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1.
The non-ionic detergent, Brij 58, has been shown to specifically lyse the cytoplasmic membrane of Escherichia coli. This communication examines the electron transport system in membrane fractions prepared from such lysates and compares this system to those prepared by mechanical procedures. 1. 1. The particulate fraction contained all of the respiratory carriers demonstrable in whole cells in essentially the same ratios although enriched by 3–5-fold over their concentration in whole cells. 2. 2. Succinate, formate, and NADH but not glutamate, malate, or dihydroorotate were actively oxidized by the particulate fraction. 3. 3. With the exception of the formate oxidase system which appeared to utilize a system bypassing flavoprotein and cytochrome b1, the other enzymatic activities appeared to function primarily through normal electron transport routes. 4. 4. The NADH oxidase and succinoxidase systems were sensitive to inhibition by 2-n-heptyl-4-hydroxyquinoline-N-oxide and antimycin A. The results suggest that these inhibitors function at the level of cytochrome b1. 5. 5. All three activities were sensitive to complete inhibition by CN−. 6. 6. The results obtained from inhibitor studies coupled with the results obtained from examination of steady state, anaerobic, and chemical reduction of the respiratory pigments permitted a scheme for electron flow to be proposed.
Abbreviations: HOQNO; 2-n-heptyl-4-hydroxyquinoline-N-oxide 相似文献
2.
Chromatophores isolated from the purple sulfur bacterium Chromatium and the green sulfur bacterium Chlorobium exhibit absorbance changes in the cytochrome -band region consistent with the presence of a b-type cytochrome. Cytochrome content determined by reduced minus oxidized difference spectra and by heme analysis suggests that each bacterium contains one cytochrome b per molecule of photochemically active bacteriochlorophyll (reaction-center bacteriochlorophyll). The b-type cytochrome in Chromatium has an -band maximum at 560 nm and a midpoint oxidation-reduction potential of −5 mV at pH 8.0. The b-type cytochrome in Chlorobium has an -band maximum at 564 nm and an apparent midpoint oxidation-reduction potential near −90 mV. Chromatophores isolated from both Chromatium and Chlorobium cells catalyze a photoreduction of cytochrome b that is enhanced in the presence of antimycin A. Antimycin A and 2-n-heptyl-4-hydroxyquinoline-N-oxide inhibit endogenous (but not phenazine methosulfate-mediated) cyclic photophosphorylation in Chromatium chromatophores and non-cyclic electron flow from Na2S to NADP in Chlorobium chromatophores. These observations suggest that b-type cytochromes may function in electron transport reactions in photosynthetic sulfur bacteria. 相似文献
3.
A procedure is described for preparing particles from cells of Micrococcus denitrificans which were broken osmotically after treatment with lysozyme. 1. 1. The preparations catalysed ATP synthesis coupled to O2 uptake or NO3− reduction. With NADH or succinate as the electron donors the P:O ratios were about 1.5 and 0.5, respectively; and the P:NO3− ratios were about 0.9 and 0.06, respectively. 2. 2. Addition of ADP or Pi to the reaction mixture increased the rates of NADH-dependent O2 uptake and NO3− reduction. Addition of 1 mM 2,4-dinitrophenol, which inhibited phosphorylation by 50–60%, increased the basal rates of electron transport. 3. 3. Evidence derived from spectrophotometry and from the differential inhibition by antimycin A of O2 and NO3− reduction leads to the conclusion that the nitrate reductase interacted with the respiratory chain in the region of the b-type cytochrome, and that the c-type cytochrome present was not involved in the reduction of NO3− to NO2−.
Abbreviations: TMPD; tetramethyl-p-phenylenediamine 相似文献
4.
