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1.
1. Dihydroxyacetone phosphate in concentrations greater than or equal to 2.5 mM completely inhibits CO2-dependent O2 evolution in isolated intact spinach chloroplasts. This inhibition is reversed by the addition of equimolar concentrations of Pi, but not by addition of 3-phosphoglycerate. In the absence of Pi, 3-phosphoglycerate and dihydroxyacetone phosphate, only about 20% of the 14C-labelled intermediates are found in the supernatant, whereas in the presence of each of these substances the percentage of labelled intermediates in the supernatant is increased up to 70-95%. Based on these results the mechanism of the inhibition of O2 evolution by dihydroxyacetone phosphate is discussed with respect to the function of the known phosphate translocator in the envelope of intact chloroplasts. 2. Although O2 evolution is completely suppressed by dihydroxyacetone phosphate, CO2 fixation takes place in air with rates of up to 65 mu mol-mg1 chlorophyll-h1. As non-cyclic electron transport apparently does not occur under these conditions, these rates must be due to endogenous pseudocyclic and/or cyclic photophosphorylation. 3. Under anaerobic conditions, the rates of CO2 fixation in presence of dihydroxyacetone phosphate are low (2.5-7 mumol-mg1 chlorophyll-h1), but they are strongly stimulated by addition of dichlorophenyl-dimethylurea (e.g. 2-10(-7) M) reaching values of up to 60 mumol-mg1 chlorophyll-h1. As under these conditions the ATP necessary for CO2 fixation can be formed by an endogenous cyclic photophosphorylation, the capacity of this process seems to be relatively high, so it might contribute significantly to the energy supply of the chloroplast. As dichlorophenyl-dimethylurea stimulates CO2 fixation in presence of dihydroxyacetone phosphate under anaerobic but not under aerobic conditions, it is concluded t-at only under anaerobic conditions an "overreduction" of the cyclic electron transport system takes place, which is removed by dichlorophenyl-dimethylurea in suitable concentrations. At concentrations above 5-10(-7) M dichlorophenyl-dimethylurea inhibits dihydroxyacetone phosphate-dependent CO2 fixation under anaerobic as well as under aerobic conditions in a similar way as normal CO2 fixation. Therefore, we assume that a properly poised redox state of the electron transport chain is necessary for an optimal occurrence of endogenous cyclic photophosphorylation. 4. The inhibition of dichlorophenyl-dimethylurea-stimulated CO2 fixation in presence of dihydroxyacetone phoshate by dibromothymoquinone under anaerobic conditions indicated that plastoquinone is an indispensible component of the endogenous cyclic electron pathway.  相似文献   

2.
When intact chloroplasts are incubated in the dark with dihydroxyacetone phosphate, an increase in fructose 1,6-bisphosphatase activity occurs which resembles the reductive activation observed in illuminated chloroplasts. Under optimum conditions, the activity increases to about 150 μmol · h?1 · mg?1 chlorophyll within 60 min. The dark activation of the enzyme is reversed by electron acceptors such as oxaloacetate, nitrite, and 3-phosphoglycerate plus ATP. Activation is most marked under strictly anaerobic conditions, being strongly inhibited by O2. It is concluded that NADPH, generated from dihydroxyacetone phosphate in situ in the reaction catalyzed by NADP+-dependent glyceraldehyde phosphate dehydrogenase, can provide electrons for the reductive activation of fructose 1,6-bisphosphatase in the dark.  相似文献   

