| 1. |
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| 2. |
- Mizuno, T., et al.
(författare)
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A Monte Carlo method for calculating the energy response of plastic scintillators to polarized photons below 100 keV
- 2009
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 600:3, s. 609-617
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Tidskriftsartikel (refereegranskat)abstract
- The energy response of plastic scintillators (Eljen Technology EJ-204) to polarized soft gamma-ray photons below 100 keV has been studied, primarily for the balloon-borne polarimeter, PoGOLite. The response calculation includes quenching effects due to low-energy recoil electrons and the position dependence of the light collection efficiency in a 20 cm long scintillator rod. The broadening of the pulse-height spectrum, presumably caused by light transportation processes inside the scintillator, as well as the generation and multiplication of photoelectrons in the photomultiplier tube, were studied experimentally and have also been taken into account. A Monte Carlo simulation based on the Geant4 toolkit was used to model photon interactions in the scintillators. When using the polarized Compton/Rayleigh scattering processes previously corrected by the authors, scintillator spectra and angular distributions of scattered polarized photons could clearly be reproduced, in agreement with the results obtained at a synchrotron beam test conducted at the KEK Photon Factory. Our simulation successfully reproduces the modulation factor, defined as the ratio of the amplitude to the mean of the distribution of the azimuthal scattering angles, within similar to 5% (relative). Although primarily developed for the PoGOLite mission, the method presented here is also relevant for other missions aiming to measure polarization from astronomical objects using plastic scintillator scatterers.
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| 3. |
- Tamás, Markus J., 1970, et al.
(författare)
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A Short Regulatory Domain Restricts Glycerol Transport through Yeast Fps1p
- 2003
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Ingår i: J. Biol. Chem. ; 278, s. 6337-6345
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Tidskriftsartikel (refereegranskat)abstract
- The controlled export of solutes is crucial for cellular adaptation to hypotonic conditions. In the yeast Saccharomyces cerevisiae glycerol export is mediated by Fps1p, a member of the major intrinsic protein (MIP) family of channel proteins. Here we describe a short regulatory domain that restricts glycerol transport through Fps1p. This domain is required for retention of cellular glycerol under hypertonic stress and hence acquisition of osmotolerance. It is located in the N-terminal cytoplasmic extension close to the first transmembrane domain. Several residues within that domain and its precise position are critical for channel control while the proximal residues 13-215 of the N-terminal extension are not required. The sequence of the regulatory domain and its position are perfectly conserved in orthologs from other yeast species. The regulatory domain has an amphiphilic character, and structural predictions indicate that it could fold back into the membrane bilayer. Remarkably, this domain has structural similarity to the channel forming loops B and E of Fps1p and other glycerol facilitators. Intragenic second-site suppressor mutations of the sensitivity to high osmolarity conferred by truncation of the regulatory domain caused diminished glycerol transport, confirming that elevated channel activity is the cause of the osmosensitive phenotype.
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| 4. |
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| 5. |
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| 6. |
- Bill, Roslyn M., et al.
(författare)
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Analysis of the pore of the unusual major intrinsic protein channel, yeast Fps1p.
- 2001
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Ingår i: The Journal of biological chemistry. - 0021-9258 .- 1083-351X. ; 276:39, s. 36543-9
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Tidskriftsartikel (refereegranskat)abstract
- Fps1p is a glycerol efflux channel from Saccharomyces cerevisiae. In this atypical major intrinsic protein neither of the signature NPA motifs of the family, which are part of the pore, is preserved. To understand the functional consequences of this feature, we analyzed the pseudo-NPA motifs of Fps1p by site-directed mutagenesis and assayed the resultant mutant proteins in vivo. In addition, we took advantage of the fact that the closest bacterial homolog of Fps1p, Escherichia coli GlpF, can be functionally expressed in yeast, thus enabling the analysis in yeast cells of mutations that make this typical major intrinsic protein more similar to Fps1p. We observed that mutations made in Fps1p to "restore" the signature NPA motifs did not substantially affect channel function. In contrast, when GlpF was mutated to resemble Fps1p, all mutants had reduced activity compared with wild type. We rationalized these data by constructing models of one GlpF mutant and of the transmembrane core of Fps1p. Our model predicts that the pore of Fps1p is more flexible than that of GlpF. We discuss the fact that this may accommodate the divergent NPA motifs of Fps1p and that the different pore structures of Fps1p and GlpF may reflect the physiological roles of the two glycerol facilitators.
