| 1. |
- Beck, M., et al.
(författare)
-
Evaluation of the energetic position of the lowest excited singlet state of beta-carotene by NEXAFS and photoemission spectroscopy
- 2001
-
Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - 0005-2728 .- 1879-2650. ; 1506:3, s. 260-267
-
Tidskriftsartikel (refereegranskat)abstract
- In carotenoids the lowest energetic optical transition belonging to the pi -electron system is forbidden by symmetry, therefore the energetic position of the S-1 (2(1)A(g)) level can hardly be assessed by optical spectroscopy. We introduce a novel experimental approach: For molecules with ir-electron systems the transition C1s --> 2p(pi*) from inner-atomic to the lowest unoccupied molecular orbital (LUMO) appears in X-ray absorption near edge spectra (NEXAFS) as an intense, sharp peak a few eV below the carbon K-edge. Whereas the peak position reflects the energy of the First excited singlet state in relation to the ionization potential of the molecule, intensity and width of the transition depend on hybridization and bonding partners of the selected atom. Complementary information can be obtained from ultraviolet photoelectron spectroscopy (UPS): At the low binding energy site of the spectrum a peak related to the highest occupied molecular orbital (HOMO) appears. We have measured NEXAFS and UPS of beta -carotene. Based on these measurements and quantum chemical calculations the HOMO and LUMO energies can be derived.
|
|
| 2. |
- Borodich, A, et al.
(författare)
-
Segregation of the photosystems in thylakoids depends on their size
- 2003
-
Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - 0005-2728 .- 1879-2650. ; 1606:1-3, s. 73-82
-
Tidskriftsartikel (refereegranskat)abstract
- Lateral segregation of two types of photosystems in thylakoid membranes of green plants is one of the key factors that provide the stability and fine-tuning of the light quanta supply by pigment proteins and non-cyclic electron transport. Due to this specific feature of the membrane structural organization, the photosynthetic units function in the green plants with optimal performance. In this report a mesoscopic theory is outlined to address the physical aspects of segregation phenomenon. Results of theoretical studies and computer simulations suggest that charge mismatch and the size difference between two photosystems in grana are most responsible for their lateral segregation, which is driven by the screened electrostatic and lipid-induced interactions. Comparative simulations of photosystems of different sizes show the crucial dependence of their ordering on a geometrical parameter. It seems that the size effect alone may prevent photosystems from segregated arrangement in cyanobacterial thylakoids. (C) 2003 Elsevier B.V. All rights reserved.
|
|
| 3. |
- Glaser, Elzbieta, et al.
(författare)
-
Plant mitochondrial protein import : precursor processing is catalysed by the integrated mitochondrial processing peptidase (MPP)/bc1 complex and degradation by the ATP-dependent proteinase
- 1996
-
Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - : Elsevier BV. - 0005-2728 .- 1879-2650. ; 1275:1-2, s. 33-37
-
Tidskriftsartikel (refereegranskat)abstract
- Several hundreds of mitochondrial proteins are nuclear encoded and are synthesised on cytosolic polyribosomes as precursor proteins. Most of these precursors contain an N-terminal extension called presequence which functions as targeting signal and which is cleaved off after import. Despite the fact that there are no sequence similarities and no consensus for the cleavage site in mitochondrial presequences, cleavage of almost all presequences is catalysed by a single, highly specific metalloendopeptidase, called general mitochondrial processing peptidase (MPP). MPP in plants is integrated into the bc1, complex of the respiratory chain and both subunits, α-MPP and β-MPP, are identical to the core proteins of the complex. Despite the fact that the bc1 complex in plants is bifunctional, catalysing bothelectron transport and protein processing, these two functions are distinct. MPP belongs to the Pitrilysin family of peptidases, characterised by a zinc binding motif, HXXEH74–76E, involved in catalysis. Both the membrane-bound integrated MPP/bc1 complex of plants and the soluble mammalian MPP recognise similar higher-order structural elements upstream from the cleavage site that are important for processing. The secondary structure with flexibility and stabilising elements, hydrofobicity, charge and length seem to influence the interaction with MPP. The newly imported non-assembled precursor inside mitochondria is degraded by a proteinase that is distinct from MPP or any other previously characterised proteinases, a novel ATP-dependent, membrane-associated serine-type proteinase.
|
|
| 4. |
- Igamberdiev, A U, et al.
