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1.
Simultaneous measurements of 9-aminoacridine (9-AA) fluorescence quenching, O2-uptake and chlorophyll fluorescence of intact spinach chloroplasts were carried out to assess the relationship between the transthylakoidal pH and linear electron flux passing through Photosystem II. Three different types of O2-dependent electron flow were investigated: (1) Catalysed by methyl viologen; (2) in the absence of a catalyst and presence of an active ascorbate peroxidase (Mehler-peroxidase reaction); (3) in the absence of a catalyst and with the ascorbate peroxidase being inhibited by KCN (Mehler reaction). The aim of this study was to assess the relative contribution of pH-formation which is not associated with electron flow through Photosystem II and, which should reflect Photosystem I cyclic flow under the different conditions. The relationship between the extent of 9-AA fluorescence quenching and O2-uptake rate was found to be almost linear when methyl viologen was present. In the absence of methyl viologen (Mehler reaction) an increase of 9-AA fluorescence quenching to a value of 20% at low light intensities was associated with considerably less O2-uptake than in the presence of methyl viologen, indicating the involvement of cyclic flow. These findings are in agreement with a preceding study of Kobayashi and Heber (1994). However, when no KCN was added, such that the complete Mehler-peroxidase reaction sequence was operative, the relationship between 9-AA fluorescence quenching and the flux through PS II, as measured via the chlorophyll fluorescence parameter F/Fm × PAR, was identical to that observed in the presence of methyl viologen. Under the assumption that methyl viologen prevents cyclic flow, it is concluded that there is no significant contribution of cyclic electron flow to pH-generation in intact spinach chloroplasts. 相似文献
2.
Boris Ivanov 《Free radical research》2013,47(3):217-227
In spinach thylakoids prepared from intact chloroplasts by shocking in the presence of ascorbate to preserve the operation of ascorbate peroxidase, the rate of oxygen uptake with methyl viologen as acceptor decreased in response to the addition of H2O2. Such a decrease was not observed in the presence of KCN or when the thylakoids lost ascorbate peroxidase activity. Illumination of intact chloroplasts in the presence of H2O2 and methyl viologen showed an initial rate of oxygen exchange, which is intermediate between the initial rate of oxygen evolution in the presence of H2O2 alone and steady-state oxygen uptake in the presence of methyl viologen. The data showed that monodehydroascorbate radical generated in ascorbate peroxidase reaction could compete with methyl viologen for electrons supplied by the electron transport chain in both thylakoids and intact chloroplasts. During the illumination of intact chloroplasts the rate of oxygen uptake increased. The presence of nigericin swiftly led to steady-state oxygen uptake, and to a clear-cut 1:1 relationship between the electron transport rate estimated from fluorescence assay and the electron transport rate determined from oxygen uptake, taking the stoichiometry 1O2:4e. The increase in oxygen uptake was attributed to the cessation of monodehydroascorbate radical generation brought about by consumption of intrachloroplast ascorbate in the peroxidase reactions, and the effects of nigericin were explained by acceleration of such consumption. The competition between methyl viologen and monodehydroascorbate radical in the intact chloroplasts was estimated under various conditions. 相似文献
3.
Potential roles for cyclic and pseudocyclic electron flow in C4 plants are to provide ATP for the C4 cycle and, under excess light, to down-regulate PS II activity through membrane energization. Intact mesophyll chloroplasts of maize were used to evaluate forms of electron transport including the Mehler peroxidase reaction (linear electron flow to O2, formation of H2O2 which is reduced by ascorbate, and linear flow linked to reduction of oxidized ascorbate). Addition of H2O2 to isolated chloroplasts in the light in the presence of an uncoupler induced Photosystem (PS) II activity, as determined from increases in photochemical quenching of chlorophyll fluorescence (qp) and the quantum yield of PS II. H2O2 also induced dissipation of energy by thylakoid membrane energization and non-photochemical fluorescence quenching (qn), which was inhibited by addition of an uncoupler. These effects of H2O2 on qp and qn were inhibited by addition of KCN, an inhibitor of ascorbate peroxidase. The results suggest that H2O2 is reduced via ascorbate, and that the oxidized ascorbate is then reduced by linear electron flow contributing to photochemistry and thylakoid membrane energization. Evidence for function of pseudocyclic electron flow via the Mehler peroxidase reaction was obtained with only oxygen as an electron acceptor, as well as in the presence of oxaloacetate a natural electron acceptor in C4 photosynthesis. KCN decreased qp and PS II yield in the absence and presence of oxaloacetate and, in the former case, it severely reduced q_n. KCN also decreased pH formation across the thylakoid membrane based on its decrease in the light-induced quenching of 9-aminoacridine fluorescence, particularly in the absence of oxaloacetate. Antimycin A, an inhibitor of cyclic electron flow, also diminished pH formation. These results provide evidence for shared energization of thylakoid membranes by the Mehler peroxidase reaction, cyclic electron flow, and linear electron flow linked to the C4 pathway. 相似文献
4.