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| 7. |
- Chauvin, Maxime, et al.
(författare)
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The design and flight performance of the PoGOLite Pathfinder balloon-borne hard X-ray polarimeter
- 2016
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Ingår i: Experimental astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 41:1, s. 17-41
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Tidskriftsartikel (refereegranskat)abstract
- In the 50 years since the advent of X-ray astronomy there have been many scientific advances due to the development of new experimental techniques for detecting and characterising X-rays. Observations of X-ray polarisation have, however, not undergone a similar development. This is a shortcoming since a plethora of open questions related to the nature of X-ray sources could be resolved through measurements of the linear polarisation of emitted X-rays. The PoGOLite Pathfinder is a balloon-borne hard X-ray polarimeter operating in the 25-240 keV energy band from a stabilised observation platform. Polarisation is determined using coincident energy deposits in a segmented array of plastic scintillators surrounded by a BGO anticoincidence system and a polyethylene neutron shield. The PoGOLite Pathfinder was launched from the SSC Esrange Space Centre in July 2013. A near-circumpolar flight was achieved with a duration of approximately two weeks. The flight performance of the Pathfinder design is discussed for the three Crab observations conducted. The signal-to-background ratio for the observations is shown to be 0.25 ±0.03 and the Minimum Detectable Polarisation (99 % C.L.) is (28.4 ±2.2) %. A strategy for the continuation of the PoGOLite programme is outlined based on experience gained during the 2013 maiden flight.
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| 8. |
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| 9. |
- Persson, Bengt L., et al.
(författare)
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ATP-driven transhydrogenase provides an example of delocalized chemiosmotic coupling in reconstituted vesicles and in submitochondrial particles
- 1987
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Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - : Elsevier BV. - 0005-2728 .- 1879-2650. ; 894:2, s. 239-251
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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.
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| 10. |
- Persson, Bengt L., et al.
(författare)
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NBD-Cl modification of essential residues in mitochondrial nicotinamide nucleotide transhydrogenase from beef heart
- 1988
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Ingår i: Biochimica et Biophysica Acta - Protein Structure and Molecular Enzymology. - : Elsevier BV. - 0167-4838 .- 1879-2588. ; 953, s. 241-248
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Tidskriftsartikel (refereegranskat)abstract
- Modification of mitochondrial nicotinamide nucleotide transhydrogenase (NADPH:NAD+ oxidoreductase, EC 1.6.1.1) with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl), followed by measurement of the absorption or fluorescence of the transhydrogenase-NBD adducts, resulted in a biphasic labelling of approx. 4–6 sulfhydryls, presumably cysteine residues. Of these 1–2 (27%) were fast-reacting and 3–4 (73%) slow-reacting sulfhydryls. In the presence of substrates, e.g., NADPH, the labelling was monophasic and all sulfhydryls were fast-reacting, suggesting that the modified sulfhydryls are predominantly localized peripheral to the NAD(P)(H)-binding sites. The rates of modification allowed the calculation of the rate constants for each phase of the labelling. Both in the absence and in the presence of a substrate, e.g., NADPH, the extent of labelling essentially parallelled the inhibition of transhydrogenase activity. Attempts to reactivate transhydrogenase by reduction of labelled sulfhydryls were not successful. Photo-induced transfer of the NBD adduct in partially inhibited transhydrogenase, from the sulfhydryls to reactive NH2 groups of amino-acid residue(s), identified as lysine residue(s), was parallelled by an inhibition of the residual transhydrogenase activity. It is suggested that a lysine localized close to the fast-reacting NBD-Cl-reactive sulfhydryl groups is essential for activity.
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| 11. |
- Sindi, S., et al.
