共查询到20条相似文献,搜索用时 15 毫秒
1.
9-Aminoacridine has been used to monitor the intrathylakoid pH of photosynthetically competent intact chloroplasts. Values obtained from 9-aminoacridine accumulation in the chloroplasts must be corrected for light-dependent binding of 9-aminoacridine to the thylakoid membranes. During nitrite reduction by intact chloroplasts, the intrathylakoid proton concentration increased. It decreased somewhat during CO2 reduction. However, low concentrations of uncoupling amines such as NH3 or cyclohexylamine, which rapidly penetrated the chloroplast envelope and decreased the intrathylakoid proton concentration, failed to reduce, and actually stimulated, rates of CO2-dependent oxygen evolution even under rate-limiting light. In contrast, low concentrations of carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) OR NIGERICIN, WHICH INHIBITED CO2 reduction, even appeared to increase the intrathylakoid proton concentration. As indicated by measurements of the 515 nm signal of the chloroplasts, the light-induced membrane potential was not much affected by low concentrations of the uncoupling amines, but was decreased by FCCP and by high concentrations of the amines. Even in the presence of high concentrations of NH4C1, ATP/ADP ratios of illuminated chloroplasts remained far above the ratios observed in the dark. In contrast, low concentrations of FCCP were sufficient to reduce ATP/ADP ratios to the dark value even under high intensity illumination. The observations are difficult to explain within the framework of the chemiosmotic hypothesis as presently discussed. 相似文献
2.
In the presence of nitrite or oxaloacetate, intact chloroplasts evolved oxygen at a significant rate for the initial 1 to 2 min of illumination. Subsequently, oxygen evolution was suppressed progressively. The suppressed oxygen evolution was stimulated strikingly by NH4Cl. The results indicate that coupled electron flow in intact chloroplasts is controlled in the light, and the control is released by NH4Cl. However, at low concentrations, NH4Cl was not an effective uncoupler of photophosphorylation in intact chloroplasts. Intrachloroplast ATP levels and ATP/ADP ratios were not significantly influenced by NH4Cl. In contrast, the quenching of 9-aminoacridine fluorescence, which can be used to indicate the intrathylakoid pH in intact chloroplasts, was reduced drastically even by low concentrations of NH4Cl. This suggests that the chloroplast phosphorylation potential is not in equilibrium with the proton gradient. In coupled chloroplasts, the intrathylakoid pH was lower in the light with nitrite than with oxaloacetate as electron acceptor. Electron flow was also more effectively controlled in chloroplasts illuminated with nitrite than with oxaloacetate. It is concluded that the intrathylakoid pH, not the phosphorylation potential, is a factor in the control of the rate of electron flow in intact chloroplasts.Abbreviations CCCP
carbonylcyanide-m-chlorophenylhydrazone
- OAA
oxalo-acetate
- MES
2-(N-morpholino)-ethanesulfonic acid
- HEPES
N-2-hyroxyethylpiperazine-N-2-ethanesulfonic acid
Postal address 相似文献
3.
Combinations of low concentrations of carbonyl cyanide p-trifluoromethoxyphenylhy-drazone (FCCP) with suboptimal concentrations of Dio-9, phloridzin, ajmaline, and dihydrodiscarine B synergistically inhibited cyclic and noncyclic photophosphorylation in spinach chloroplasts but their effects on the light-triggered ATPase were additive rather than synergistic. The effect was reversed by washing and prevented by dithioerythritol and by cistein. Carbonyl cyanide m-chlorophenylhydrazone (CCP) could replace FCCP but uncouplers of other types like atebrin did not substitute for FCCP.Combinations of FCCP with the four inhibitors synergistically uncoupled ferricyanide reduction in the presence of ADP and Pi but not in their absence. The synergistic uncoupling was not observed on the light-dependent pH rise of chloroplast suspensions.Association of FCCP with any of the inhibitors completely abolished the stimulation of proton uptake or the inhibition of electron transport induced by low concentrations of ATP.This synergistic and peculiar uncoupling can not be ascribed to a modification of membrane permeability. One possible explanation is that the effect requires a conformational state of the membrane-bound coupling factor 1 (CF1) induced by phosphorylating conditions which would facilitate the interaction of inhibitors and FCCP with the membrane. 相似文献
4.
