. In the absence of methanol the separation of the ground state and the first excited state of the spin system is smaller. For cyanobacteria this effect is minor but in plant PS II it leads to a break-down of the S(T)=½ spin model of the S(2) state. This suggests that the methanol-OEC interaction is species dependent. It is proposed that the effect of small organic solvents on the electronic structure of the cluster is to change the coupling between the outer Mn (Mn(A)) and the other three Mn ions that form the trimeric part of the cluster (Mn(B), Mn(C), Mn(D)), by perturbing the linking bis-μ-oxo bridge. The flexibility of this bridging unit is discussed with regard to the mechanism of O-O bond formation.
|
|
| 38. |
- Trifunovic, A
(författare)
-
Mitochondrial DNA and ageing
- 2006
-
Ingår i: Biochimica et biophysica acta. - : Elsevier BV. - 0006-3002 .- 0005-2728. ; 1757:5-6, s. 611-617
-
Tidskriftsartikel (refereegranskat)
|
|
| 39. |
- Wanrooij, Sjoerd, et al.
(författare)
-
The human mitochondrial replication fork in health and disease.
- 2010
-
Ingår i: Biochimica et biophysica acta. - : Elsevier BV. - 0006-3002 .- 0005-2728.
-
Forskningsöversikt (refereegranskat)abstract
- Mitochondria are organelles whose main function is to generate power by oxidative phosphorylation. Some of the essential genes required for this energy production are encoded by the mitochondrial genome, a small circular double stranded DNA molecule. Human mtDNA is replicated by a specialized machinery distinct from the nuclear replisome. Defects in the mitochondrial replication machinery can lead to loss of genetic information by deletion and/or depletion of the mtDNA, which subsequently may cause disturbed oxidative phosphorylation and neuromuscular symptoms in patients. We discuss here the different components of the mitochondrial replication machinery and their role in disease. We also review the mode of mammalian mtDNA replication.
|
|
| 40. |
- Deák, Zsuzsanna, et al.
(författare)
-
Methanol modification of the electron paramagnetic resonance signals from the S0 and S2 states of the water-oxidizing complex of Photosystem II
- 1999
-
Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - 0005-2728. ; 1412:3, s. 240-249
-
Tidskriftsartikel (refereegranskat)abstract
- The Mn-derived electron paramagnetic resonance (EPR) multiline signal from the S0 state of the water-oxidizing complex is observable only in the presence methanol. In the present study, we have characterized the effect of methanol on the EPR signals from the S0 and S2 states as well as on the EPR Signal IIslow originating from the TyrosineDox radical. The amplitudes of the S0 and S2 multiline signals increase with the methanol concentration in a similar way, whereas the S2 g=4.1 excited state signal amplitude shows a concomitant decrease. The methanol concentration at which half of the spectral change has occurred is ~0.2% and the effect is saturating around 5%. Methanol has an effect on the microwave power saturation of the S2 multiline signal, as well. The microwave power at half saturation (P1/2) is 85 mW in the presence of methanol, whereas the signal relaxes much slower (P1/2~27 mW) without. The relaxation of Signal IIslow in the presence of methanol has also been investigated. The P1/2 value of Signal IIslow oscillates with the S cycle in a similar way as without methanol, but the P1/2 values are consistently lower in the methanol-containing samples. From the results, we conclude that methanol modifies the magnetic properties of the S0 and S2 states in a similar way. The possible site and nature of methanol binding is discussed.
|
|
| 41. |
- Gadjieva, Rena, et al.