(författare)
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Multimodal Preventive Trial for Alzheimer’s Disease : MIND-ADmini Pilot Trial Study Design and Progress
- 2022
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Ingår i: The Journal of Prevention of Alzheimer's Disease. - : Serdi-Editions. - 2274-5807 .- 2426-0266. ; 9:1, s. 30-39
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Tidskriftsartikel (refereegranskat)abstract
- Background: Interventions simultaneously targeting multiple risk factors and mechanisms are most likely to be effective in preventing cognitive impairment. This was indicated in the Finnish Geriatric Intervention Study to Prevent Cognitive Impairment and Disability (FINGER) testing a multidomain lifestyle intervention among at-risk individuals. The importance of medical food at the early symptomatic disease stage, prodromal Alzheimer’s disease (AD), was emphasized in the LipiDiDiet trial. The feasibility and effects of multimodal interventions in prodromal AD are unclear. Objectives: To evaluate the feasibility of an adapted FINGER-based multimodal lifestyle intervention, with or without medical food, among individuals with prodromal AD. Methods: MIND-ADmini is a multinational proof-of-concept 6-month randomized controlled trial (RCT), with four trial sites (Sweden, Finland, Germany, France). The trial targeted individuals with prodromal AD defined using the International Working Group-1 criteria, and with vascular or lifestyle-related risk factors. The parallel-group RCT includes three arms: 1) multimodal lifestyle intervention (nutritional guidance, exercise, cognitive training, vascular/metabolic risk management and social stimulation); 2) multimodal lifestyle intervention+medical food (Fortasyn Connect); and 3) regular health advice/ care (control group). Primary outcomes are feasibility and adherence. Secondary outcomes are adherence to the individual intervention domains and healthy lifestyle changes. Results: Screening began on 28 September 2017 and was completed on 21 May 2019. Altogether 93 participants were randomized and enrolled. The intervention proceeded as planned. Conclusions: For the first time, this pilot trial tests the feasibility and adherence to a multimodal lifestyle intervention, alone or combined with medical food, among individuals with prodromal AD. It can serve as a model for combination therapy trials (non-pharma, nutrition-based and/or pharmacological interventions).
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| 12. |
- Takahashi, H., et al.
(författare)
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A thermal-neutron detector with a phoswich system of LiCaAlF6 and BGO crystal scintillators onboard PoGOLite
- 2010
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Ingår i: 2010 IEEE Nuclear Science Symposium, Medical Imaging Conference, NSS/MIC 2010 and 17th International Workshop on Room-Temperature Semiconductor X-ray and Gamma-ray Detectors, RTSD 2010. ; , s. 32-37
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Konferensbidrag (refereegranskat)abstract
- To measure the flux of atmospheric neutrons and study the neutron contribution to the background of the main detector of the PoGOLite (Polarized Gamma-ray Observer) balloon-borne experiment, a thermal-neutron detector with a phoswich system of LiCaAlF6 (Eu) and BGO crystal scintillators is developed. The performance to separate thermal-neutron events from those of gamma-rays and charged particles is validated with 252Cf on ground. The detector is attached to the PoGOLite instrument and is launched in 2011 from the Esrange facility in the North of Sweden. Although the emission wavelength of the LiCaAlF6 (Ce) is 300 nm and overlaps with the absorption wavelength of the BGO, the phoswich capability of the LiCaAlF6 (Ce) with the BGO is also confirmed with installing a waveform shifter.
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| 13. |
- Takahashi, H., et al.
(författare)
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The Polarized Gamma-Ray Observer, PoGOLite
- 2010
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Ingår i: Transactions of the Japanese Society for Artificial Intelligence, Aerospace Technology Japan. - 1346-0714 .- 1346-0714. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- The Polarized Gamma-ray Observer, PoGOLite, is a balloon experiment with the capability of detecting 10% polarization from a 200 mCrab celestial object in the energy-range 25–80 keV. During a beam test at KEK-PF in 2008, 19 detector units and one anti-coincidence detector were assembled, and a 50 keV X-ray beam with a polarization degree of ∼90% was irradiated at the center unit. Signals from all 20 units were fed into flight-version electronics consisting of six circuit boards (four waveform digitizer boards, one digital I/O board and one router board) and one microprocessor (SpaceCube), which communicate using a SpaceWire interface. One digitizer board, which can associate up to 8 detectors, outputs a trigger signal. The digital I/O board handles the trigger and returns a data acquisition request if there is no veto signal (upper or pulse-shape discriminators) from any detector unit. This data acquisition system worked well, and the modulation factor was successfully measured to be ∼34%. These results confirmed the capabilities of the data-acquisition system for a “pathfinder” flight planned in 2010.
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| 14. |
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| 15. |
- Carlenor, E, et al.