The formation of nitrite reductase and cytochrome c in Micrococcus denitrificans was repressed by O 2. The purified nitrite reductase utilized reduced forms of cytochrome c, phenazine methosulphate, benzyl viologen and methyl viologen, respectively, as electron donors. The enzyme was inhibited by KCN, NaN 3 and NH 2OH each at 1 mM, whereas CO and bathocuproin, diethyl dithiocarbamate, o-phenanthroline and ,'-dipyridyl at 1 mM concentrations were relatively ineffective. The purified enzyme contains cytochromes, probably of the c and a2 types, in one complex. A Km of 46 μM for NO 2− and a pH optimum of 6.7 were recorded for the enzyme. The molecular weight of the enzyme was estimated to be around 130000, and its anodic mobility was 6.8·10 −6 cm 2·sec −1·V −1 at pH 4.55. The most highly purified nitrite reductase still exhibited cytochrome c oxidase activity with a Km of 27 μM for O2. This activity was also inhibited by KCN, NaN3 and NH2OH and by NO2−. A constitutive cytochrome oxidase associated with membranes was also isolated from cells grown anaerobically with NO2−. It was inhibited by smaller amounts of KCN, NaN3 and NH2OH than the cytochrome oxidase activity of the nitrite reductase enzyme and also differed in having a pH optimum of about 8 and a Km for O2 of less than 0.1 μM. Spectroscopically, cytochromes b and c were found to be associated with the constitutive oxidase in the particulate preparation. Its activity was also inhibited by NO2−. The physiological role of the cytochrome oxidase activity associated with the purified nitrite reductase is likely to be of secondary importance for the following reasons: (a) it accounts for less than 10% of total cytochrome c oxidase activity of cell extracts; (b) the constitutive cytochrome c oxidase has a smaller Km for O2 and would therefore be expected to function more efficiently especially at low concentrations of O2. 相似文献
5.
1. 1. The superoxide anion radical (O2−) reacts with ferricytochrome c to form ferrocytochrome c. No intermediate complexes are observable. No reaction could be detected between O2− and ferrocytochrome c. 2. 2. At 20 °C the rate constant for the reaction at pH 4.7 to 6.7 is 1.4 · 106 M−1 · s−1 and as the pH increases above 6.7 the rate constant steadily decreases. The dependence on pH is the same for tuna heart and horse heart cytochrome c. No reaction could be demonstrated between O2− and the form of cytochrome c which exists above pH ≈ 9.2. The dependence of the rate constant on pH can be explained if cytochrome c has pKs of 7.45 and 9.2, and O2− reacts with the form present below pH 7.45 with k = 1.4 · 106 M−1 · s−1, the form above pH 7.45 with k = 3.0 · 105 M−1 · s−1, and the form present above pH 9.2 with k = 0. 3. 3. The reaction has an activation energy of 20 kJ mol−1 and an enthalpy of activation at 25 °C of 18 kJ mol−1 both above and below pH 7.45. It is suggested that O2− may reduce cytochrome c through a track composed of aromatic amino acids, and that little protein rearrangement is required for the formation of the activated complex. 4. 4. No reduction of ferricytochrome c by HO2 radicals could be demonstrated at pH 1.2–6.2 but at pH 5.3, HO2 radicals oxidize ferrocytochrome c with a rate constant of about 5 · 105–5 · 106 M−1 · s−1
. 相似文献
6.
The bifunctional hypoxia-specific cytotoxin RB90745, has a nitroimidazole moiety attached to an imidazo[1,2,- a]quinoxaline mono- N-oxide with a spacer/linking group. The reduction chemistry of the drug was studied by pulse radiolysis using the one electron reductant CO 2˙-. As N-oxides and nitro compounds react with CO 2˙- at diffusion controlled rates, initial reaction produced a mixture of the nitro radical (λ max 410 nm) and the N-oxide radical (λ max 550 nm) in a few microseconds. Subsequently an intramolecular electron transfer (IET) was observed ( k = 1.0 ± 0.25 × 10 3 s -1 at pH 5-9), from the N-oxide to the more electron-affinic nitro group. This was confirmed by the first order decay rate of the radical at 550 nm and formation at 410 nm, which was independent of both the concentration of the parent compound and the radicals. The rates of electron transfer and the decay kinetics of the nitro anion radicals were pH dependent and three different pK aS could be estimated for the one electron reduced species: 5.6 (nitroimidazole group) and 4.3, and 7.6 ( N-oxide function). The radicals react with oxygen with rate constants of 3.1 × 10 7 and 2.8 × 10 6 dm 3 mol -1 s -1 observed at 575 nm and 410 nm respectively. Steady state radiolysis studies indicated four electron stoichiometry for the reduction of the compound. 相似文献
7.