3.
This study examines the capacity of intact spinach (Spinacia oleracea L.) chloroplasts to fix 14CO2 when supplied with Benson-Calvin cycle intermediates in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). Under these conditions, substantial 14CO2 fixation occurred in the light but not in the dark when either dihydroxyacetone phosphate, ribulose 5-phosphate, fructose 6-phosphate, or fructose bisphosphate was added. The highest rate of 14CO2 fixation (20-40 micromoles per milligram chlorophyll per hour) was obtained with dihydroxyacetone phosphate. In contrast, no 14CO2 fixation occurred when 3-phosphoglycerate was used. 14CO2 fixation in the presence of dihydroxyacetone phosphate and DCMU was inhibited by carbonylcyanide m-chlorophenylhydrazone, dl-glyceraldehyde, and pyridoxal 5′-phosphate. Low concentrations of O2 (25-50 micromolar) stimulated 14CO2 fixation, but the activity decreased with increasing O2 concentrations. The fixation of 14CO2 in the presence of DCMU and dihydroxyacetone phosphate was also observed in maize bundle sheath cells. These results provide direct evidence for cyclic photophosphorylation in intact chloroplasts. The activity measured is adequate to support all the extra ATP requirements for maximum rates of photosynthesis in these intact chloroplasts.  相似文献   

4.
Mizuho Komatsu  Satoru Murakami 《BBA》1976,423(1):103-110
ATP and pyrophosphate at high concentration (> 1 mM) inhibited photophosphorylation of isolated spinach chloroplasts in the normal salt medium and did not cause stimulation of electron transport. The inhibition of photophosphorylation by ATP or pyrophosphate was shown to be abolished by the addition of excess MgCl2, ADP and phosphate. It has been demonstrated that the rates of photophosphorylation in the absence and presence of ATP or pyrophosphate are determined similarly by the concentrations of magnesium-ADP (Mg · ADP?) and magnesium-phosphate (Mg · Pi) complexes.It is highly probable that Mg · ADP? and Mg · Pi, but not free ADP and free phosphate, are the active form of the substrates of photophosphorylation. This is in support of the view that ATP inhibits photophosphorylation by decreasing the concentration of Mg2+ which is available for the formation of the complex with ADP and phosphate.  相似文献   

5.
Teruo Ogawa 《BBA》1982,681(1):103-109
Illumination of leaves of Vicia faba L. provoked oscillations in the rates of CO2 uptake and O2 evolution. The oscillations were marked under anaerobic conditions, but were absent at 20% O2. The minimum CO2 concentration required for the appearance of oscillations was 600 μl · l?1. The higher the CO2 concentration, the stronger the oscillations. The effect of CO2 concentration was saturated at 1000 μl CO2 · l?1. The period of the oscillations was 5–6 min at a light intensity of 80 nE · cm?2 · s?1 and became longer on lowering of the intensity. No oscillations appeared at intensities below 12 nE · cm?2 · s?1. Oscillations could also be generated by increasing the CO2 concentration in the atmosphere during strong illumination under anaerobic conditions. The chlorophyl a fluorescence yield showed oscillations, similar in shape and frequency to those of photosynthesis, after such an environmental change. Oscillations were also observed in photosynthesis of other C3 plants, Lycopersicon esulentum Mill and Glycine max Merrill, under the same conditions as those required for V. faba, but were absent for the C4 plants, Zea mays and Amaranthus retroflexus L.  相似文献   

6.
Under anaerobic conditions in the light, active K influx inHydrodictyon africanum is supported by cyclic photophosphorylation.The use of selective inhibitors shows that, in the presenceof CO2, a considerable portion of the ATP used by the K pumpis supplied by noncyclic photophosphorylation. The rest of theATP in these conditions comes from cyclic photophosphorylation.This is true under light-limiting as well as light-saturatedconditions. If non-cyclic photophosphorylation is inhibited (by removalof carbon dioxide, by the addition of cyanide which interfereswith the carboxylation reaction, or by inhibition of photosystemtwo with DCMU or supplying only far-red light), the K influxat low light intensities is stimulated, and its characteristicsbecome those of a process powered by cyclic photophosphorylationalone. These results are interpreted in terms of a competitionfor ATP between K influx and CO2 fixation. Implicit in thisexplanation is a requirement for a switch of excitation energyabsorbed by photosystem one from cyclic photophosphorylationto non-cyclic photophosphorylation whenever conditions (presenceof CO2and photosystem two activity) allow CO2 fixation to occur. Further evidence for such a switch of excitation energy absorbedby photosystem one was obtained in experiments in which redand far-red light were applied separately and together. It wasfound that CO2 fixation showed the Emerson enhancement effect,while K influx (in the presence of CO2) shows a ‘de-enhancement’.This suggests that far-red light alone powers cyclic photophosphorylation;if red light is also present, some of the far-red quanta arediverted to non-cyclic photophosphorylation. The nature of the interaction between cyclic and non-cyclicphotophosphorylation is discussed in relation to these and otherpublished results.  相似文献   