(författare)
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On the presence of a nicotinamide nucleotide transhydrogenase in mitochondria from potato tuber
- 1988
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Ingår i: Plant Physiology. - 0032-0889 .- 1532-2548. ; 88, s. 303-308
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Tidskriftsartikel (refereegranskat)abstract
- Mitochondria isolated from potato (Solanum tuberosum L.) tuber wereinvestigated for the presence of a nicotinamide nucleotide transhydrogenaseactivity. Submitochondrial particles derived from these mitochondriaby sonication catalyzed a reduction of NAD' or 3-acetylpyridine-NAD'by NADPH, which showed a maximum of about 50 to 150 nanomoles/minute. milligram protein at pH 5 to 6. The Km values for 3-acetylpyridine-NAD' and NADPH were about 24 and 55 micromolar, respectively.Intact mitochondria showed a negligible activity in the absence of detergents.However, in the presence of detergents the specific activity approachedabout 30% of that seen with submitochondrial particles. Thepotato mitochondria transhydrogenase activity was sensitive to trypsinand phenylarsine oxide, both agents that are known to inhibit the mammaliantranshydrogenase. Antibodies raised against rat liver transhydrogenasecrossreacted with two peptides in potato tuber mitochondrialmembranes with a molecular mass of 100 to 115 kilodaltons. Theobserved transhydrogenase activities may be due to an unspecific activityof dehydrogenases and/or to a genuine transhydrogenase. The activitycontributions by NADH dehydrogenases and transhydrogenase to thetotal transhydrogenase activity were investigated by determining theirrelative sensitivities to trypsin. It is concluded that, at high or neutralpH, the observed transhydrogenase activity in potato tuber submitochondrialparticles is due to the presence of a genuine and specific highmolecular weight transhydrogenase. At low pH an unspecific reaction ofan NADH dehydrogenase with NADPH contributes to the total transhydrogenaseactivity.
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| 16. |
- Chauvin, Maxime, et al.
(författare)
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Observation of polarized hard X-ray emission from the Crab by the PoGOLite Pathfinder
- 2016
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 456:1, s. L84-L88
-
Tidskriftsartikel (refereegranskat)abstract
- We have measured the linear polarization of hard X-ray emission from the Crab in a previously unexplored energy interval, 20-120 keV. The introduction of two new observational parameters, the polarization fraction and angle stands to disentangle geometrical and physical effects, thereby providing information on the pulsar wind geometry and magnetic field environment. Measurements are conducted using the PoGOLite Pathfinder - a balloon-borne polarimeter. Polarization is determined by measuring the azimuthal Compton scattering angle of incident X-rays in an array of plastic scintillators housed in an anticoincidence well. The polarimetric response has been characterized prior to flight using both polarized and unpolarized calibration sources. We address possible systematic effects through observations of a background field. The measured polarization fraction for the integrated Crab light curve is 18.4(-10.6)(+9.8) per cent, corresponding to an upper limit (99 per cent credibility) of 42.4 per cent, for a polarization angle of (149.2 +/- 16.0)degrees.
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| 17. |
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| 18. |
- Clyne, N, et al.
(författare)
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The intracellular distribution of cobalt in exposed and unexposed rat myocardium
- 1990
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Ingår i: Scandinavian Journal of Clinical and Laboratory Investigation. - 0036-5513 .- 1502-7686. ; 50:6, s. 605-609
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Tidskriftsartikel (refereegranskat)abstract
- The intracellular distribution of cobalt was analysed in the myocardium of exposed and unexposed rats. The exposed rats were given a dietary cobalt supplementation of 40 mg CoS04-7 H20/kg body weight for 8 weeks. The mitochondrial fraction showed the greatest relative increase in cobalt: 0.09 ng/mg protein in the unexposed rats to 8.43 ng/mg protein in the exposed rats. In the exposed rats the submitochondrial particles had the highest levels of cobalt: 19.43 ng/mg protein, followed by the sarcoplasmatic reticulum: 12.3 ng/mg protein. The microsomal 44 000g supernatant also showed an increase, although the levels remained low (0.51 ng/mg protein in the exposed animals). Apparently the calcium-storing organelles had the highest levels of cobalt. This could affect calcium flux in myocardial cells and, secondarily, tension development in cardiac muscle.
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| 19. |
- Eytan, G D, et al.
(författare)
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Energy-linked nicotinamide-nucleotide transhydrogenase. Characterization of reconstituted ATP-driven transhydrogenase from beef heart mitochondria.
