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1.
Starch degradation with a rate of 1 to 2 microgram-atom carbon per milligram chlorophyll per hour was monitored in the isolated intact spinach ( Spinacia oleracea) chloroplast which had been preloaded with 14C-starch photosynthetically from 14CO 2. Starch breakdown was dependent upon inorganic phosphate and the 14C-labeled intermediates formed were principally those of the Embden-Meyerhof pathway from glucose phosphate to glycerate 3-phosphate. In addition, isotope was found in ribose 5-phosphate and in maltose and glucose. The appearance of isotope in the intermediates of the Embden-Meyerhof pathway but not in the free sugars was dependent upon the inorganic phosphate concentration. Dithiothreitol shifted the flow of 14C from triose-phosphate to glycerate 3-phosphate. Iodoacetic acid inhibited starch breakdown and caused an accumulation of triose-phosphate. This inhibition of starch breakdown was overcome by ATP. The inhibitory effect of ionophore A 23187 on starch breakdown was reversed by the addition of magnesium ions. The formation of maltose but not glucose was impaired by the ionophore. The inhibition of starch breakdown by glycerate 3-phosphate was overcome by inorganic phosphate. Fructose 1,6-bisphosphate and ribose 5-phosphate did not affect the rate of polysaccharide metabolism but increased the flow of isotope into maltose. Starch breakdown was unaffected by the uncoupler (trifluoromethoxyphenylhydrazone), electron transport inhibitors (rotenone, cyanide, salicylhydroxamic acid), or anaerobiosis. Hexokinase and the dehydrogenases of glucose 6-phosphate and gluconate 6-phosphate were detected in the chloroplast preparations. It was concluded ( a) that chloroplastic starch was degraded principally by the Embden-Meyerhof pathway and by a pathway involving amylolytic cleavage; ( b) ATP required in the Embden-Meyerhof pathway is generated by substrate phosphorylation in the oxidation of glyceraldehyde 3-phosphate to glycerate 3-phosphate; and ( c) the oxidative pentose phosphate pathway is the probable source of ribose 5-phosphate. 相似文献
2.
The light-dependent synthesis of glycolate derived from fructose 1,6-diphosphate, ribose 5-phosphate, or glycerate 3-phosphate was studied in the intact spinach (Spinacia oleracea) chloroplasts in the absence of CO(2). Glycolate yield increased with an elevation of O(2), pH, and the concentration of the phosphorylated compound supplied. No pH optimum was observed as the pH was increased from 7.4 to 8.5. The average maximal rate of glycolate synthesis was 50 mumoles per milligram chlorophyll per hour while the highest rate observed was 92 with 2.5 mm fructose 1,6-diphosphate in 100% O(2). The highest yields of glycolate synthesized from fructose 1,6-diphosphate, ribose 5-phosphate, or glycerate 3-phosphate were 0.14, 0.24, and 0.30, respectively, on a molar basis. 相似文献
3.
Young expanding spinach leaves exposed to 14CO 2 under physiological conditions for up to 20 minutes assimilated CO 2 into lipids at a mean rate of 7.6 micromoles per milligram chlorophyll per hour following a lag period of 5 minutes. Label entered into all parts of the lipid molecule and only 28% of the 14C fixed into lipids was found in the fatty acid moieties, i.e. fatty acids were synthesized from CO 2in vivo at a mean rate of 2.1 micromoles per milligram chlorophyll per hour. Intact spinach chloroplasts isolated from these leaves incorporated H 14CO 3 into fatty acids at a maximal rate of 0.6 micromole per milligram chlorophyll per hour, but were unable to synthesize either the polar moieties of their lipids or polyunsaturated fatty acids. Since isolated chloroplasts will only synthesize fatty acids at rates similar to the one obtained with intact leaves in vivo if acetate is used as a precursor, it is suggested that acetate derived from leaf mitochondria is the physiological fatty acid precursor. 相似文献
4.