Christoph Giersch Ulrich Heber Yoshichika Kobayashi Yorinao Inoue Kazuo Shibata Hans W. Heldt 《BBA》1980,590(1):59-73
Adenylate concentrations were measured in intact chloroplasts under a variety of conditions. Energy charge was significant in the dark and increased in the light, but remained far below values expected from observed phosphorylation potentials in broken chloroplasts, which were 80 000 M?1 or more in the light. With nitrite as electron acceptor, phosphorylation potentials in intact chloroplasts were about 80 M?1 in the dark and only 300 M?1 in the light. Similar phosphorylation potentials were observed, when oxaloacetate, phosphoglycerate or bicarbonate were used as substrates. ΔG′ATP was ?42 kJ/mol in darkened intact chloroplasts, ?46 kJ/mol in illuminated intact chloroplasts and ?60 kJ/mol in illuminated broken chloroplasts. Uncoupling by NH4Cl, which stimulated electron transport to nitrite or oxaloacetate and decreased the proton gradient, failed to decrease the phosphorylation potential of intact chloroplasts. Also, it did not increase the quantum requirement of CO2 reduction. It is concluded that the proton motive force as conventionally measured and phosphorylation potentials are far from equilibrium in intact chloroplasts. The insensitivity of CO2 reduction and of the phosphorylation potential to a decrease in the proton motive force suggests that intact chloroplasts are over-energized even under low intensity illumination. However, such a conclusion is at variance with available data on the magnitude of the proton motive force. 相似文献
5.
In isolated intact chloroplasts, maximal rates of photosynthetic O2 evolution (in saturating HCO?3) are associated with a critical transthylakoid proton gradient as a result of the stoichiometric consumption of 2 mol NADPH and 3 mol ATP/mol CO2 fixed. Studies with the fluorescent probe 9-aminoacridine reveal that in the illuminated steady state the critical ΔpH is 3.9.CO2-dependent O2 evolution is inhibited by increases of 0.1–0.2 in ΔpH that occur when catalase is omitted from the medium, NO?2 is included as an electron acceptor, or when chloroplasts are illuminated under low partial pressures of O2. Low concentrations of antimycin (0.33 μM) or NH4Cl (0.33 mM) decrease ΔpH and relieve this inhibition of electron flow. The energy transfer inhibitor quercetin lowers the high ATP/ADP ratio associated with these conditions, but does not lower ΔpH or relieve the inhibition.A decrease of ΔpH below 3.9 by weaker illumination, millimolar levels of NH4Cl or micromolar levels of antimycin, results in lower rates of photosynthesis owing to limitation by the phosphorylation rate.These findings show that in absence of rate limitation by the carbon cycle, the extent of thylakoid energization is related to the ratio of ATP to NADPH production and in turn, the rate of CO2 assimilation. 相似文献
6.
J.F. Allen 《FEBS letters》1984,166(2):237-244
Protein phosphorylation in isolated, intact pea chloroplasts was measured during the onset of CO2-dependent O2 evolution. Total incorporation of 32P (from 32Pi) into the light-harvesting chlorophyll a/b—protein was found to be less sensitive than O2 evolution to inhibition by the uncouplers FCCP and NH4C1 It is concluded that changes in the rate of ATP synthesis cannot affect protein phosphorylation without also affecting the rate of CO2-fixation in this system. The ATP/ADP ratio is therefore unlikely to regulate photosynthetic protein phosphorylation under normal physiology conditions. 相似文献
7.
The effects of the tertiary amines tetracaine, brucine and dibucaine on photophosphorylation and control of photosynthetic electron transport in isolated chloroplasts of Spinacia oleracea were investigated. Tertiary amines inhibited photophosphorylation while the related electron transport decreased to the rates, observed under non-phosphorylating conditions. Light induced quenching of 9-aminoacridine fluorescence and uptake of 14C-labelled methylamine in the thylakoid lumen declined in parallel with photophosphorylation, indicating a decline of the transthylakoid proton gradient. In the presence of ionophoric uncouplers such as nigericin, no effect of tertiary amines on electron transport was seen in a range of concentration where photophosphorylation was inhibited. Under the influence of the tertiary amines tested, pH-dependent feed-back control of photosystem II, as indicated by energy-dependent quenching of chlorophyll fluorescence, was unaffected or even increased in a range of concentration where 9-aminoacridine fluorescence quenching and photophosphorylation were inhibited. The data are discussed with respect to a possible involvement of localized proton flow pathways in energy coupling and feed-back control of electron transport.Abbreviations 9-AA
9-aminoacridine
-
J
e
flux of photosynthetic electron transport
- PC
photosynthetic control
- pH1
H+ concentration in the thylakoid lumen
- pmf
proton motive force
- P
potential quantum yield of photochemistry of photosystem II (with open reaction centers)
-
Q
A
primary quinone-type electron acceptor of photosystem II
-
q
Q
photochemical quenching of chlorophyll fluorescence
-
q
E
energy-dependent quenching of chlorophyll fluorescence
-
q
AA
light-induced quenching of 9-amino-acridine fluorescence 相似文献
8.