(författare)
-
Fractionation of the thylakoid membranes from tobacco. A tentative isolation of ‘end membrane’ and purified ‘stroma lamellae’ membranes
- 1999
-
Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - 0005-2728. ; 1411:1, s. 92-100
-
Tidskriftsartikel (refereegranskat)abstract
- Thylakoids isolated from tobacco were fragmented by sonication and the vesicles so obtained were separated by partitioning in aqueous polymer two-phase systems. By this procedure, grana vesicles were separated from stroma exposed membrane vesicles. The latter vesicles could be further fractionated by countercurrent distribution, with dextran-polyethylene glycol phase systems, and divided into two main populations, tentatively named 'stroma lamellae' and 'end membrane'. Both these vesicle preparations have high chlorophyll a/b ratio, high photosystem (PS) I and low PS II content, suggesting their origin from stroma exposed regions of the thylakoid. The two vesicle populations have been compared with respect to biochemical composition and photosynthetic activity. The 'end membrane' has a higher chlorophyll a/b ratio (5.7 vs. 4.7), higher P700 content (4.7 vs. 3.3 mmol/mol of chlorophyll). The 'end membrane' has the lowest PS II content, the ratio PS I/PS II being more than 10, as shown by EPR measurements. The PS II in both fractions is of the β-type. The decay of fluorescence is different for the two populations, the 'stroma lamellae' showing a very slow decay even in the presence of K3Fe(CN)6 as an acceptor. The two vesicle populations have very different surface properties: the end membranes prefer the upper phase much more than the stroma lamellae, a fact which was utilized for their separation. Arguments are presented which support the suggestion that the two vesicle populations originate from the grana end membranes and the stroma lamellae, respectively.
|
|
| 42. |
- Geijer, Paulina, et al.
(författare)
-
Comparative studies of the S0 and S2 multiline electron paramagnetic resonance signals from the manganese cluster in Photosystem II
- 2001
-
Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - 0005-2728. ; 1503:1-2, s. 83-95
-
Tidskriftsartikel (refereegranskat)abstract
- Electron paramagnetic resonance (EPR) spectroscopy is one of the major techniques used to analyse the structure and function of the water oxidising complex (WOC) in Photosystem II. The discovery of an EPR signal from the S0 state has opened the way for new experiments, aiming to characterise the S0 state and elucidate the differences between the different S states. We present a review of the biochemical and biophysical characterisation of the S0 state multiline signal that has evolved since its discovery, and compare these results to previous and recent data from the S2 multiline signal. We also present some new data from the S2 state reached on the second turnover of the enzyme.
|
|
| 43. |
- Hammarström, Leif, et al.
(författare)
-
Artificial photosynthesis: towards functional mimics of photosystem II?
- 1998
-
Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - 0005-2728. ; 1365:1-2, s. 193-199
-
Tidskriftsartikel (refereegranskat)abstract
- This paper describes the initial development of a project aiming at the construction of functional mimics of the oxygen-evolving complex of photosystem II, coupled to photoinduced charge separation. Biomimetic electron donors, manganese complexes and tyrosine, have been linked to a Ru(II)-polypyridine photosensitiser. Oxidation of the donors by intramolecular electron transfer from the photo-oxidised Ru(III) complex was demonstrated using optical flash photolysis and EPR experiments. A step-wise electron transfer Mn->tyrosine->Ru(III) was demonstrated.
|
|
| 44. |
- Hederstedt, Lars
(författare)
-
Succinate:quinone oxidoreductase in the bacteria Paracoccus denitrificans and Bacillus subtilis.
- 2002
-
Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - 0005-2728. ; 1553:1-2, s. 74-83
-
Tidskriftsartikel (refereegranskat)abstract
- An overview of the present knowledge about succinate:quinone oxidoreductase in Paracoccus denitrificans and Bacillus subtilis is presented. P. denitrificans contains a monoheme succinate:ubiquinone oxidoreductase that is similar to that of mammalian mitochondria with respect to composition and sensitivity to carboxin. Results obtained with carboxin-resistant P. denitrificans mutants provide information about quinone-binding sites on the enzyme and the molecular basis for the resistance. B. subtilis contains a diheme succinate:menaquinone oxidoreductase whose activity is dependent on the electrochemical gradient across the cytoplasmic membrane. Data from studies of mutant variants of the B. subtilis enzyme combined with available crystal structures of a similar enzyme, Wolinella succinogenes fumarate reductase, substantiate a proposed explanation for the mechanism of coupling between quinone reductase activity and transmembrane potential.
|
|
| 45. |
- Hägerhäll, Cecilia, et al.