1. Difference spectra, at room and liquid N 2 temperatures, of S 2O 42−-, and NO 2−-reduced intact cells and cell-free preparations of Nitrobacter agilis demonstrated the presence of cytochromes of the c- and a-types. Reduction of cytochromes by succinate, and to a limited extent, by NADPH also occurred, provided KCN (0.1 mM) was also present. 2. A particulate, heat-labile nitrite oxidase having an absolute requirement for O2 was prepared from N. agilis cells using sonic oscillation and differential centrifugation. The particles also possessed NADH oxidase, succinoxidase, formate oxidase and traces of NADPH oxidase activity. The stoichiometry of the nitrite oxidase reaction approached the theoretical value of 2 moles of NO2− consumed per mole of O2 consumed. The pH optimum of the nitrite oxidase system shifted to progressively more alkaline values as the NO2− concentration was increased, changing from a pH value of 6.8 at 0.6 mM KNO2 to pH 8.0 at 0.01 M KNO2 with apparent Km's of 0.2 and 1.2 mM NO2−, respectively. Computations of the HNO2 concentrations present under the above conditions showed an approx. 500-fold greater affinity for HNO2 which was independent of pH, suggesting the involvement of HNO2 as both a substrate and an inhibitor (at higher concentrations) of the nitrite oxidase system. The marked inhibition by NaN3, NaCN and Na2S, as well the light-reversible inhibition by CO, indicated the presence of cytochrome oxidase which was subsequently characterized. NO2− proved to be a competitive inhibitor of the nitrite oxidase system. 3. The particulate preparation also possessed a heat-labile nitrite-cytochrome c reductase activity which was energy independent and routinely measured under anaerobic conditions. As in the case of nitrite oxidase, the affinity of the enzyme for NO3− increased as the pH was lowered, but the pH optimum remained unaffected. In terms of calculated HNO2 concentration an approximately constant Km of about 0.2 μM was estimated at the several pH's examined. The inhibition by NO3− was shown to be competitive. The marked sensitivity of the reductase to several metal-binding agents implicated a metal component in the electron transport chain at the site prior to cytochrome c. 4. The membrane-like composition of the nitrite oxidase system is indicated. 相似文献
8.
The reduction of ferricytochrome c by O 2− and CO 2− was studied in the pH range 6.6–9.2 and Arrhenius as well as Eyring parameters were derived from the rate constants and their temperature dependence. Ionic effects on the rate indicate that the redox process proceeds through a multiply-positively charged interaction site on cytochrome c. It is shown that the reaction with O 2− and correspondingly with O 2 of ferrocytochrome c) is by a factor of approx. 10 3 slower than warranted by factors such as redox potential. Evidence is adduced to support the view that this slowness is connected with the role of water in the interaction between O 2−/O 2 and ferri-ferrocytochrome c in the positively charged interaction site on cytochrome c in which water molecules are specifically involved in maintaining the local structure of cytochrome c and participate in the process of electron equivalent transfer. 相似文献
9.
The X-ray structure is reported for the complex Cu 2(medpco-2H)Cl 2, (medpco = N, N′-bis- N, N-dimethylaminoethyl)pyridine-2,6-dicarboxamide 1-oxide. The complex is triclinic,
, a=8.313(4), B=11.403(5), C=11.611(3) Å, =91.66(3), β=108.99(4), γ=109.60(3)° and Z=2. The deprotonated ligand (medpco-2H) 2− acts as a binulceating ligand, producing an N-oxide-bridged complex. Each copper in Cu 2(medpco-2H)Cl 2 is five-coordinate, being coordinated by a bridging N-oxide oxygen, a deprotonated amide nitrogen, a tertiary amine nitrogen and two bridging chlorides. The complex does not exhibit significant magnetic interaction, and this may be the result of distortion of the bridging geometry from planarity. A range of other, apparently N-oxide-bridged, complexes of the type Cu 2(medpco-2H)X 2 is reported. The complex Cu 2(medpco-2H)Br 2·H 2O is strongly antiferromagnetic, with magnetic data closely fitting the expected binuclear structure. 相似文献
10.