ATP concentrations were measured in isolated intact spinach chloroplasts under various light and dark conditions. The following results were obtained: (1) Even in darkened chloroplasts and in the absence of exogenous substrates, ATP levels in the chloroplast stroma were significant. They decreased on addition of glycerate, phosphoglycerate or dihydroxyacetone phosphate. When dihydroxyacetone phosphate and oxaloacetate were added together, ATP levels increased in darkened chloroplasts owing to substrate level phosphorylation. (2) Under illumination with saturating single turnover flashes, oxygen evolution in the presence of phosphoglycerate, whose reduction requires ATP, was no lower on a unit flash basis at the low flash frequency of 2 Hz than at higher frequencies. Quenching of 9-aminoacridine fluorescence, which indicates the formation of a proton gradient in intact chloroplasts, decreased with decreasing flash frequencies, until there was no significant fluorescence quenching at a flash frequency of about 2 Hz. In contrast to intact chloroplasts, broken chloroplasts did not phosphorylate much ADP at the low flash frequency of 2 Hz. (3) Flashing at extremely low frequencies (0.2 Hz) caused ATP hydrolysis rather than ATP synthesis in intact chloroplasts. At higher flash frequencies, synthesis replaced hydrolysis. Still, even at high frequencies (10 Hz), the first flashes of a series of flashes given after a long dark time always decreased chloroplast ATP levels. From these results, it is concluded that the enzyme, which mediates ATP synthesis in the light, is inactive in darkened intact chloroplasts. Its light activation can be separated from the formation of the high energy condition, which results in ATP synthesis. After its activation, the enzyme catalyzes a reversible reaction. 相似文献
9.
ATP concentrations were measured in isolated intact spinach chloroplasts under various light and dark conditions. The following results were obtained: (1) Even in darkened chloroplasts and in the absence of exogenous substrates, ATP levels in the chloroplast stroma were significant. They decreased on addition of glycerate, phosphoglycerate or dihydroxyacetone phosphate. When dihydroxyacetone phosphate and oxaloacetate were added together, ATP levels increased in darkened chloroplasts owing to substrate level phosphorylation. (2) Under illumination with saturating single turnover flashes, oxygen evolution in the presence of phosphoglycerate, whose reduction requires ATP, was no lower on a unit flash basis at the low flash frequency of 2 Hz than at higher frequencies. Quenching of 9-aminoacridine fluorescence, which indicates the formation of a proton gradient in intact chloroplasts, decreased with decreasing flash frequencies, until there was no significant fluorescence quenching at a flash frequency of about 2 Hz. In contrast to intact chloroplasts, broken chloroplasts did not phosphorylate much ADP at the low flash frequency of 2 Hz. (3) Flashing at extremely low frequencies (0.2 Hz) caused ATP hydrolysis rather than ATP synthesis in intact chloroplasts. At higher flash frequencies, synthesis replaced hydrolysis. Still, even at high frequencies (10 Hz), the first flashes of a series of flashes given after a long dark time always decreased chloroplast ATP levels.From these results, it is concluded that the enzyme, which mediates ATP synthesis in the light, is inactive in darkened intact chloroplasts. Its light activation can be separated from the formation of the high energy condition, which results in ATP synthesis. After its activation, the enzyme catalyzes a reversible reaction. 相似文献
10.
Photophosphorylation capacity of stable spheroplast preparations of anabaena 总被引:2,自引:2,他引:0
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
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
11.