- 1987
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 262, s. 5008-5014
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between pure transhydrogenase and ATPase (Complex V) from beef heart mitochondria was investigated with transhydrogenase-ATPase vesicles in which the two proteins were co-reconstituted by dialysis or dilution procedures. In addition to phosphatidylcholine and phosphatidylethanolamine, reconstitution required phosphatidylserine and lysophosphatidylcholine. Transhydrogenase-ATPase vesicles catalyzed a 20-30-fold stimulation of the reduction of NADP+ or thio-NADP+ by NADH and a 70-fold shift of the apparent equilibrium expressed as the nicotinamide nucleotide ratio [NADPH][NAD+]/[NADP+][NADH]. In both of these respects, the transhydrogenase-ATPase vesicles were severalfold more efficient than beef heart submitochondrial particles. By measuring the ATP-driven transhydrogenase and the oligomycin-sensitive ATPase activities simultaneously and under the same conditions at low ATP concentrations, i.e. below 15 microM, the ATP-driven transhydrogenase/oligomycin-sensitive ATPase activity ratio was found to be about 3. This value is consistent with the stoichiometries of three protons translocated per ATP hydrolyzed and one proton translocated per NADPH formed and with a mechanism where the two enzymes interact through a delocalized proton-motive force.
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| 20. |
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| 21. |
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| 22. |
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| 23. |
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| 24. |
- Hedfalk, Kristina, 1969, et al.
(författare)
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A Regulatory Domain in the C-terminal Extension of the Yeast Glycerol Channel Fps1p
- 2004
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Ingår i: Journal of biological chemistry. ; 279:15, s. 14954-14960
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Tidskriftsartikel (refereegranskat)abstract
- The Saccharomyces cerevisiae gene FPS1 encodes an aquaglyceroporin of the major intrinsic protein (MIP) family. The main function of Fps1p seems to be the efflux of glycerol in the adaptation of the yeast cell to lower external osmolarity. Fps1p is an atypical member of the family, because the protein is much larger (669 amino acids) than most MIPs due to long hydrophilic extensions in both termini. We have shown previously that a short domain in the N-terminal extension of the protein is required for restricting glycerol transport through the channel (Tamás, M. J., Karlgren, S., Bill, R. M., Hedfalk, K., Allegri, L., Ferreira, M., Thevelein, J. M., Rydström, J., Mullins, J. G. L., and Hohmann, S. (2003) J. Biol. Chem. 278, 63376345). Deletion of the N-terminal domain results in an unregulated channel, loss of glycerol, and osmosensitivity. In this work we have investigated the role of the Fps1p C terminus (139 amino acids). A set of eight truncations has been constructed and tested in vivo in a yeast fps1 strain. We have performed growth tests, membrane localization following cell fractionation, and glycerol accumulation measurements as well as an investigation of the osmotic stress response. Our results show that the C-terminal extension is also involved in restricting transport through Fps1p. We have identified a sequence of 12 amino acids, residues 535546, close to the sixth transmembrane domain. This element seems to be important for controlling Fps1p function. Similar to the N-terminal domain, the C-terminal domain is amphiphilic and has a potential to dip into the membrane
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| 25. |
- Höjeberg, B, et al.
(författare)
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Affinity Chromatography and Binding Studies on Immobilized Adenosine 5'-Monophosphate and Adenosine 2'.5'-Bisphosphate of Nicotinamide Nucleotide Transhydrogenase from Pseudomonas aeruginosa
- 1976
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Ingår i: European Journal of Biochemistry. - : Wiley. - 0014-2956 .- 1432-1033. ; 66:3, s. 467-475
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Tidskriftsartikel (refereegranskat)abstract
- Nicotinamide nucleotide transhydrogenase from Pseudomonas aeruginosa was purified to apparent homogeneity with an improved method employing affinity chromatography on N6-(6-aminoyl)-adenosine-2′,5′-bisphosphate-Sepharose 4B. Polyacrylamide gel electrophoresis of the purified transhydrogenase carried out in the presence of sodium dodecyl sulphate, indicated a minimal molecular weight of 55000 ± 2000. The kinetic and regulatory properties of the purified transhydrogenase resembled those of the crude enzyme, i.e., NADPH, adenosine 2′-monophosphate and Ca2+were activators whereas NADP+was inhibitory. Nicotinamide nucleotide-specific release of binding of the transhydrogenase to N6-(6-aminohexyl)-adenosine-2′,5′-bisphosphate-Sepharose and N6-(6-aminohexyl)-adenosine-5′-monophospliate-Sepharose suggests the presence of at least two separate binding sites for nicotinamide nucleotides, one that is specific for NADP(H) and one that binds both NAD(H) and NADP(H). Binding of transhydrogenase to N6-(6-aminohexyl)-adenosine-2′,5′-bisphosphate-Sepharose and activation of the enzyme by adenosine-2′,5′-bisphosphate showed a marked pH dependence. In contrast, inhibition of the Ca2+-activated enzyme by adenosine 2′,5′-bisphosphate was virtually constant at various pH values. This discrepancy was interpreted to indicate the existence of separate nucleotide-binding effector and active sites.