7.
1. The pH in the stroma and in the thylakoid space has been measured in a number of chloroplast preparations in the dark and in the light at 20 °C. Illumination causes a decrease of the pH in the thylakoid space by 1.5 and an increase of the pH in the stroma by almost 1 pH unit.2. CO2 fixation is shown to be strongly dependent on the pH in the stroma. The pH optimum was 8.1, with almost zero activity below pH 7.3. Phosphoglycerate reduction, which is a partial reaction of CO2 fixation, shows very little pH dependency.3. Low concentrations of the uncoupler m-chlorocarbonylcyanide phenylhydrazone (CCCP) inhibit CO2 fixation without affecting phosophoglycerate reduction. This inhibition of CO2 fixation appears to be caused by reversal of light induced alkalisation in the stroma by CCCP.4. Methylamine has a very different effect compared to CCCP. Increasing concentrations of methylamine inhibit CO2 fixation and phosphoglycerate reduction to the same extent. The light induced alkalisation of the stroma appears not to be significantly inhibited by methylamine, but the protons in the thylakoid space are neutralized. The inhibition of CO2 fixation by higher concentrations of methylamine is explained by an inhibition of photophosphorylation. It appears that methylamine does not abolish proton transport.5. It is shown that intact chloroplasts are able to fix CO2 in the dark, yielding 3-phosphoglycerate. This requires the addition of dihydroxyacetone phosphate as precursor of ribulosemonophosphate and also to supply ATP, and the addition of oxaloacetate for reoxidation of the NADPH in the stroma.6. Dark CO2 fixation in the presence of dihydroxyacetone phosphate and oxaloacetate has the same pH dependency as CO2 fixation in the light. This demonstrates that CO2 fixation in the dark is not possible, unless the pH in the medium is artificially raised to pH 8.8.7. It is shown that pH changes occurring in the stroma after illumination are sufficient to switch CO2 fixation from zero to maximal activity. This offers a mechanism for light control of CO2 fixation, avoiding wasteful CO2 fixation in the dark.  相似文献   

8.
The role of cyclic photophosphorylation in vivo   总被引:1,自引:0,他引:1       下载免费PDF全文
When cyclic photophosphorylation is inhibited in Chlorella vulgaris cells by carbonylcyanide-trifluoromethoxy phenylhy-drazone, photosynthetic CO2-fixation under anaerobic conditions exhibits a distinct lag. Under the same conditions, the light-dependent formation of ribulose diphosphate shows also this lag. It is concluded that cyclic photophosphorylation is required to fill up the pools of phosphorylated intermediates of the Calvin cycle at a time when noncyclic photophosphorylation cannot yet efficiently operate. Under aerobic conditions, the initial energy demand can be accommodated by respiratory ATP or cyclic photophosphorylation or both. Evidence for stoichiometric participation of cyclic photophosphorylation in photosynthesis is still lacking.  相似文献   

9.
Rates of photosynthesis by the marine macroalga Ulva lactuca were measured in a factorial experiment at five concentrations of HCO3? and CO32- between 0·20 and 1·26 mol m?3, but very low concentrations of CO2. The results demonstrated that HCO3? was available for use, but an analysis of variance showed that CO32- had neither an inhibiting nor a stimulating effect on rates of photosynthesis over this concentration range. Over the experiment, pH varied from 8·46 to 10·06 and this also had no significant effect on rates of photosynthesis. The lack of a stimulatory effect of high concentrations of CO32- on the rate of photosynthesis at low concentrations of HCO3? was taken as circumstantial evidence for direct uptake of HCO3? rather than proton extrusion and external production of CO2. In the rockpools in which U. lactuca grows, pH values up to 10·35 have been recorded, and for much of the time, CO32- was the major form of inorganic carbon available. The apparent lack of an ability to use CO32- under these conditions suggests that direct use of CO32- as a source of inorganic carbon for photosynthesis is unlikely to be widespread.  相似文献   