Effects of heterocyclic and tertiary permeant amines on the electron transfer in thylakoid membranes
The effect of low concentrations (up to 50 μM) of lipophilic permeant amines on the electron transfer in thylakoid membranes
of pea chloroplasts has been investigated. In the presence of heterocyclic amines (9-aminoacridine and neutral red), the electron
transfer, initiated from H2O to PS I acceptors, has been shown to be inhibited to a level amounting to less than 50% of control, this taking place for
both the basal (at alkaline pH) and the gramicidin-uncoupled transport (at pH 6.5–8.5). Under the same conditions, tertiary
amines (dibucaine, tetracaine) cause only a 10–15% inhibition of transport. With all the amines, the rate of electron transport
from H2O to DCBQ, PS II acceptor is decreased to 80–90% of control at pH above 8.0, but this effect is completely removed when pH
is lowered to 7.7–6.5. In the region of PS I, all the amines accelerate the basal transport, but do not influence the uncoupled
electron transfer. A conclusion has been drawn that, parallel with uncoupling, heterocyclic and tertiary amines also cause
an inhibition of PS II, appearing at alkaline pH values. Additionally, heterocyclic amines seem to brake electron flow at
the level of plastoquinone reduction.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
12.
Adenylate levels in chloroplasts, mitochondria and the cytosol of oat mesophyll protoplasts were determined under light and dark conditions, in the absence and presence of plasmalemma-permeable inhibitors of electron transfer and uncouplers of phosphorylation. This was achieved using a microgradient technique which allowed an integrated homogenization and fractionation of protoplasts within 60 s (Hampp et al. 1982, Plant Physiol. 69, 448–455), under conditions which quench bulk activities of metabolic interconversion in less than 2 s. In illuminated controls, ATP/ADP ratios were found to be 2.1 in chloroplasts, about unity in mitochondria, and 11 in the cytosol; whereas, in the dark, this ratio only showed a large drop in chloroplasts (0.4). None of the compounds used [carbonylcyanide m-chlorophenylhydrazone (CCCP), carbonylcyanide p-trifluoromethoxy-phenylhydrazone (FCCP), antimycin A, dibromothymoquinone (DBMIB), dichlorophenyldi-methylurea (DCMU), or salicylhydroxamic acid (SHAM)] affected the stroma adenylate ratio in the dark. Under illumination, however, the ATP/ADP ratios were partly reduced in the presence of antimycin (inhibitor of cyclic photophosphorylation) and of DCMU (inhibitor of linear electron flow), while in the presence of DBMIB, DCMU+ antimycin (inhibition of both cyclic and linear electron flow), and CCCP (uncoupling) the ratio obtained was the same as that occurring in the dark. In contrast, mitochondrial adenylate levels did not exhibit large variations under the various treatments. The cytosolic ATP/ADP ratio, however, showed dramatic changes: in darkened protoplasts, cytosolic values dropped to 0.2 and 0.1 in the presence of uncouplers and antimycin, respectively, while SHAM did not induce any significant alteration. In the light, a similar pronounced decrease in ATP levels was observed only after the application of uncouplers or inhibitors of both mitochondrial and photosynthetic electron transport, whereas selective inhibition of the latter was largely ineffective in reducing the cytosolic ATP/ADP ratio. Thus, the results show that the antimycin-sensitive electron transport is, potentially, equally active in light and darkness. In addition, they indicate that antimycin-insensitive electron transport in mitochondria (alternative pathway) does not significantly contribute to the cytosolic energy state.Abbreviations CCCP
carbonylcyanide m-chlorophenylhydrazone
- DBMIB
dibromothymoquinone (2,5-dibromo-3-methyl-6-isopropy-p-benzoquinone)
- DCMU
dichlorophenyldimethylurea
- FCCP
carbonylcyanide-p-trifluoromethoxy-phenylhydrazone
- SHAM
sancylhydroxamic acid 相似文献
13.
1. The inhibitory action of tetraphenylboron, a lipid-soluble anion, on the proton uptake, the photophosphorylation and the light-induced quenching of the fluorescence of 9-aminoacridine by spinach chloroplasts was studied.2. The inhibition of the three processes by tetraphenylboron was transient; the proton uptake was affected to a much smaller extent than either the photophosphorylation or the fluorescence quenching.3. The inhibitory effects of tetraphenylboron on the proton uptake and the fluorescence quenching of 9-aminoacridine were qualitatively the same in CF1-depleted chloroplasts, that were recoupled with N,N′-dicyclohexylcarbodiimide (DCCD).4. The reversal of the fluorescence quenching of 9-aminoacridine upon addition of tetraphenylboron in the light was found to be very fast, being completed within the response time of the apparatus.5. The presence of tetraalkylammonium salts in the incubation medium prevented the inhibitory effect of tetraphenylboron.6. Tetraphenylboron disappeared from the chloroplast suspension in a light-dependent irreversible way; in the dark no ‘ptake’ of tetraphenylboron could be detected.7. The effects of tetraphenylboron may be explained by the presence of groups with a high affinity for tetraphenylboron in the membrane; these groups become protonated upon illumination of the chloroplasts. 相似文献
14.