The effect of high CO2-concentration on photoacoustic signals from tobacco leaves is studied by means of a recently developed pulse modulation method which provides simultaneous information on photothermal and photobaric components in the millisecond time domain. High CO2-concentrations are found to induce large gas-uptake signals. Simultaneous measurements of chlorophyll fluorescence suggest that the uptake signals are correlated with energy-dependent fluorescence quenching. Very similar CO2-concentration dependencies are found in the absence and presence of methylviologen, which is known to catalyze O2-reduction, and in the presence of glyceraldehyde, which blocks Calvin cycle and photorespiration. It is suggested that the CO2-enhanced uptake signal is likely to reflect O2-uptake in the Mehler reaction. However, it is not ruled out that also rapid CO2-solubilisation or CO2-binding caused by light-induced stroma alkalisation are involved. Strong uptake is also induced when the CO2-concentration in the closed photoacoustic chamber increases due to dark-respiration. The consequences of these findings with respect to the interpretation of photoacoustic data (e.g., low-light effect) and to the regulatory role of O2-dependent electron flow are discussed. 相似文献
5.
Plastoquinone as a common link between photosynthesis and respiration in a blue-green alga 总被引:3,自引:0,他引:3
The role of plastoquinone in a thermophilic blue-green alga, Shynechococcus sp., was studied by measuring reduction kinetics of cytochrome 553 which was oxidized with red flash preferentially exciting photosystem I. Sensitivity of the cytochrome reduction to DBMIB indicates that cytochrome 553 accepts electrons from reduced plastoquinone. Plastoquinone is in turn reduced in cells without electrons from photosystem II, since DCMU, which inhibited methyl viologen photoreduction more strongly than DBMIB, failed to affect the cytochrome reduction. Participation of cyclic electron transport around photosystem I in cytochrome reduction in the presence of DCMU was excluded, because methyl viologen and antimycin A had no effect on the cytochrome kinetics. On the other hand, electron donation from endogenous substrates to plastoquinone was suggested from decreases in rate of the cytochrome reduction by dark starvation of cells and also from restoration of fast reduction kinetics by the addition of exogenous substrates to or by reillumination of starved cells.KCN, which completely suppressed respiratory O2-uptake, induced a marked acceleration of the cytochrome reduction in starved cells. The poison was less or not effective in stimulating the cytochrome reduction in more extensively starved or reilluminated cells.Results indicate that plastoquinone is functioning not only in the photosynthetic but also in the respiratory electron transport chain, thereby forming a common link between the two energy conservation systems of the blue-green alga.
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6.
G. K. Haverkamp H. Ranke C. G. Friedrich 《Applied microbiology and biotechnology》1995,44(3-4):514-518
The hydrogen-evolving reaction of the purified soluble NAD-linked hydrogenase of Alcaligenes eutrophus was used to determine kinetic parameters of the enzyme. The H2-evolving activity with methyl viologen as electron mediator was 20-fold as compared to that with NADH. In the assay with dithionite-reduced methyl viologen (K
m 0.7 mM) the hydrogenase was most active at a redox potential of –560 mV and exhibited a pH optimum of 7.0. The K
m for protons, the second substrate for H2 evolution, was 6.2 nM. With electrochemically reduced methyl viologen the pH optimum was shifted to pH 6.0. Double-reciprocal plots of reaction rates versus proton concentrations intercepted at the ordinate for different methyl viologen concentrations. At different pH values such an intercept was also observed with the dye as the varied substrate. The kinetic data are diagnostic for an ordered bisubstrate mechanism where both substrates are bound before the product H2 is released. Hydrogenase coupled to thylakoid membranes resulted in a constant H2 evolution rate over 6 h. The system appeared to be limited by the capacity of the thylakoid membranes. 相似文献
7.