10.
The relation between light-induced electron transport with NO3?, NO2? or CO2 as acceptors, ATP pools and transients in dark-light-dark transitions, and phosphate uptake was examined in phosphorus-starved cells of Scenedesmus obtusiusculus Chod. Net O2 evolution at saturating light was around 6 μmol × (mg chlorophyll × h)?1 in the absence of any acceptor, but reached average rates of 21, 65 and 145 μmol × (mg chlorophyll × h)?1 upon additions of 5 mM KNO3, KNO2 and KHCO3, respectively. The apparent rate of photophosphorylation in transition experiments was only a few percent of the rate calculated from CO2-dependent O2 evolution. Blocking non-cyclic electron transport with DCMU inhibited phosphate assimilation, but acceleration of non-cyclic electron flow by addition of NO3? or NO2? did not stimulate phosphate assimilation as compared to the situation without an acceptor. A functional non-cyclic system might primarily be needed for an efficient shuttle transfer of ATP from the chloroplast to the cytoplasm. An inhibition of the non-cyclic system due to lack of reducible substrates accelerates the cyclic system and thus indicates a regulation mechanism between the two systems.  相似文献   

11.
Salicylaldoxime (2 × 10−3m and less) inhibits cyclic photophosphorylation in intact Chlorella cells severely whereas photosynthetic O2-evolution and 14CO2-fixation is hardly affected. Cyclic photophosphorylation in vivo was measured by following anaerobic light dependent glucose uptake. A similar difference in susceptibility has been observed with carbonylcyanide-p-trifluoromethoxyphenylhydrazone. Various controls exclude the possibility that the difference in inhibition was caused by differing experimental conditions or, in the case of glucose assimilation, by an inhibition of a reaction other than photophosphorylation.  相似文献   

12.
M. R. Kirk  U. Heber 《Planta》1976,132(2):131-141
Summary Intact chloroplasts capable of high rates of CO2 assimilation completely oxidized 3-phosphoglycerate and dihydroxyacetone phosphate to glycolate when CO2 concentrations were low. Bicarbonate was converted first into products of the Calvin cycle and then into glycolate. Under high oxygen and at high pH values CO2 fixation and glycolate formation ceased before bicarbonate was exhausted. This is interpreted as the consequence of a depletion of ribulose diphosphate (RuDP) at the oxygen compensation point, where oxygen consumption by glycolate formation and oxygen evolution by phosphoglycerate reduction balance each other. Depletion of RuDP by glycolate formation is proposed to play a role in the Warburg effect. The maximum rate of glycolate synthesis observed with dihydroxyacetone phosphate as substrate was 35 mol mg-1 chlorophyll h-1 at 20°C. This may not reflect the maximum capacity of chloroplasts for glycolate synthesis. Dithiothreitol and catalase, which prevent accumulation of oxygen radicals or H2O2 during carbon assimilation, increased glycolate formation. H2O2 was inhibitory. Other inhibitors of glycolate formation were glyceraldehyde and carbonylcyanide p-trifluoro-methoxphenylhydrazone. From the sensitivity of glycolate synthesis to uncoupling and the ATP requirement of RuDP formation it is concluded that glycolate originated from RuDP. Different induction periods of carbon fixation and glycolyte formation suggested that glycolate synthesis is not only regulated by the ratio of oxygen to CO2 but also by another factor.  相似文献   