Lars-Göran Sundblad Göran Samuelsson Bosse Wigge Per Gardeström 《Photosynthesis research》1990,23(3):269-282
Two green algal species, Chlamydomonas reinhardtii and Scenedesmus obliquus, exhibited a relative maximum during the decay of luminescence, when adapted to low CO2 conditions that was not observed in high CO2 adapted cells.From the kinetics of transient changes in the level of dark fluorescence, after illumination and parallel to the luminescence maxima, it was concluded that the maximum in Scenedesmus was mainly related to a decrease in nonphotochemical quenching, whereas in Chlamydomonas the maximum was mainly related to a dark reduction of the primary PS II acceptor QA.ATP/ADP ratios from low CO2 adapted Scenedesmus showed transient high levels after a dark/light transition that was not observed in high CO2 adapted cells. After 30 s of illumination the ATP/ADP ratios however stabilized at the same steady state level as in high CO2 adapted cells.Dark addition of HCO3
- to low CO2 adapted cells of Chlamydomonas resulted in a rapid transient quenching of luminescence that was not observed in low CO2 adapted cells of neither species.It is concluded that the luminescence maxima present in both low CO2 adapted Scenedesmus and Chlamydomonas reflect adaptation of the cells to low CO2 conditions. It is further suggested that the difference in mechanistic origin of luminescence maxima in the two species reflects differences in adaptation.Abbreviations ADP
adenosine-diphosphate
- ATP
adenosine-triphosphate
- Ci
inorganic carbon
- FD
dark fluorescence recorded under dark adapted conditions
- F0
fluorescence with all reaction centers open
- FV
variable fluorescence
- PS I
photosystem I
- PS II
photosystem II
- QA
the first quinone acceptor of PS II 相似文献
15.
Energetic factors affecting carbon dioxide fixation in isolated chloroplasts 总被引:3,自引:3,他引:0
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Light- and HCO3−-saturated (10 millimolar) rates of O2 evolution (120 to 220 micromoles O2 per milligram chlorophyll per hour), obtained with intact spinach chloroplasts, are decreased up to 3-fold by changes in assay conditions such as omission of catalase from the medium, the use of high (≥1 millimolar) inorganic phosphate, inclusion of NO2− as an electron acceptor, or bright illumination at low partial pressures of O2. These inhibitions may be reversed by addition of uncoupling levels of NH4Cl or of antimycin concentrations that partially block cyclic electron transfer between cytochrome b6 and cytochrome f. Measurements of the pH gradient across the thylakoid membrane with the fluorescent probe, 9-aminoacridine, indicate that changes in ΔpH are sufficient to account for both the inhibited and restored rates of electron transport. It follows that the rate of HCO3−-saturated photosynthesis may be restricted by a proton gradient back pressure under these conditions. 相似文献
16.
G. H. Krause 《Planta》1978,138(1):73-78
Uncoupling concentrations (about 1 mol l-1) of desaspidin or carbonyl cyanide-4-trifluoromethoxyphenyl hydrazone reverse the slow light-induced, Mg2+-dependent quenching of fluorescence of chlorophyll a in isolated (intact and broken) spinach chloroplasts. Likewise, uncoupling inhibits the light-induced increase of the Mg2+ concentration in the stroma of intact chloroplasts, as determined with Eriochrome Blue SE. Addition of higher amounts of the uncouplers to the chloroplasts leads to a slow, light-dependent fluorescence lowering which appears to be promoted by high light intensities and is not reversed in the dark. The reversal of the fluorescence quenching by uncoupling is interpreted to reflect exchange of protons for Mg2+ ions at negative sites of the inner thylakoid face, caused by the collapse of the proton gradient across the membrane. The secondary fluorescence lowering caused by high levels of the uncouplers and high light intensities is suggested to be related to an inhibition of non-cyclic photosynthetic electron transport.Abbreviation FCCP
carbonyl cyanide-4-trifluoromethoxyphenyl hydrazone 相似文献
17.