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| 26. |
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| 27. |
- Karlsson, J, et al.
(författare)
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Roles of Individual Amino Acids in Helix 14 of the Membrane Domain of Proton-Translocating Transhydrogenase from Escherichia coli As Deduced from Cysteine Mutagenesis
- 2003
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Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 42, s. 6575-6581
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Tidskriftsartikel (refereegranskat)abstract
- Proton-translocating nicotinamide nucleotide transhydrogenase is a membrane-bound protein composed of three domains: the hydrophilic NAD(H)-binding domain, the hydrophilic NADP(H)-binding domain, and the hydrophobic membrane domain. The latter harbors the proton channel. In Escherichia coli transhydrogenase, the membrane domain is composed of 13 transmembrane helices, of which especially helices 13 and 14 contain conserved residues. To characterize the roles of the individual residues Leu240 to Ser260 in helix 14, these were mutated as single mutants to cysteines in the cysteine-free background, and in the case of Gly245, Gly249, and Gly252, also to leucines. In addition to the residues forming the helix, residues Asn238 and Asp239 were also mutated. Except for I242C, all mutants were normally expressed, purified, and characterized with respect to, e.g., catalytic activities and proton pumping. The results show that mutation of the conserved glycines Gly245, Gly249, and Gly252, located on the same face of the helix, led to a general inhibition of all activities, especially in the case of Gly252, suggesting a role of these glycines in helix-helix interactions. In contrast, mutation of the conserved serines Ser250, Ser251, and Ser256 led to enhanced activities of all reactions, including the cyclic reaction which was mediated by bound NADP(H). Mutation of the remaining residues resulted in intermediate inhibitory effects. The results strongly support an important regulatory role of the membrane domain on the NADP(H)-binding site.
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| 28. |
- Kiss, Mózsi, et al.
(författare)
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The PoGOLite balloon-borne soft gamma-ray polarimeter
- 2008
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Ingår i: COOL DISCS, HOT FLOWS. - : AIP. ; , s. 225-232
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Konferensbidrag (refereegranskat)abstract
- Linearly polarized radiation in the hard X-ray/soft gamma-ray band is expected from a large variety of astronomical sources. We discuss the importance of polarimetric studies for several classes of sources - pulsars, accreting black holes. magnetic neutron stars and jets from active galaxies - and then describe PoGOLite, a balloon-borne instrument which is currently under construction and will be able to measure the polarization of electromagnetic radiation from such extra-solar objects in the energy range 25-80 keV.
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| 29. |
- Kullander, Klas, et al.
(författare)
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Role of EphA4 and EphrinB3 in local neuronal circuits that control walking
- 2003
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 299:5614, s. 1889-1892
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Tidskriftsartikel (refereegranskat)abstract
- Local circuits in the spinal cord that generate locomotion are termed central pattern generators (CPGs). These provide coordinated bilateral control over the normal limb alternation that underlies walking. The molecules that organize the mammalian CPG are unknown. Isolated spinal cords from mice lacking either the EphA4 receptor or its ligand ephrinB3 have lost left-right limb alternation and instead exhibit synchrony. We identified EphA4-positive neurons as an excitatory component of the locomotor CPG. Our study shows that dramatic locomotor changes can occur as a consequence of local genetic rewiring and identifies genes required for the development of normal locomotor behavior.
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| 30. |
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| 31. |
- Pearce, Mark, et al.