13.
The photosynthetic capacity of submerged Ulva sp. when utilizing CO2 and HCO?3 as exogenous carbon forms has been investigated and compared with ambient carbon concentrations in sea water. Saturating concentrations of HCO? 3 and CO2 were 1200 and 100 μM, respectively at saturating light, and photosynthetic rates under such conditions averaged 700 μmolO2·gDW?1 ·h?1. The HCO?3 concentration of sea water (≈2500μM), was thus found to be saturating for photosynthesis of Ulva. At the CO2 concentration of sea water (≈ 10 μM), the contribution of this carbon form to photosynthesis could be 27% at the most. Under conditions of slow water movement, the relative importance of CO2 utilization would probably be minimized in favour of HCO?3 utilization. It is concluded that HCO?3 uptake is not limiting photosynthesis for Ulva under natural conditions.  相似文献   

14.
S.G. Reeves  D.O. Hall 《BBA》1973,314(1):66-78
1. The stoichiometry of non-cyclic photophosphorylation and electron transport in isolated chloroplasts has been re-investigated. Variations in the isolation and assay techniques were studied in detail in order to obtain optimum conditions necessary for reproducibly higher ADP/O (equivalent to ATP/2e?) and photosynthetic control ratios.2. Studies which we carried out on the possible contribution of cyclic phosphorylation to non-cyclic phosphorylation suggested that not more than 10% of the total phosphorylation found could be due to cyclic phosphorylation.3. Photosynthetic control, and the uncoupling of electron transport in the presence of NH4Cl, were demonstrated using oxidised diaminodurene as the electron acceptor. A halving of the ADP/O ratio was found, suggesting that electrons were being accepted between two sites of energy conservation, one of which is associated with Photosystem I and the other associated with Photosystem II.4. ATP was shown to inhibit State 2 and State 3 of electron transport, but not State 4 electron transport or the overall ADP/O ratio, thus confirming its activity as an energy transfer inhibitor. It is suggested that part of the non-phosphorylating electron transport rate (State 2) which is not inhibited by ATP is incapable of being coupled to subsequent phosphorylation triggered by the addition of ADP (State 3). If the ATP-insensitive State 2 electron transport is deducted from the State 3 electron transport when calculating the ADP/O ratio, a value of 2.0 is obtained.5. The experiments reported demonstrate that there are two sites of energy conservation in the non-cyclic electron transfer pathway: one associated with Photosystem II and the other with Photosystem I. Thus, non-cyclic photophosphorylation can probably produce sufficient ATP and NADPH “in vivo” to allow CO2 fixation to proceed.  相似文献   

15.
The carboxylase activities of crude carboxysome preparations obtained from the wild-type Synechococcus elongatus strain PCC 7942 strain and the mutant defective in the carboxysomal carbonic anhydrase (CA) were compared. The carboxylation reaction required high concentrations of bicarbonate and was not even saturated at 50 mM bicarbonate. With the initial concentrations of 50 mM and 25 mM for bicarbonate and ribulose-1,5-bisphosphate (RuBP), respectively, the initial rate of RuBP carboxylation by the mutant carboxysome (0.22 μmol mg?1 protein min?1) was only 30 % of that observed for the wild-type carboxysomes (0.71 μmol mg?1 protein min?1), indicating the importance of the presence of CA in efficient catalysis by ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). While the mutant defective in the ccmLMNO genes, which lacks the carboxysome structure, could grow under aeration with 2 % (v/v) CO2 in air, the mutant defective in ccaA as well as ccmLMNO required 5 % (v/v) CO2 for growth, indicating that the cytoplasmically localized CcaA helped utilization of CO2 by the cytoplasmically localized Rubisco by counteracting the action of the CO2 hydration mechanism. The results predict that overexpression of Rubisco would hardly enhance CO2 fixation by the cyanobacterium at CO2 levels lower than 5 %, unless Rubisco is properly organized into carboxysomes.  相似文献   