(författare)
-
Regulation of NAD- and NADP-dependent isocitrate dehydrogenases by reduction levels of pyridine nucleotides in mitochondria and cytosol of pea leaves
- 2003
-
Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - 0005-2728 .- 1879-2650. ; 1606:1-3, s. 117-125
-
Tidskriftsartikel (refereegranskat)abstract
- Regulation of NAD- and NADP-dependent isocitrate dehydrogenases (NAD-ICDH, EC 1.1.1.41, and NADP-ICDH, EC 1.1.1.42) by the level of reduced and oxidized pyridine nucleotides has been investigated in pea (Pisum sativum L.) leaves. The affinities of mitochondrial and cytosolic ICDH enzymes to substrates and inhibitors were determined on partially purified preparations in forward and reverse directions. From the kinetic data, it follows that NADP(+)- and NAD+-dependent isocitrate dehydrogenases in mitochondria represent a system strongly responding to the intramitochondrial NADPH and NADH levels. The NADPH, NADP(+), NADH and NAD(+) concentrations were determined by subcellular fractionation of pea leaf protoplasts using membrane filtration in mitochondria and cytosol in darkness and in the light under saturating and limiting CO2 Conditions. The cytosolic NADPH/NADP ratio was about I and almost constant both in darkness and in the light. In mitochondria, the NADPH/NADP ratio was low in darkness (0.2) and increased in the light, reaching 3 in limiting CO2 conditions compared to I in saturating CO2. At high reduction levels of NADP and NAD observed at limiting CO2 in the light, i.e. when photorespiratory glycine is the main mitochondrial substrate, isocitrate oxidation in mitochondria will be suppressed and citrate will be transported to the cytosol ('citrate valve'), where the cytosolic NADP-ICDH supplies 2-oxoglutarate for the photorespiratory ammonia refixation. (C) 2003 Elsevier B.V. All rights reserved.
|
|
| 5. |
- Mason, M. G., et al.
(författare)
-
The heme domain of cellobiose oxidoreductase : a one-electron reducing system
- 2003
-
Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - : Elsevier BV. - 0005-2728 .- 1879-2650. ; 1604:1, s. 47-54
-
Tidskriftsartikel (refereegranskat)abstract
- Phanerochaete chrysosporium cellobiose oxidoreductase (CBOR) comprises two redox domains, one containing flavin adenine dinucleotide (FAD) and the other protoheme. It reduces both two-electron acceptors, including molecular oxygen, and one-electron acceptors, including transition metal complexes and cytochrome c. If the latter reacts with the flavin, the reduced heme b acts merely as a redox buffer, but if with the b heme, enzyme action involves a true electron transfer chain. Intact CBOR fully reduced with cellobiose, CBOR partially reduced by ascorbate, and isolated ascorbate-reduced heme domain, all transfer electrons at similar rates to cytochrome c. Reduction of cationic one-electron acceptors via the heme group supports an electron transfer chain model. Analogous reactions with natural one-electron acceptors can promote Fenton chemistry, which may explain evolutionary retention of the heme domain and the enzyme's unique character among secreted sugar dehydrogenases.