The survival of Leishmania, which encounter drastic changes of environment during their life-cycle, requires regulation and control of ionic concentrations within the cell. We analysed the influence of growth stage, ionic composition of the medium, heat and acidic stress on 86Rb + influx in L. infantum promastigetes. Proliferating promastigotes exibited faster and higher 86Rb + uptake than stationary cells. Cl − anion did not have any effect, but in the presence of physiological concentration of HCO 3−, 86Rb + uptake was significantly increased. This enhancing effect was only partially inhibited by N,N′-dicyclohexylcarbodiimide (DCCD), a blocker of ion-translocating ATPases. 86Rb + influx was abolished by N-ethylmaleimide (NEM), indicating a major contribution of plasma membrane transporters. Heat shock and acidic shock notably decreased 86Rb + influx. Our data provide indirect evidence that an energy-dependent system which brings K + in, such as K +/H +-ATPase evidenced by Jiang et al. (1994), is active in Leishmania in different environments. Mechanism(s) other than ion-translocating ATPase occur, at least in the presence of HCO 3−, and their contribution to K + pathways varies in different environmental conditions. 相似文献
11.
1. Circular dichroism spectra of the cytochromes in membrane fragments derived from sonicated beef heart mitochondria have been obtained in the wavelength region 400–480 nm in which the major absorbance maxima of the heme prosthetic groups are found. 2. 2. Cytochrome oxidase in the mitochondrial membrane fragments has a band of positive ellipticity at 426 nm in the oxidized form and a pronounced band of positive ellipticity at 445 nm in the reduced form. The reduced-minus-oxidized difference molar ellipticity at 445 nm, Δ[θ]445 is 3.0·105 degree·cm−2·dmole−1 heme a for membrane-bound oxidase compared to 1.6·105 degree·cm−2·dmole−1 heme a for the purified oxidase. The membrane-bound oxidase in the reduced form also appears to have a band of negative ellipticity at 426 nm not found in the purified oxidase. 3. 3. When reduced with succinate in the presence of cyanide and oxygen, cytochrome oxidase in the membrane fragments has a positive band at 442 nm very similar to that observed with the purified oxidase. 4. 4. Cytochrome c, which has a positive band at 426 nm in the purified form when reduced, appears to have a negative band at this wavelength in the mito-chondrial membrane fragments which contributes to the pronounced negative band at 426 nm observed in the membrane fragments reduced with succinate in anaerobiosis. There is no evidence for a contribution to the CD spectra of the membrane fragments from cytochrome c1 or from cytochrome b561 in either the oxidized or the reduced form. 5. 5. Cytochrome b566 in the mitochondrial membrane fragments has no detectable CD spectrum in the oxidized form, but has a small positive band at 427 nm and a small negative band at 436 nm in the reduced form. The same CD spectrum is observed with cytochrome b566 reduced with succinate in the presence of antimycin A or 2-heptyl-4-hydroxyquinoline-N-oxide. The same increase in positive ellipticity is observed at 427 nm in the mitochondrial membrane fragments, treated with oligomycin to restore energy coupling, when cytochrome b566 is reduced with succinate in the energized membrane, as is observed in the inhibitor-treated membrane fragments. The absence of a pronounced conformational change in cytochrome b566 on energization, as revealed by its CD spectrum, favors the concept that its reduction by succinate in the energized state is due to reversed electron transport rather than an intrinsic shift in the cytochrome's midpoint redox potential.
Abbreviations: HOQNO, 2-heptyl-4-hydroxy quinoline-N-oxide; PMS, phenazine methosulfate 相似文献
12.