(författare)
-
The trinuclear iron-sulfur cluster S-3 in Bacillus subtilis succinate:menaquinone reductase; effects of a mutation in the putative cluster ligation motif on enzyme activity and EPR properties
- 1995
-
Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - 0005-2728. ; 1229:3, s. 356-362
-
Tidskriftsartikel (refereegranskat)abstract
- Succinate:quinone reductases (SQRs) and quinol:fumarate reductases (QFRs) each contain a bi-, a tri- and a tetra-nuclear iron-sulfur cluster. The C-terminal half of the iron-sulfur protein subunit of these enzymes shows two fully conserved motifs of cysteine residues, stereotypical for ligands of [3Fe-4S] and [4Fe-4S] clusters. To analyze the functional role of the trinuclear cluster S3 in Bacillus subtilis SQR, a fourth cysteine residue was introduced into the putative ligation motif to that cluster. A corresponding mutation in Escherichia coli QFR results in a tri- to tetranuclear conversion (Manodori et al. (1992) Biochemistry 31, 2703–2731). We have found that presence of the extra cysteine in B. subtilis SQR does not result in cluster conversion. It does, however, affect the EPR properties of the cluster S3, whereas those of the other two clusters remain normal. The results strongly support the view that residues in the most C-terminal cysteine motif in the iron-sulfur protein subunit of SQRs and QFRs ligate the trinuclear cluster. Compared to wild-type SQR, S3 in the B. subtilis mutant enzyme is not sensitive to methanol and the midpoint redox potential is close to normal. The quinone reductase activity of the mutant enzyme is only 35% of normal. Thus, the architecture around cluster S3 plays a role in electron transfer to quinone or in the binding of quinone to the enzyme.
|
|
| 46. |
- Jansson, Stefan, et al.
(författare)
-
Antenna protein composition of PS I and PS II in thylakoid sub-domains
- 1997
-
Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - 0005-2728. ; 1320:3, s. 297-309
-
Tidskriftsartikel (refereegranskat)abstract
- Spinach thylakoids were separated into grana core, grana margin, and two different stromal lamella fractions in the absence of detergents. The levels of all light-harvesting chlorophyll a/b-binding (LHC) proteins were determined in all fractions, and were normalised to the amount of Photosystem I (PS I) and Photosystem II (PS II) centres. PS Iβ in the stroma lamellae was found to have a full complement of Lhca polypeptides and, probably, one attached LHC II trimer. PS Iα binds additional LHC II trimers, but PS I centres located in the inner parts of the grana stack lack Lhca1 and are depleted in Lhca4. PS IIβ, found in grana margins and stroma lamellae, seems to associate one monomer each of Lhcb4, Lhcb5 and Lhcb6 (CP29, CP26 and CP24, respectively) and one LHC II trimer consisting of two Lhcb1 and one Lhcb3 subunit. PS IIα has additional LHC II trimers (consisting of Lhcb1 and Lhcb2) attached. We also find evidence for the existence of both PS I and PS II centres in the extreme stroma (probably centres being synthesised or repaired), that lack all LHC proteins.
|
|
| 47. |
- Magnusson, Ann, et al.
(författare)
-
The role of cytochrome b559 and tyrosineD in protection against photoinhibition during in vivo photoactivation of Photosystem II
- 1999
-
Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - 0005-2728. ; 1411:1, s. 180-191
-
Tidskriftsartikel (refereegranskat)abstract
- In vivo photoactivation of Photosystem II was studied in the FUD39 mutant strain of the green alga Chlamydomonas reinhardtii which lacks the 23 kDa protein subunit involved in water oxidation. Dark grown cells, devoid of oxygen evolution, were illuminated at 0.8 μE m-2&#;s-1 light intensity which promotes optimal activation of oxygen evolution, or at 17 μE m-2&#;s-1, where photoactivation compete with deleterious photodamage. The involvement of the two redox active cofactors tyrosineD and cytochrome b559 during the photoactivation process, was investigated by EPR spectroscopy. TyrosineD on the D2 reaction center protein functions as auxiliary electron donor to the primary donor P680+ during the first minutes of photoactivation at 0.8 μE m-2&#;s-1 (compare with Rova et al., Biochemistry, 37 (1998) 11039-11045.). Here we show that also cytochrome b559 was rapidly oxidized during the first 10 min of photoactivation with a similar rate to tyrosineD. This implies that both cytochrome b559 and tyrosineD may function as auxiliary electron donors to P680+ and/or the oxidized tyrosine&#;Z on the D1 protein, to avoid photoinhibition before successful photoactivation was accomplished. As the catalytic water-oxidation successively became activated, TyrosineD remained oxidized while cytochrome b559 became rereduced to the equilibrium level that was observed prior to photoactivation. At 17 μE m-2&#;s-1 light intensity, where photoinhibition competes significantly with photoactivation, tyrosineD was very rapidly completely oxidized, after which the amount of oxidized tyrosineD decreased due to photoinhibition. In contrast, cytochrome b559 became reduced during the first 2 min of photoactivation at 17 μE m-2&#;s-1. After this, it was reoxidized, returning to the equilibrium level within 10 min. Thus, during in vivo photoactivation in high-light cytochrome b559 serves two functions. Initially, it probably oxidizes the reduced primary acceptor pheophytin, thereby relieving the acceptor side of reductive pressure, and later on it serves as auxiliary electron donor, preventing donor-side photoinhibition.