(författare)
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Balloon-borne hard X-ray polarimetry with PoGOLite
- 2012
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Ingår i: 2012 IEEE Nuclear Science Symposium and Medical Imaging Conference Record (NSS/MIC). - : IEEE. - 9781467320306 ; , s. 1885-1892
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Konferensbidrag (refereegranskat)abstract
- PoGOLite is a hard X-ray polarimeter operating in the 25-100 keV energy band. The instrument design is optimised for the observation of compact astrophysical sources. Observations are conducted from a stabilised stratospheric balloon platform at an altitude of approximately 40 km. The primary targets for first balloon flights of a reduced effective area instrument are the Crab and Cygnus-X1. The polarisation of incoming photons is determined using coincident Compton scattering and photo-absorption events reconstructed in an array of plastic scintillator detector cells surrounded by a bismuth germanate oxide (BGO) side anticoincidence shield and a polyethylene neutron shield. A custom attitude control system keeps the polarimeter field-of-view aligned to targets of interest, compensating for sidereal motion and perturbations such as torsional forces in the balloon rigging. An overview of the PoGOLite project is presented and the outcome of the ill-fated maiden balloon flight is discussed.
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| 32. |
- Pedersen, Anders, 1976, et al.
(författare)
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Properties of the apo-form of the NADP(H)-binding domain III of proton-pumping Escherichia coli transhydrogenase: implications for the reaction mechanism of the intact enzyme
- 2003
-
Ingår i: Biochim.Biophys. Acta (Bioenergetics). ; 1604, s. 55-59
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Tidskriftsartikel (refereegranskat)abstract
- Proton-translocating nicotinamide nucleotide transhydrogenases contain an NAD(H)-binding domain (dI), an NADP(H)-binding domain (dIII) and a membrane domain (dII) with the proton channel. Separately expressed and isolated dIII contains tightly bound NADP(H), predominantly in the oxidized form, possibly representing a so-called “occluded” intermediary state of the reaction cycle of the intact enzyme. Despite a Kd in the micromolar to nanomolar range, this NADP(H) exchanges significantly with the bulk medium. Dissociated NADP+ is thus accessible to added enzymes, such as NADP-isocitrate dehydrogenase, and can be reduced to NADPH. In the present investigation, dissociated NADP(H) was digested with alkaline phosphatase, removing the 2′-phosphate and generating NAD(H). Surprisingly, in the presence of dI, the resulting NADP(H)-free dIII catalyzed a rapid reduction of 3-acetylpyridine-NAD+ by NADH, indicating that 3-acetylpyridine-NAD+ and/or NADH interacts unspecifically with the NADP(H)-binding site. The corresponding reaction in the intact enzyme is not associated with proton pumping. It is concluded that there is a 2′-phosphate-binding region in dIII that controls tight binding of NADP(H) to dIII, which is not a required for fast hydride transfer. It is likely that this region is the Lys424–Arg425–Ser426 sequence and loops D and E. Further, in the intact enzyme, it is proposed that the same region/loops may be involved in the regulation of NADP(H) binding by an electrochemical proton gradent.
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| 33. |
- Persson, Bengt L., et al.
(författare)
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A circular dichroism study of mitochondrial transhydrogenase from beef heart
- 1991
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Ingår i: Biophysical Chemistry. - 0301-4622 .- 1873-4200. ; 39:3, s. 267-272
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes a circular dichroism (CD) spectroscopy study of purified proton-pumping nicotinamide nucleotide transhydrogenase from beef heart. The CD spectrum obtained was used to estimate the content of secondary structures of the purified enzyme and suggests the presence of 40–45% α-helical structure and long, possibly membrane-spanning α-helices. The spectrum was essentially unaffected by the absence or presence of transhydrogenase substrates, suggesting that the catalytic and proton-translocating activities of the enzyme occur without major rearrangements at the level of secondary structures.
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| 34. |
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| 35. |
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| 36. |
- Persson, Bengt L., et al.
(författare)
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Energy-linked nicotinamide nucleotide transhydrogenase : Properties of proton-translocating mitochondrial transhydrogenase from beef heart purified by fast protein liquid chromatography
- 1984
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 259, s. 8626-8632
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Tidskriftsartikel (refereegranskat)abstract
- Mitochondrial nicotinamide nucleotide transhydrogenasefrom beef heart was purified by a novel procedureinvolving fast protein liquid chromatography andcharacterized with respect to molecular and catalyticproperties. The method is reproducible, gives highlypure transhydrogenase as judged by silver staining,and can be modified to produce large amounts of puretranshydrogenase protein suitable for e.g. sequencingand other protein chemical studies.Transhydrogenase purified by fast protein liquidchromatography is reconstitutively active and pumpsprotons as indicated by an extensive quenching of 9-aminoacridine fluorescence. Under conditions whichgenerate a proton gradient in the absence of a membranepotential the activity of reconstituted transhydrogenaseis close to zero indicating a complete andproper incorporation in the membrane and a preferentialregulation of the enzyme by a proton gradientrather than a membrane potential.Treatment of reconstituted transhydrogenase withN,N-dicyclohexylcarbodiimide results in an inhibitionof proton pump activity without an effect on uncoupledcatalytic activity, suggestingt hat proton translocationand catalytic activities are not obligatory linked orthat this agent separates proton pumping from thecatalytic activity.