Photophosphorylation capacity of stable spheroplast preparations of anabaena 总被引:2,自引:2,他引:0
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Spiller H 《Plant physiology》1980,66(3):446-450
Spheroplasts from Anabaena 7119 (formerly designated Nostoc muscorum) were prepared in the presence of serum albumin in 0.5 molar sucrose. Electron transport and photophosphorylation were preserved (> 70% of the maximum rate for 1 week). The pH profile of electron transport and photophosphorylation in the reactions H2O → NADP, H2O → methyl viologen, and H2O → ferricyanide shows that uncoupling by ammonia is small throughout and increases slightly with higher pH. ADP + Pi increased NADP reduction from H2O by 2.5-fold. The ratios of ATP formed per electron pair transported ranged from 0.9 to 1.5. Effects of catalase and superoxide dismutase on the overall O2 balance implicate pseudocyclic electron transport and phosphorylation. The quenching of 9-aminoacridine fluorescence indicates the formation of a Δ pH from 2 to 2.6 during illumination. This pH gradient is abolished by uncouplers; however, complete uncoupling is achieved only by 3-chlorocarbonyl cyanide phenylhydrazone or valinomycin + NH4+. In the presence of NH4+ alone, the membrane potential may act as the driving force for photophosphorylation. 相似文献
8.
When grown heterotrophically in the dark on enriched culture medium, the pigment-deficient strain of Scenedesmus obliquus, mutant C-6E, is uniquely characterized by a complete deficiency in carotenoids and chlorophyll b while retaining a low level of chlorophyll a which is exclusively utilized in photosystem I-type reactions. The strain lacks photosystem II activity but exhibits all PS-I reactions tested, including P700 redox reactions, photoreduction of CO2 with hydrogen as electron donor, and O2 uptake following methyl viologen reduction. The mutant contains 10 times more P700 per chlorophyll than the wild type and develops the pigment-protein complex of PS-I, CP-I. The action spectrum for methyl viologen reduction compares favorable to the low temperature absorption spectrum of whole cells. Both the chlorophyll fluorescence excitation and emission spectra of pigment-protein complexes derived from cells of C-6E show patterns typical of PS-I. The strain lacks the LHCs and CP-II as well as their respective apoproteins. The absence of carotenoids appears to prevent the development of the normal variety of pigment-protein complexes and the accumulation of Chl b. This inability is also expressed by the presence of only single stranded thylakoid membranes in the chloroplast of C-6E. When heterotrophically grown cells of this mutant are exposed to white light of 8 or 22 W m?2, 50% of its chlorophyll is lost by photooxidation within 4 or 1.5 hours, respectively. 相似文献
9.
Mehler-peroxidase reaction mediates zeaxanthin formation and zeaxanthin-related fluorescence quenching in intact chloroplasts 总被引:12,自引:4,他引:8
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Induction of zeaxanthin formation and the associated nonphotochemical quenching in iodoacetamide-treated, non-CO2-fixing intact chloroplasts of Lactuca sativa L. cv Romaine is reported. The electron transport needed to generate the required ΔpH for zeaxanthin formation and nonphotochemical quenching are ascribed to the Mehler-ascorbate peroxidase reaction. KCN, an inhibitor of ascorbate peroxidase, significantly affected these activities without affecting linear electron transport to methyl viologen or violaxanthin deepoxidase activity. At 1 millimolar KCN, zeaxanthin formation and ΔpH were inhibited 60 and 55%, respectively, whereas ascorbate peroxidase activity was inhibited almost totally. The KCN-resistant activity, which apparently was due to electron transport mediated by the Mehler reaction alone, however, was insufficient to support a high level of nonphotochemical quenching. We suggest that in vivo, as CO2 fixation becomes limiting, the Mehler-peroxidase reaction protects photosystem II against the excess light by supporting the electron transport needed for zeaxanthin-dependent nonphotochemical quenching and concomitantly scavenging H2O2. Ascorbate is essential for this process to occur. 相似文献
10.