In the absence of electron acceptors and of oxygen a proton gradient was supported across thylakoid membranes of intact spinach chloroplasts by far-red illumination. It was decreased by red light. Inhibition by red light indicates effective control of cyclic electron flow by Photosystem II. Inhibition was released by oxygen which supported a large proton gradient. Oxygen appeared to act as electron acceptor simultaneously preventing over-reduction of electron carriers of the cyclic electron transport pathway. It thus has an important regulatory function in electron transport. Under anaerobic conditions, the inhibition of electron transport caused by red illumination could also be released and a large proton gradient could be established by oxaloacetate, nitrite and 3-phosphoglycerate, but not by bicarbonate. In the absence of oxygen, ATP levels remained low in chloroplasts illuminated with red light even when bicarbonate was present. They increased when electron acceptors were added which could release the over-reduction of the electron transport chain. Inhibition of electron transport in the presence of bicarbonate was relieved and CO2-fixation was initiated by oxygen concentrations as low as about 10 μM. Once CO2 fixation was initiated, very low oxygen levels were sufficient to sustain it. The results support the assumption that pseudocyclic electron transport is necessary to poise the electron transport chain so that a proper balance of linear and cyclic electron transport is established to supply ATP for CO2 reduction. 相似文献
18.
(1) The relation between the membrane potential and phosphorylation was studied in chloroplasts rapidly prepared from illuminated spinach leaves (light chloroplasts) and from dark-adapted leaves (dark chloroplasts). Light chloroplasts had a higher ATP hydrolysis activity than dark chloroplasts. (2) In the presence of ADP or ATP, a rapidly decaying phase of the field-indicating 518 nm absorbance change with a half-time of 15 ms became apparent in addition to the slow phase with a half-time of more than 300 ms in either type of chloroplast. Under these conditions, light chloroplasts showed a larger rapid phase than dark chloroplasts. (3) The rapid phase was suppressed by dicyclohexylcarbodiimide and was assumed to reflect the dissipation of membrane potential due to proton movements inside the CF1-CF0 ATP synthetase. (4) A model for the proton movement in ATP synthetase is proposed. 相似文献
19.
《FEBS letters》1987,212(1):114-118
Barley (Hordeum vulgare) protoplasts were incubated in darkness and in the light at saturating and limiting CO2 concentrations. The protoplasts were fractioned by a membrane filtration technique which allows quenching of the metabolism by acidification within about 0.1 s and the ATP/ADP ratios in the cytasol, chloroplasts and mitochondria were determined. It is concluded that the cytosolic ATP/ADP ratio is considerably higher during photosynthesis at limiting CO2 (which is the normal situation for a C3 plant in air) compared to photosynthesis at saturating CO2 or darkness. 相似文献
20.
McCarty RE 《Journal of bioenergetics and biomembranes》2006,38(1):67-74
Oxidized ATP synthase of spinach thylakoid membranes catalyzes high rates of ATP synthesis in the light, but very low rates of ATP hydrolysis in the dark. Reduction of the disulfide bond in the γ subunit of the ATP synthase in the light enhances the rate of Mg2+-ATP hydrolysis in the dark. The light plus thiol-activated state decays in a few minutes in the dark after illumination in Tris buffer, but not when Tricine was used in place of Tris. In this paper, it is shown that Tris in the assay mixture is an inhibitor of the light plus thiol-activated ATPase activity of thylakoids, but only after the activated membranes had incubated in the dark. Aminopropanediols and diethanolamine, also selectively inhibited ATPase activity of activated membranes after storage in the dark, whereas NH4Cl and imidazole inhibit the ATPase activity of activated thylakoids almost equally whether they are added directly after the illumination or several minutes later. The fluorescence of 9-amino-6-chloro-2-methoxyacridine (ACMA) is quenched by the establishment of proton gradients by ATP-dependent proton uptake. Addition of ATP to activated membranes results in rapid quenching of ACMA fluorescence. If the activated membranes were incubated in the dark prior to ATP addition, a lag in the ATP-dependent ACMA fluorescence quenching as well as a similar lag in the rate ATP hydrolysis were seen. It is concluded that ADP rebinds to CF1 in the dark following illumination and inhibits the activity of the ATP synthase. Reactivation of the ATP synthase in the dark can occur by the slow generation of proton gradients by ATP hydrolysis in the dark. This reactivation takes place in Tricine buffer, but not in Tris because of its uncoupling action. Whether ADP binding plays a role in the regulation of the activity of the ATP synthase in situ remains to be established. 相似文献