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| 37. |
- Persson, Bengt L., et al.
(författare)
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Energy-linked nicotinamide nucleotide transhydrogenase. Hydrodynamic properties and active form of purified and membrane-bound mitochondrial transhydrogenase from beef heart
- 1987
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Ingår i: Archives of Biochemistry and Biophysics. - : Elsevier BV. - 0003-9861 .- 1096-0384. ; 259:2, s. 341-349
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Tidskriftsartikel (refereegranskat)abstract
- The mitochondrial nicotinamide nucleotide transhydrogenase from beef heart was investigated with respect to minimal assembly of the purified enzyme and of the enzyme in the mitochondrial inner membrane. Studies of the hydrodynamic properties of the purified enzyme in the presence of 0.3% Triton X-100 allowed determination of the Stokes radius, sedimentation constant, partial specific volume, frictional ratio, and molecular weight. Under these conditions transhydrogenase existed as an inactive monomer, suggesting that monomerization may be accompanied by inactivation. Radiation inactivation was used to determine the functional molecular size of purified detergent-dispersed transhydrogenase and transhydrogenase in beef heart submitochondrial particles. Under these conditions the catalytic activity of both the purified and the membrane-bound enzyme was found to be catalyzed by a dimeric form of the enzyme. These results suggest for the first time that the minimal functional assembly of detergent-dispersed as well as membrane-bound transhydrogenase is a dimer, which is not functionally associated with, for example, complex I or ATPase. In addition, the results are consistent with the possibility that the two subunits of transhydrogenase are catalytically active in an alternating fashion according to a previously proposed half-of-the-sites reactivity model.
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| 38. |
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| 39. |
- Petronilli, V, et al.
(författare)
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Flow-force relationships during energy transfer between mitochondrial proton pumps
- 1991
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Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - 0005-2728 .- 1879-2650. ; 1058:2, s. 297-303
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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.
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| 40. |
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| 41. |
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| 42. |
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| 43. |
- TIGERSTRÖM, ANNA KATARINA, 1976, et al.
(författare)
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Functional split and crosslinking of the membrane domain of the beta subunit of proton-translocating transhydrogenase from Escherichia coli
- 2003
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Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 42, s. 10998-11003
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Tidskriftsartikel (refereegranskat)abstract
- Proton pumping nicotinamide nucleotide transhydrogenase from Escherichia coli contains an alpha subunit with the NAD(H)-binding domain I and a beta subunit with the NADP(H)-binding domain III. The membrane domain (domain II) harbors the proton channel and is made up of the hydrophobic parts of the alpha and beta subunits. The interface in domain II between the alpha and the beta subunits has previously been investigated by cross-linking loops connecting the four transmembrane helices in the alpha subunit and loops connecting the nine transmembrane helices in the beta subunit. However, to investigate the organization of the nine transmembrane helices in the beta subunit, a split was introduced by creating a stop codon in the loop connecting transmembrane helices 9 and 10 by a single mutagenesis step, utilizing an existing downstream start codon. The resulting enzyme was composed of the wild-type alpha subunit and the two new peptides beta1 and beta2. As compared to other split membrane proteins, the new transhydrogenase was remarkably active and catalyzed activities for the reduction of 3-acetylpyridine-NAD(+) by NADPH, the cyclic reduction of 3-acetylpyridine-NAD(+) by NADH (mediated by bound NADP(H)), and proton pumping, amounting to about 50-107% of the corresponding wild-type activities. These high activities suggest that the alpha subunit was normally folded, followed by a concerted folding of beta1 + beta2. Cross-linking of a betaS105C-betaS237C double cysteine mutant in the functional split cysteine-free background, followed by SDS-PAGE analysis, showed that helices 9, 13, and 14 were in close proximity. This is the first time that cross-linking between helices in the same beta subunit has been demonstrated.
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