|
|
| 6. |
- Messinger, Johannes, 1963-
(författare)
-
Towards understanding the chemistry of photosynthetic oxygen evolution : dynamic structural changes, redox states and substrate water binding of the Mn cluster in photosystem II
- 2000
-
Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - Tech Univ Berlin, Max Volmer Inst, D-10623 Berlin, Germany. : ELSEVIER. - 0005-2728 .- 1879-2650. ; 1459:2-3, s. 481-488
-
Tidskriftsartikel (refereegranskat)abstract
- This mini-review summarizes my postdoctoral research in the labs of T. Wydrzynski/C.B. Osmond, J.H.A. Nugent/M.C.W. Evans and V.K. Yachandra/K. Sauer/M.P. Klein. The results are reported in the context of selected data from the literature. Special emphasis is given to the mode of substrate water binding, Mn oxidation states and the structures of the Mn cluster in the four (meta)stable redox states of the oxygen evolving complex. The paper concludes with a working model for the mechanism of photosynthetic water oxidation that combines CL-oxo bridge oxidation in the S-3 State (V.K. Yachandra, K. Sauer, M.P. Klein, Chem. Rev. 96 (1996) 2927-2950) with O-O bond formation between two terminal Mn-hydroxo ligands during the S-3 --> (S-4) --> S-0 transition. (C) 2000 Elsevier Science B.V. All rights reserved.
|
|
| 7. |
- Paul, Jan, et al.
(författare)
-
Ab initio calculations of electron distributions in heme-CO models
- 1983
-
Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - : Elsevier BV. - 0005-2728 .- 1879-2650. ; 722:1, s. 209-213
-
Tidskriftsartikel (refereegranskat)abstract
- We have, by the use of ab initio calculations, found a back-bonding state of π symmetry close to the Fermi level for CO bound to FeN5C14. We thus find it likely that small shifts of the redox potential ¦EF - Ev¦ will cause relatively large changes of the CO vibrational frequency. The separation of Fe 3d orbitals in our heme model is found to agree with what is predicted by ligand field theory for Oh symmetry. This paper presents nonrelativistic Hartree-Fock-Slater calculations of the 5σ bonding and 2π back-bonding between CO and Fe. The effects of up to 19 additional atoms are discussed for models of heme (COFe to COFeN5C14). The filled back-bonding state is found to be strongly influenced by second nearest neighbor atoms. By use of symmetry orbitals we have resolved the Fe 3d orbitals into the T2g and Eg representations of the Oh point group and find the former states to be occupied whereas the latter are unoccupied. The difference in occupancy is reduced when the CO ligand is removed which also causes an increased density of states at the Fermi level, i.e., the highest occupied and lowest unoccupied orbitals. Possible correlations between our data and experimental results are discussed for heme proteins as well as for metal surfaces.
|
|
| 8. |
- Persson, Bengt L., et al.
(författare)
-
ATP-driven transhydrogenase provides an example of delocalized chemiosmotic coupling in reconstituted vesicles and in submitochondrial particles
- 1987
-
Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - : Elsevier BV. - 0005-2728 .- 1879-2650. ; 894:2, s. 239-251
-
Tidskriftsartikel (refereegranskat)abstract
- The mechanism of coupling between mitochondrial ATPase (EC 3.6.1.3) and nicotinamide nucleotide transhydrogenase (EC 1.6.1.1) was studied in reconstituted liposomes containing both purified enzymes and compared with their behavior in submitochondrial particles. In order to investigate the mode of coupling between the transhydrogenase and the ATPase by the double-inhibitor and inhibitor-uncoupler methods, suitable inhibitors of transhydrogenase and ATPase were selected. Phenylarsine oxide and A3′-O-(3-(N-(4-azido-2-nitrophenyl)amino)propionyl)-NAD+ were used as transhydrogenase inhibitors, whereas of the various ATPase inhibitors tested aurovertin was found to be the most convenient. The inhibition of the ATP-driven transhydrogenase activity was proportional to the inhibition of both the ATPase and the transhydrogenase. Inhibitor-uncoupler titrations showed an increased sensitivity of the coupled reaction towards carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) — an uncoupler that preferentially uncouples localized interactions, according to Herweijer et al. (Biochim. Biophys. Acta 849 (1986) 276–287) — when the primary pump was partially inhibited. However, when the secondary pump was partially inhibited the sensitivity towards FCCP remained unchanged. Similar results were obtained with submitochondrial particles. These results are in contrast to those obtained previously with the ATP-driven reverse electron flow. In addition, the amount of uncoupler required for uncoupling of the ATP-driven transhydrogenase was found to be similar to that required for the stimulation of the ATPase activity, both in reconstituted vesicles and in submitochondrial particles. Uncoupling of reversed electron flow to NAD+ required much less uncoupler. On the basis of these results, it is proposed that, in agreement with the chemiosmotic model, the interaction between ATPase and transhydrogenase in reconstituted vesicles as well as in submitochondrial particles occurs through the [...]. In contrast, the energy transfer between ATPase and NADH-ubiquinone oxidoreductase appears to occur via a more direct interaction, according to the above-mentioned results by Herweijer et al.