1. The nitrite oxidase particles obtained by sonic oscillation of Nitrobacter agilis cells also possessed appreciable formate oxidase activity, ranging from about 25 to 50% of the nitrite oxidase activity depending upon the N. agilis strain. Both activities distributed themselves in the same pattern and proportions during differential centrifugation, and resided solely in the pellet resulting from high-speed centrifugation. 2. Difference spectra of formate-reduced particles or intact cells demonstrated the presence of cytochromes of the c- and a-types like those of the NO2−-reduced material. Under anaerobic conditions NO3− or fumarate acted as an alternate electron acceptor in place of O2 in formate oxidation. Under aerobic conditions increasing NO3− concentrations resulted in (a) an increased role of NO3− as a terminal electron acceptor compared to O2, (b) a greater total enzymatic transfer of electrons from formate than if O2 were the sole electron acceptor, and (c) a partial inhibition of O2 uptake suggestive of a competition for electrons by the two acceptors. The formate oxidase system failed to catalyze consistently the transfer of electrons to either added mammalian cytochrome c or Fe(CN)63−. The marked sensitivity of the system to certain inhibitors implicated cytochrome oxidase as an integral part of the formate oxidase. The system was also inhibited significantly by a variety of chelating agents, indicating a metal component in the formate dehydrogenase or early portion of the electron transfer sequence. 3. The stoichiometry of the formate oxidase system was shown to approach the theoretical value of 2 moles of CO2 evolved per mole of O2 or per 2 moles of formate consumed. 4. To a limited extent, phosphorylation occurred concomittantly with the oxidation of formate in the presence of the cell-free particulate system. 相似文献
13.
The formation of membrane potential in sonicated particles of an aerobic bacterium, Micrococcus lysodeikticus, and of pea chloroplasts has been demonstrated To detect membrane potential, the responses of synthetic penetrating anions of phenyl dicarbaundecaborane (PCB−), tetraphenyl boron and anilinonaphthalene-sulfonate (ANS−) were studied. It was found that oxidation of NADH, succinate, malate, and lactate by oxygen in particles of M. lysodeikticus is coupled with anion uptake and ANS- fluorescence enhancement, the fact testifying to the formation of membrane potential (“plus” inside particles). Uncouplers, cyanide and heptyl-hydroxyquinoline N-oxide prevent and reverse respiration-induced anion responses. Cyanide-resistant oxygen uptake is not coupled with ion fluxes. Ion responses are inhibited by acceptors competing with oxygen for electrons, such as Q0, menadione, and also ferricyanide when malate or succinate (but not lactate) are oxidized. In cyanide-treated particles, reduction of ferricyanide by lactate, but not by malate, supports some anion transport. In contrast to respiration, ATP does not actuate ion fluxes in M. lysodeikticus particles competent in respiratory phosphorylation. In sonicated particles of pea chloroplasts, light-induced anion uptake can be observed. Switching off light results in the efflux of anions accumulated on illumination. Again, ATP does not induce any anion response, although the system of photophosphorylation is active under the same conditions. It is concluded that formation of a membrane potential in particles of M. lysodeikticus and pea chloroplasts (plus inside) can be actuated by electron transfer but not ATP hydrolysis. The ineffectiveness of ATP seems to be a result of irreversibility, rather than damage, of the energy transfer chain; a property in which coupling mechanisms of M. lysodeikticus and chloroplasts differ from those of animal mitochondria and Rhodospirillum rubrum chromatophores. 相似文献
14.