16.
Particulate fractions (10,000g) from pupae of Stomoxys calcitrans transfer [14C]-mannose from GDP-[14C]-mannose to dolichol monophosphate and proteins. Production of the mannosyl lipid was inhibited by Mn2+, UDP, GMP, GDP, and EDTA. The insect growth regulator diflubenzuron had no effect on mannosyl transferase activity. Dolichol monophosphate and Mg2+ stimulated mannosyl transferase activity. The mannosyl lipid product was identified as mannosyl-phosphoryl-dolichol (Man-P-Dol). The apparent Km and Vmax values for the formation of Man-P-Dol using GDP-[14C]-Man while holding dolichol phosphate constant were 2.4 ± 0.9 μM and 9.4 ± 2.3 pmol Man-P-Dol·min?1·mg?1 protein, respectively. The apparent Km and Vmax values using dólichol phosphate while holding GDP-Man constant were 2.2 ± 1.2 μM and 18.5 ± 1.7 pmol Man-P-Dol·min?1·mg?1 protein.  相似文献   

17.
《BBA》1986,848(3):392-401
Spinach leaves were illuminated at various temperatures or CO2 concentrations until steady-state photosynthesis could be measured. Subsequently, they were frozen rapidly in liquid nitrogen and freeze-dried. From the dry material, chloroplasts were isolated in a mixture of organic solvents in which polar metabolites are insoluble. Metabolite levels were determined in the chloroplast fraction. From measured levels of dihydroxyacetone phosphate, fructose 6-phosphate (Fru-6-P), ribulose 1,5-bisphosphate (Rbu-1,5-P2), ATP and ADP, mass-action ratios of the reaction dihydroxyacetone phosphate + 2 glyceraldehyde 3-phosphate + 3 ATP + Fru-6-P → 3 Rbu-1,5-P2 + 3 ADP + Pi were computed. They increased at constant light intensity with increasing CO2 concentration or increasing temperature as photosynthetic flux increased. Surprisingly, however, mass action ratios decreased as flux increased with increasing light intensities. Moreover, mass-action ratios were linearly correlated to light-limitation coefficients which were obtained by computing the light limitation of photosynthesis from the slopes of light and CO2 response curves and multiplying obtained values with that increment of photosynthesis which was measured on increasing the light intensity to saturation. The results are interpreted to indicate tight enzymic control of the formation of ribulose bisphosphate by light. As light intensities are increased, light-regulated enzymes are activated to an extent which permits a decrease in the mass action ratios instead of the increase expected to drive increased carbon flux. Since the reactions catalyzed by phosphoglycerate kinase, glyceraldehyde-3-phosphate dehydrogenase and triosephosphate isomerase are close to thermodynamic equilibrium even when photosynthetic fluxes are large, ratios of dihydroxyacetone phosphate to 3-phosphoglycerate indicated the state of chloroplast phosphorylation potentials and the redox state of NADP which together form the assimilatory power [ATP] · [ADP]−1 · [Pi]−1 · [NADPH] · [NADP+]−1. Assimilatory power decreased as carbon flux increased with increasing light intensity and increasing CO2 concentration, but increased as carbon flux increased with increasing temperature. Again this indicates a decrease in the flow resistance of the carbon cycle as light or CO2 is increased. The decrease in the flow resistance is attributed to enzyme activation when light is increased, or to increased carboxylation when CO2 is increased.  相似文献   

18.
Narrow concentration intervals were used, covering 10?6– 10?4M desaspidin. The interaction with glycolysis involves three steps, the inhibitor constants (Ki:s) being in turn 2.7 × 10?5M, 1.3 × 10?4M, and high. About 18% of total glycolysis is inhibited in each of the two first steps, and 65% left for the third reaction. After compensation for glycolysis, oxidative phosphorylation may show a sudden jump to about 10% inhibition at 1.5 × 10?5M desaspidin, the possible Ki of the reaction starting here being very high. Correcting for glycolysis, desaspidin affects total Photophosphorylation in two steps, with the Ki values of 7.8 × 10?5M and 4.6 × 10?4M respectively. Inhibition in the first step is about 27% of the total photophosphorylation. By applying 10?6M DCMU[/3-(3, 4-dichlorophenyl)-l, l-dimethy lurea], one can abolish non-cyclic photophosphorylation. Desaspidin then reacts in a single step with a Ki of 1.4 × 10?4M. At 5 × 10?5M DCMU, also the pseudocyclic photophosphorylation is abolished. The remaining, true cyclic photophosphorylation has a single Ki of 2.3 × 10?5M for desaspidin. Under non-cyclic conditions, the true cyclic process contributes about 25% to total Photophosphorylation. Under pseudocyclic conditions, no cyclic photophosphorylation occurs. Under true cyclic conditions, the non-cyclic and pseudocyclic processes are inoperative. This indicates a regulative system, so that either (1) the (non-cyclic + true cyclic), (2) only the pseudocyclic, or (3) only the true cyclic systems can be traced, dependent on the level of DCMU applied. There are two sites for non-cyclic Photophosphorylation, one of them common to the pseudocyclic pathway. Cyclic photophosphorylation has a third site, different from the other two.  相似文献   