|
|
| 9. |
- Petronilli, V, et al.
(författare)
-
Flow-force relationships during energy transfer between mitochondrial proton pumps
- 1991
-
Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - 0005-2728 .- 1879-2650. ; 1058:2, s. 297-303
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of inhibitors of proton pumps, of uncouplers and of permeant ions on the relationship between input force, , and output flows of the ATPase, redox and transhydrogenase H+-pumps in submitochondrial particles was investigated. It is concluded that: (1) The decrease of output flow of the transhydrogenase proton pump, defined as the rate of reduction of NADP+ by NADH, is linearily correlated with the decrease of input force, , in an extended range of , independently of whether the H+-generating pump is the ATPase or a redox pump, or whether is depressed by inhibitors of the H+-generating pump such as oligomycin or malonate, or by uncouplers. (2) The output flows of the ATPase and of the site I redox H+-pumps exhibit a steep dependence on . The flow-force relationships differ depending on whether the depression of is induced by inhibitors of the H+-generating pump, by uncouplers or by lipophilic anions. (3) With the ATPase as H+-consuming pump, at equivalent values, the output flow is more markedly inhibited by malonate than by uncouplers; the latter, however, are more inhibitory than lipophilic anions such as ClO4−. With redox site I as proton-consuming pump, at equivalent values, the output flow is more markedly inhibited by oligomycin than by uncouplers; again, uncouplers are more inhibitory than ClO4−. (4) The results provide further support for a delocalized interaction of transhydrogenase with other H+-pumps.
|
|
| 10. |
- Abou-Hamdan, Abbas, et al.
(författare)
-
Functional design of bacterial superoxide : quinone oxidoreductase
- 2022
-
Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - : Elsevier BV. - 0005-2728 .- 1879-2650. ; 1863:7
-
Tidskriftsartikel (refereegranskat)abstract
- The superoxide anion - molecular oxygen reduced by a single electron - is produced in large amounts by enzymatic and adventitious reactions. It can perform a range of cellular functions, including bacterial warfare and iron uptake, signalling and host immune response in eukaryotes. However, it also serves as precursor for more deleterious species such as the hydroxyl anion or peroxynitrite and defense mechanisms to neutralize superoxide are important for cellular health. In addition to the soluble proteins superoxide dismutase and superoxide reductase, recently the membrane embedded diheme cytochrome b561 (CybB) from E. coli has been proposed to act as a superoxide:quinone oxidoreductase. Here, we confirm superoxide and cellular ubiquinones or menaquinones as natural substrates and show that quinone binding to the enzyme accelerates the reaction with superoxide. The reactivity of the substrates is in accordance with the here determined midpoint potentials of the two b hemes (+48 and -23 mV / NHE). Our data suggest that the enzyme can work near the diffusion limit in the forward direction and can also catalyse the reverse reaction efficiently under physiological conditions. The data is discussed in the context of described cytochrome b561 proteins and potential physiological roles of CybB.
|
|