We have previously shown that crystals of calcium oxalate (COM) elicit a superoxide (O 2−) response from mitochondria. We have now investigated: (i) if other microparticles can elicit the same response, (ii) if processing of crystals is involved, and (iii) at what level of mitochondrial function oxalate acts. O 2− was measured in digitonin-permeabilized MDCK cells by lucigenin (10 μM) chemiluminescence. [ 14C]-COM dissociation was examined with or without EDTA and employing alternative chelators. Whereas mitochondrial O 2− in COM-treated cells was three- to fourfold enhanced compared to controls, other particulates (uric acid, zymosan, and latex beads) either did not increase O 2− or were much less effective (hydroxyapatite +50%, p < 0.01), with all at 28 μg/cm 2. Free oxalate (750 μM), at the level released from COM with EDTA (1 mM), increased O 2− (+50%, p < 0.01). Omitting EDTA abrogated this signal, which was restored completely by EGTA and partially by ascorbate, but not by desferrioxamine or citrate. Omission of phosphate abrogated O 2−, implicating phosphate-dependent mitochondrial dicarboxylate transport. COM caused a time-related increase in the mitochondrial membrane potential (Δψ m) measured using TMRM fluorescence and confocal microscopy. Application of COM to Fura 2-loaded cells induced rapid, large-amplitude cytosolic Ca 2+ transients, which were inhibited by thapsigargin, indicating that COM induces release of Ca 2+ from internal stores. Thus, COM-induced mitochondrial O 2− requires the release of free oxalate and contributes to a synergistic response. Intracellular dissociation of COM and the mitochondrial dicarboxylate transporter are important in O 2− production, which is probably regulated by Δψ m. 相似文献
15.
The perchlorate (ClO 4−)-respiring organism, strain perc1ace, can grow using nitrate (NO 3−) as a terminal electron acceptor. In resting cell suspensions, NO 3− grown cells reduced ClO 4−, and ClO 4− grown cells reduced NO 3−. Activity assays showed that nitrate reductase (NR) activity was 1.31 μmol min −1 (mg protein) −1 in ClO 4− grown cells, and perchlorate reductase (PR) activity was 4.24 μmol min −1 (mg protein) −1 in NO 3− grown cells. PR activity was detected within the periplasmic space, with activities as high as 14 μmol min −1 (mg protein) −1. The NR had a pH optimum of 9.0 while the PR had an optimum of 8.0. This study suggests that separate terminal reductases are present in strain perclace to reduce NO 3− and ClO 4−. 相似文献
16.
A fed-batch process was developed for high cell density culture of the diatom Nitzschia laevis for enhanced production of eicosapentaenoic acid (EPA). Firstly, among the various medium components, glucose (Glu) was identified as the limiting substrate while nitrate (NO 3−), tryptone (Tr) and yeast extract (Ye) were found to promote cell growth by enhancing specific growth rate. Therefore, these components were considered essential and were included in the feed medium for subsequent fed-batch cultivation. With the optimized ratio of NO 3−:Tr:Ye being 1:2.6:1.3 (by weight), the relative proportions of glucose to the nitrogen sources in the feed were investigated. The optimal ratios of Glu:NO 3− for specific growth rate and EPA productivity were both determined to be 32:1 (by weight). Finally, based on the residual glucose concentration in the culture, a continuous medium feeding strategy for fed-batch fermenter cultivation was developed, with which, the maximal cell dry weight and EPA yield obtained were 22.1 g l −1 and 695 mg l −1, respectively, which were great improvements over those of batch cultures. 相似文献
17.
A novel nutrient removal/waste heat utilization process was simulated using semicontinuous cultures of the thermophilic cyanobacterium Fischerella. Dissolved inorganic carbon (DIC)-enriched cultures, maintained with 10 mg l −1 daily productivity, diurnally varying temperature (from 55°C to 26–28°C), a 12:12 light cycle (200 μE sec −1 m −2) and 50% biomass recycling into heated effluent at the beginning of each light period, removed > 95% of NO 3− + NO 2−−N, 71% of NH 3-N, 82% of PO 43− −P, and 70% of total P from effluent water samples containing approximately 400 μg l −1 combined N and 60 μg l −1 P. Nutrient removal was not severely impaired by an altered temperature gradient, doubled light intensity, or DIC limitation. Recycling 75% of the biomass at the end of each light period resulted in unimpaired NO 3− + NO 2− removal, 38–45% P removal and no net NH 3 removal. Diurnally varying P removal, averaging 50–60%, and nearly constant > 80% N removal, are therefore projected for a full-scale process with continuous biomass recycling. 相似文献
18.