|
|
| 48. |
- Mathiesen, Cecilie, et al.
(författare)
-
Transmembrane topology of the NuoL, M and N subunits of NADH:quinone oxidoreductase and their homologues among membrane-bound hydrogenases and bona fide antiporters
- 2002
-
Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - 0005-2728. ; 1556:2-3, s. 121-132
-
Tidskriftsartikel (refereegranskat)abstract
- Nicotinamide adenine dinucleotide-reduced form (NADH):quinone oxidoreductase (respiratory Complex I), F420H2 oxidoreductase and complex, membrane-bound NiFe-hydrogenase contain protein subunits homologous to a certain type of bona fide antiporters. In Complex I, these polypeptides (NuoL/ND5, NuoM/ND4, NuoN/ND2) are most likely core components of the proton pumping mechanism, and it is thus important to learn more about their structure and function. In this work, we have determined the transmembrane topology of one such polypeptide, and built a 2D structural model of the protein valid for all the homologous polypeptides. The experimentally determined transmembrane topology was different from that predicted by majority vote hydrophobicity analyses of members of the superfamily. A detailed phylogenetic analysis of a large set of primary sequences shed light on the functional relatedness of these polypeptides.
|
|
| 49. |
- Pettersson, Gösta
(författare)
-
Control properties of the Calvin photosynthesis cycle at physiological carbon dioxide concentrations
- 1997
-
Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - 0005-2728. ; 1322:2-3, s. 173-182
-
Tidskriftsartikel (refereegranskat)abstract
- A previously described kinetic model for the Calvin cycle and ancillary pathway of starch production in the chloroplast of C3 plants has been extended so that it becomes applicable under physiological conditions where there is a competition between carbon dioxide and oxygen for ribulose-1,5-bisphosphate carboxylase (rubisco). The modified model is shown to account for the observed dependencies of the rate of carbon dioxide assimilation in leaves on the concentrations of carbon dioxide, oxygen, and rubisco. The predictions of the model are examined with particular regard to the control characteristics of the photosynthetic process of carbohydrate formation under physiological conditions.
|
|
| 50. |
- Rasmusson, Allan G., et al.
(författare)
-
Physiological, biochemical and molecular aspects of mitochondrial complex I in plants
- 1998
-
Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - 0005-2728. ; 1364:2, s. 101-111
-
Tidskriftsartikel (refereegranskat)abstract
- Respiratory complex I of plant mitochondria has to date been investigated with respect to physiological function, biochemical properties and molecular structure. In the respiratory chain complex I is the major entry gate for low potential electrons from matrix NADH, reducing ubiquinone and utilizing the released energy to pump protons across the inner membrane. Plant complex I is active against a background of several other NAD(P)H dehydrogenases, which do not contribute in proton pumping, but permit and establish several different routes of shuttling electrons from NAD(P)H to ubiquinone. Identification of the corresponding molecular structures, that is the proteins and genes of the different NADH dehydrogenases, will allow more detailed studies of this interactive regulatory network in plant mitochondria. Present knowledge of the structure of complex I and the respective mitochondrial and nuclear genes encoding various subunits of this complex in plants is summarized here. Copyright (C) 1998 Elsevier Science B.V.
|
|