Superoxide reduction as a mechanism of ascorbate-stimulated oxygen uptake by isolated chloroplasts 总被引:6,自引:0,他引:6
Addition of 1m ascorbate to isolated chloroplasts with methyl viologen (MV) as electron acceptor trebled the rate of oxygen uptake and decreased the ratio to a third of that with no ascorbate present. These effects of ascorbate were reversed by superoxide dismutase (SOD), which in the absence of ascorbate had little effect on O2 uptake or ratio. A chloroplast-associated SOD activity equivalent to 500 units/mg chlorophyll was detected. The effects of ascorbate and SOD on O2 uptake were similar in both coupled and uncoupled chloroplasts. The results are consistent with the hypothesis that ascorbate stimulates O2 uptake by reduction of superoxide, which is formed by autoxidation of the added electron acceptor (MV), and which dismutates in the absence of ascorbate. Ascorbate does not seem to stimulate O2 uptake by replacing water as the photosystem II donor. 相似文献
11.
Photosynthetic oxygen exchange in isolated cells and chloroplasts of c(3) plants 总被引:1,自引:12,他引:1
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Photosynthetic O2-production and photorespiratory O2-uptake were measured, using stable isotope techniques, in isolated intact leaf cells of the C3 plant Xanthium strumarium L., and isolated intact chloroplasts of Spinacia oleracea L (var. Yates 102). Considerable light dependent O2-uptake was observed in both systems, a proportion of which could be suppressed by CO2 (63% suppression in chloroplasts by 50 micromolar CO2, 58% in cells by 100 micromolar CO2 and 250 micromolar O2). At low O2, O2-uptake was CO2 insensitive. At high CO2 up to 19% of total electron flow was to O2 in cells and up to 14% in chloroplasts. O2-uptake showed inhibition by KCN (61% in cells, 35% in chloroplasts by 0.2 millimolar KCN). O2-uptake half saturated at 75 to 85 micromolar O2 in cells and 50 to 65 micromolar O2 in chloroplasts, at low CO2. The results are discussed in terms of the RuP2-oxygenase reaction and direct photoreduction of O2 via a Mehler reaction. 相似文献
12.
V. D. Kreslavski I. R. Fomina A. A. Kosobryukhov S. K. Herbert M. M. Babykin K. Y. Biel 《Biophysics》2007,52(2):204-210
Delayed Chl a fluorescence and the CO2-dependent O2 exchange were measured to assess the effect of oxidative stress inducers methyl viologen and benzyl viologen, cumene hydroperoxide, menadione, and H2O2 as well as high irradiance on the photosynthetic apparatus of Synechocystis sp. PCC 6803 wild type and its methyl viologen-resistant mutant Prq20 with impaired regulatory gene prqR. The extent of damage upon exposure to viologens proved much smaller in the mutant; the causes of this are analyzed. 相似文献
13.
A photoacoustic pulse-modulation technique is applied for the study of a CO2-stimulated gas uptake signal in leaves (Reising and Schreiber, Photosynthe Res 31: 227–238, 1992). It is shown that this uptake signal can be substantially suppressed by application of the carbonic anhydrase inhibitor, ethoxyzolamide, to leaf discs. This inhibitor does not affect the O2-evolution signal in air or the chlorophyll fluorescence induction pattern at high CO2, when non-saturating light intensities are used. On the basis of these findings it is concluded that at least a major part of the CO2-stimulated photoacoustic uptake signal results from light-modulated CO2-solubilisation catalysed by carbonic anhydrase. Modulated CO2-solubilisation appears likely to be induced by light driven H+-translocation from the stroma into the thylakoid lumen. Comparison of the induction patterns of chlorophyll fluorescence quenching and the uptake signal suggests a correlation between membrane energisation and CO2-uptake. The importance of O2-dependent electron flow as a major cause of membrane energisation is discussed. It is proposed that in the absence of CO2 the combination of Mehler- and ascorbate peroxidase reactions does not result in a photobaric signal, as O2-uptake and O2-evolution components cancel each other. Two main conclusions, which are of considerable importance for future practical applications of the photoacoustic method, are drawn from these findings: (1) When high CO2 is applied to leaves, the photobaric uptake component may provide a unique means of monitoring the function of stromal carbonic anhydrase in vivo. (2) Brief flushing of the photoacoustic cell with air may prevent the occurrence of an uptake signal, thus allowing a straight-forward deconvolution into photothermal and O2-evolution components. 相似文献
14.