19.
Adult zebrafish Danio rerio were exposed to an electric shock of 3 V and 1A for 5 s delivered by field backpack electrofishing gear, to induce a taxis followed by a narcosis. The effect of such electric shock was investigated on both the individual performances (swimming capacities and costs of transport) and at cellular and mitochondrial levels (oxygen consumption and oxidative balance). The observed survival rate was very high (96·8%) independent of swimming speed (up to 10 body length s?1). The results showed no effect of the treatment on the metabolism and cost of transport of the fish. Nor did the electroshock trigger any changes on muscular oxidative balance and bioenergetics even if red muscle fibres were more oxidative than white muscle. Phosphorylating respiration rates rose between (mean 1 s.e. ) 11·16 ± 1·36 pmol O2 s?1 mg?1 and 15·63 ± 1·60 pmol O2 s?1 mg?1 for red muscle fibres whereas phosphorylating respiration rates only reached 8·73 ± 1·27 pmol O2 s?1 mg?1 in white muscle. Such an absence of detectable physiological consequences after electro‐induced narcosis both at organismal and cellular scales indicate that this capture method has no apparent negative post‐shock performance under the conditions of this study.  相似文献   

20.
J. Michael Gould 《BBA》1975,387(1):135-148
1. The Photosystem I-mediated transfer of electrons from diaminodurene, diaminotoluene and reduced 2,6-dichlorophenolindophenol to methylviologen is optimal at pH 8–8.5, where phosphorylation is also maximal. In the presence of superoxide dismutase, the efficiency of phosphorylation rises from ? 0.1 at pH 6.5 to 0.6–0.7 at pH 8–8.5, regardless of the exogenous electron donor used.2. The apparent Km (at pH 8.1) for diaminodurene is 6·10?4 M and for diaminotoluene is 1.2·10?3 M. The concentrations of diaminodurene and diaminotoluene required to saturate the electron transport processes are > 2 mM and > 5 mM, respectively. At these higher electron donor concentrations the rates of electron transport are markedly increased by phosphorylation (1.5-fold) or by uncoupling conditions (2-fold).3. Kinetic analysis of the transfer of electrons from reduced 2,6-dichlorophenolindophenol (DCIPH2) to methylviologen indicates that two reactions with very different apparent Km values for DCIPH2 are involved. The rates of electron flux through both pathways are increased by phosphorylation or uncoupling conditions although only one of the pathways is coupled to ATP formation. No similar complications are observed when diaminodurene or diaminotoluene serves as the electron donor.4. In the diaminodurene → methylviologen reaction, ATP formation and that part of the electron transport dependent upon ATP formation are partially inhibited by the energy transfer inhibitor HgCl2. This partial inhibition of ATP formation rises to about 50% at less than 1 atom of mercury per 20 molecules of chlorophyll, then does not further increase until very much higher levels of mercury are added.5. It is suggested that exogenous electron donors such as diaminodurene, diaminotoluene and DCIPH2 can substitute for an endogenous electron carrier in donating electrons to cytochrome f via the mercury-sensitive coupling site (Site I) located on the main electron-transporting chain. If this is so, there would seem to be no reason for postulating yet another coupling site on a side branch of the electron transport chain in order to account for cyclic photophosphorylation.  相似文献   

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