A field study measured the rate of soil mineral N supply and its effects on plant biomass and N accumulation in a 13-year-old, naturally regenerating, calcareous grassland. Gross rates of N mineralisation (2 μg g −1 day −1, i.e. 0.69 kg ha −1 day −1), assessed using 15N pool dilution, were at the lower end of the range previously reported for grasslands. Weekly additions of liquid N fertiliser ([NH 4] 2SO 4, NH 4NO 3 or KNO 3) and, to a lesser extent the addition of water, increased plant growth substantially, demonstrating that the primary constraint to plant growth was low N availability. In plants that had received NO 3−, the activity of the inducible enzyme nitrate reductase in shoots initially increased in proportion to the amount of NO 3− supplied. However, as above-ground herbage accumulated, nitrate reductase activity declined to similar low levels in all treatments, despite the continuance of the constant NO 3− additions. The decline in NR specific activity reflected declining tissue NO 3− concentrations, although total plant NRA may have remained constant during the period of study. The study has shown that plant growth is limited by low N mineralisation rates and indeed the soil is a sink for much added N. Low water availability provides an additional constraint on N mineralisation in this calcareous grassland soil. Any disturbances in the N cycle which increase the availability of mineral N will result in a substantial increase in plant growth within this ecosystem. 相似文献
19.
The particulate fraction of Rhodopseudomonas viridis when supplied with succinate catalyses the reduction of NAD + by light; this reaction is inhibited by uncouplers of oxidative phosphorylation but not by oligomycin. Formation of NADH takes place in the dark when ATP or PP i is supplied. Both light and dark reactions are inhibited by valinomycin and nigericin, when added together, but not by either separately. NADH formation in R. viridis appears to take place by an energy-dependent reversal of electron flow and energy may be conserved in the form of a membrane potential. The addition of ATP caused the oxidation of both C553 and C558 in chromatophores; carbonylcyanide p-trifluoromethoxyphenylhydrazone and oligomycin abolished this oxidation. The NAD+ and NADH concentrations at equilibrium in the light-dependent reaction were determined and the oxidation-reduction potential of this couple calculated. From this value it was calculated that under these experimental conditions the energy requirement to form NADH from the succinate/fumarate couple at Eh = o V was 9.4 kcal. Particles of R. viridis contained an active transhydrogenase, driven by either light or ATP, that was sensitive to uncouplers of oxidative phosphorylation; the light-driven reaction was insensitive to oligomycin and was inhibited by antimycin A and 2-heptyl-4-hydroxyquinone-N-oxide. R. viridis did not grow aerobically but particles contained NADH oxidase activity that was cyanide sensitive. There was no spectroscopic evidence for cytochromes of the b-type in reduced-minus-oxidised spectra of particles or in pyridine haemochrome spectra of whole cells. 相似文献
20.
Phaseolus vulgaris L. cv. Kinghorn Wax seedlings, supplied with nutrient solution containing either 0 or 5 mM nitrate as sole N source, were exposed to 0.25 μl/l NO 2 for 6 hr each day for 10 days at continuous photosynthetic photon flux (PPF) of 100, 300, 500 or 700 μmol m −2 sec −1. There was a significant interaction of PPF and nitrate. Shoot and root dry weights increased with increasing PPFs only when nitrate was supplied. The main effects of NO 2 on plant growth were significant; none of the interactions involving NO 2 were significant. Exposure to NO 2 decreased shoot and root dry weight in both the presence and absence of nutrient N and at all PPF levels. All interactions were significant for in vitro leaf nitrate reductase activity (NRA), which increased markedly at PPFs above 100 μmol m −2 sec −1 when nitrate was supplied. Treatment with NO 2 strongly inhibited enzyme activity in the presence of nitrate, particularly at the 300 μmol m −2 sec −1 PPF level. These experiments demonstrated that PPF level does not modify the effect of NO 2 on growth but does have a major effect on NRA and on NO 2 effects on NRA in the presence of nutrient nitrate. 相似文献
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