In the absence of PSII, non-photochemical reduction of plastoquinones (PQs) occurs following NADH or NADPH addition in thylakoid membranes of the green alga Chlamydomonas reinhardtii. The nature of the enzyme involved in this reaction has been investigated in vitro by measuring chlorophyll fluorescence increase in anoxia and light-dependent O2 uptake in the presence of methyl viologen. Based on the insensitivity of these reactions to rotenone, a type-I NADH dehydrogenase (NDH-1) inhibitor, and their sensitivity to flavoenzyme inhibitors and thiol blocking agents, we conclude to the involvement of a type-II NADH dehydrogenase (NDH-2) in PQ reduction. Intact Chlamydomonas cells placed in anoxia have the property to produce H2 in the light by a Fe-hydrogenase which uses reduced ferredoxin as an electron donor. H2 production also occurs in the absence of PSII thanks to the existence of a non-photochemical pathway of PQ reduction. From inhibitors effects, we suggest the involvement of a plastidial NDH-2 in PSII-independent H2 production in Chlamydomonas. These results are discussed in relation to the absence of ndh genes in Chlamydomonas plastid genome and to the existence of 7 ORFs homologous to type-II NDHs in its nuclear genome. 相似文献
15.
A circadian rhythm in the rate of light-induced electron flow in three leguminous species 总被引:5,自引:4,他引:1
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Lonergan TA 《Plant physiology》1981,68(5):1041-1046
Three legume species, Pisum sativum L., Glycine max (L.), and Phaseolus vulgaris L., were grown in light-dark cycles and then maintained in constant dim light. During the constant conditions, chloroplasts were isolated throughout the day and assayed for various light-reaction activities. Similar results were found for all three species. The rate of whole-chain, light-induced electron flow (H2O to methyl viologen) was rhythmic over a 24-hour period provided an uncoupler of photophosphorylation was present. Chloroplasts varied in their response to uncouplers on a 24-hour basis and the per cent stimulation of electron flow was rhythmic. Neither PSII activity (H2O to DCPIP or light-induced pH changes in the presence of K3Fe(CN)6), PSI activity (DCPIPH2 ascorbate to methyl viologen) or the rate of oxidation of hydroquinone (TMQH2 to methyl viologen) could be identified as a rate-limiting step for the rate of electron flow. The capability to photophosphorylate as measured by a photosynthetic control assay was also constant with time. A rhythm in oxygen evolution was also observed with leaf mesophyll cell suspensions isolated from Pisum. The possible involvement of dynamic changes in the composition or configuration of the thylakoid membrane is discussed. 相似文献
16.
The use of O2 uptake as a valid assay for non-cyclic photosynthetic electron flow in membranes from Chlorobium limicola is discussed. It is recommended that methyl viologen, catalase and superoxide dismutase should be added to the experimental medium. The addition of methyl viologen more than doubled the rate of O2 uptake observed on illumination with 1 mM sulphide as donor. Superoxide dismutation was shown to be efficient under the experimental conditions by means of standard additions of potassium superoxide dissolved in dimethylsulphoxide. The highest rates of light stimulated O2 uptake were obtained with sulphide as electron donor, and approached 50 mol O2 · h-1 · mg bacteriochlorophyll c
-1 with 0.2 mM sulphide. The presence of 5 mM 2-mercaptoethanol or 3 mM sulphite as electron donor led to lower light stimulated rates of O2 uptake, while 5 mM thiosulphate had little effect. The rates were insensitive to uncoupler. The light stimulated O2 uptake with 0.2 mM sulphide as donor was 20–30% inhibited by 10 M antimycin A and 50 M cyanide.Abbreviations APS
Adenosine 5-phosphosulphate
- FCCP
carbonylcyanide-p-trifluoromethoxyphenylhydrazone
- HEPES
4-(2-hydroxyethyl)-1-piperazineethanesulphonic acid
- MeV
methyl viologen
- P-840
the photoreactive bacteriochlorophyll 相似文献
17.
Synechococcus sp. RF-1, a unicellular N2-fixing cyanobacterium, can grow photosynthetically and diazotrophically in continuous light. How the organism protects its
nitrogenase from damage by oxygen is unclear. In cyanobacerial cells, electron transport carriers associated with photosynthesis
and respiration are all on the thylakoid membranes and share some common components, including plastoquinone pool and cytochrome
b
6
f complex, and the pathways are interacting with each other. In this work, a pulse amplitude modulation (PAM) fluorometer (PAM-101)
and an O2 electrode are used simultaneously to study the chlorophyll a fluorescence and to monitor O2 exchanges in Synechococcus sp. RF-1 cells. At the CO2 compensation point, the photochemical quenching activity remained high unless the O2 was exhausted by the glucose oxidase system (GOS). It indicates that in addition to CO2, O2 can also act as electron acceptor to receive electrons derived from QA. Studies with various inhibitors of the electron transport chain demonstrated that 3-(3,4-dichlorophenyl)-1,1-dimethylurea
(DCMU), 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB) and salicylhydroxamic acid (SHAM) inhibited the photoreduction of O2, while glycolaldehyde, disalicylidenepropanediamine (DSPD), methyl viologen (MV) and KCN did not. These results imply that
a KCN-resistant and SHAM-sensitive oxidase transfers electrons generated from Photosystem II to O2 between cytochrome b
6
f complex and ferredoxin. When SHAM blocked this alternative electron transport pathway, the dinitrogen-fixing activity decreased
significantly. The results indicate that a novel oxidase may function as an intracellular O2-scavenger in Synechococcus sp. RF-1 cells.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
18.
Uncouplers stimulate photosynthesis in intact chloroplasts by enhancing light-activation of enzymes regulated by the ferredoxin-thioredoxin system 总被引:3,自引:3,他引:0
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Some uncouplers stimulate CO2-dependent O2 evolution by intact spinach chloroplasts at pH 8.6. This effect is not due to alkalinization of the stroma. The stimulation is observed only when photosynthesis has been partly inhibited by the presence of H2O2, generated in a Mehler-type reaction by the broken chloroplasts which always contaminate the intact chloroplast preparations. The addition of methyl viologen increases the Mehler-type reaction and results in greater inhibition of photosynthesis. The addition of excess catalase stimulates photosynthesis by preventing accumulation of H2O2. The uncouplers stimulate photosynthesis primarily by enhancing the light-activation of enzymes that are regulated by the ferredoxin-thioredoxin system, and this effect results from the influence of the uncouplers on the redox poising of the ferredoxin in the intact chloroplasts. 相似文献
19.
Günter A. Peschek 《BBA》1979,548(2):203-215
1. The oxyhydrogen reaction of Anacystis nidulans was studied manometrically and polarographically in whole cells and in cell-free preparations; the activity was found to be associated with the particulate fraction.2. Besides O2, the isolated membranes reduced artificial electron acceptors of positive redox potential; the reactions were unaffected by O2 levels <10–15%; aerobically the artificial acceptors were reduced simultaneously with O2.3. H2-supported O2 uptake was inhibited by CO, KCN and 2-n-heptyl-8-hydroxyquinoline-N-oxide. Inhibition by CO was partly reversed by strong light. Uncouplers stimulated the oxyhydrogen reaction.4. The kinetic properties of O2 uptake by isolated membranes were the same in presence of H2 and of other respiratory substrates.5. Low rates of H2 evolution by the membrane preparations were found in presence of dithionite; methyl viologen stimulated the reaction.6. The results indicate that under certain growth conditions Anacystis synthesizes a membrane-bound hydrogenase which appears to be involved in phosphorylative electron flow from H2 to O2 through the respiratory chain. 相似文献
20.
Günter A. Peschek 《BBA》1979,548(2):187-202
1. Anaerobic hydrogenase activity in whole cells and cell-free preparations of H2-induced Anacystis was studied both manometrically and spectrophotometrically in presence of physiological and artificial electron acceptors.2. Up to 90% of the activity measured in crude extracts were recovered in the chlorophyll-containing membrane fraction after centrifugation (144 000 × g, 3 h).3. Reduction of methyl viologen, diquat, ferredoxin, nitrite and NADP by the membranes was light dependent while oxidants of more positive redox potential were reduced also in the dark.4. Evolution of H2 by the membranes was obtained with dithionite and with reduced methyl viologen; the reaction was stimulated by detergents.5. Both uptake and evolution of H2 were sensitive to O2, CO, and thiol-blocking agents. The H2-dependent reductions were inhibited also by the plastoquinone antagonist dibromothymoquinone, while the ferredoxin inhibitor disalicylidenepropanediamine affected the photoreduction of nitrite and NADP only. 3-(3,4-Dichlorophenyl)-1,1-dimethylurea did not inhibit any one of the H2-dependent reactions.6. The results present evidence for a membrane-bound ‘photoreduction’ hydrogenase in H2-induced Anacystis. The enzyme apparently initiates a light-driven electron flow from H2 to various low-potential acceptors including endogenous ferredoxin. 相似文献