Previously, C Baysdorfer and JM Robinson (1985 Plant Physiol 77: 318-320) demonstrated that, in a reconstituted spinach chloroplast system, NADP photoreduction functioning at most maximal rate and reductant demand, was the successful competitor with NO 2− photoreduction for reduced ferredoxin. This resulted in a repression of NO 2− reduction until all NADP available had been almost totally reduced. Further experiments, employing isolated, intact spinach leaf plastids and soybean leaf mesophyll cells, were conducted to examine competition for reductant between CO 2 and NO 2− photoassimilation, in situ. In isolated, intact plastid preparations, regardless of whether the demand for reductant by CO 2 photoassimilation was high (5 millimolar `CO 2') with rates of CO 2 fixation in the range 40 to 90 micromoles CO 2 fixed per hour per milligram chlorophyll, low (0.5 millimolar `CO 2') with rates in the range 5 to 8 micromoles CO 2 per hour per milligram chlorophyll, or zero (no `CO 2'), NO 2− photoreduction displayed equal rates in the range of 8 to 22 micromoles per hour per milligram chlorophyll. In the absence of `CO 2', but in the presence of saturating white light, 3-phosphoglycerate photoreduction at rates of 82 to 127 micromoles per hour per milligram chlorophyll did not repress, and occasionally stimulated concomitant rates of NO 2− reduction which ranged from 23.4 to 38.5. Conversely, in plastid preparations, NO 2− at levels of 50 to 100 micromolar, stimulated plastid CO 2 fixation when `CO 2' was saturating with respect to carboxylation. Further, levels of NO 2− in the range 250 to 2500 micromolar, stimulated soybean leaf mesophyll cell net CO 2 fixation as much as 1.5-fold if `CO 2' was saturating with respect to CO 2 fixation. It appeared likely that, in high light in vivo, CO 2 and NO 2− photoassimilatory processes are not forced to intercompete for reduced ferredoxin in the intact chloroplast. 相似文献
5.
Isolated spinach ( Spinacia oleracea L. var. Bloomsdale) leaf protoplasts reduced nitrate at rates of 9 micromoles per milligram chlorophyll per hour in light with a 3- to 4-fold stimulation in the presence of HCO 3−. A similar stimulation of nitrate reduction in the absence of CO 2 fixation was obtained by the addition of malate, oxaloacetate (OAA), phospho-3-glyceric acid (PGA), or dihydroxyacetone phosphate (DHAP). Stimulation by malate and DHAP was light-independent, while the PGA and OAA effect was light-dependent. Nitrate reduction was found to be coupled to the cytoplasmic oxidation of DHAP or malate. The PGA/DHAP and OAA/malate shuttle across the chloroplast envelope has been demonstrated to support CO 2 fixation and/or nitrate reduction. The leaf protoplasts readily assimilated nitrate into amino-N in a stoichiometric relationship. 相似文献
6.
Using partially purified sedoheptulose-1,7-bisphosphatase from spinach ( Spinacia oleracea L.) chloroplasts the effects of metabolites on the dithiothreitoland Mg 2+-activated enzyme were investigated. A screening of most of the intermediates of the Calvin cycle and the photorespiratory pathway showed that physiological concentrations of sedoheptulose-7-phosphate and glycerate specifically inhibited the enzyme by decreasing its maximal velocity. An inhibition by ribulose-1,5-bisphosphate was also found. The inhibitory effect of sedoheptulose-7-phosphate on the enzyme is discussed in terms of allowing a control of sedoheptulose-1,7-bisphosphate hydrolysis by the demand of the product of this reaction. Subsequent studies with partially purified fructose-1,6-bisphosphatase from spinach chloroplasts showed that glycerate also inhibited this enzyme. With isolated chloroplasts, glycerate was found to inhibit CO 2 fixation by blocking the stromal fructose-1,6-bisphosphatase. It is therefore possible that the inhibition of the two phosphatases by glycerate is an important regulatory factor for adjusting the activity of the Calvin cycle to the ATP supply by the light reaction.Abbreviations DTT
dithiothreitol
- FBPase
fructose-1,6-bisphosphatase
- Fru-1,6-P 2
fructose-1,6-bisphosphate
- Fru-6-P
fructose-6-phosphate
- 3-PGA
3-phosphoglycerate
- Ru-1,5-P 2
ribulose-1,5-bisphosphate
- Ru-5-P
ribulose-5-phosphate
- SBPase
sedoheptulose-1,7-bisphosphatase
- Sed-1,7-P 2
sedoheptulose-1,7-bisphosphate
- Sed-7-P
sedoheptulose-7-phosphate
This work was supported by the Deutsche Forschungsgemein-schaft. 相似文献
7.
Light-dependent O 2 reduction concomitant with O 2 evolution, ATP formation, and NADP reduction were determined in isolated spinach ( Spinacia oleracea L. var. America) chloroplast lamellae fortified with NADP and ferredoxin. These reactions were investigated in the presence or absence of catalase, providing a tool to estimate the reduction of O 2 to H 2O 2 (Mehler reaction) concomitant with NADP reduction. In the presence of 250 micromolar O 2, O 2 photoreduction, simultaneous with NADP photoreduction, was dependent upon light intensity, ferredoxin, Mn 2+, NADP, and the extent of coupling of phosphorylation to electron flow. In the presence of an uncoupling concentration of NH4+, saturating light intensity (>500 watts/square meter), saturating ferredoxin (10 micromolarity) rate-limiting to saturating NADP (0.2-0.9 millimolarity), and Mn2+ (50-1000 micromolarity), the maxium rates of O2 reduction were 13-25 micromoles/milligram chlorophyll per hour, while concomitant rates of O2 evolution and NADP reduction were 69 to 96 and 134 to 192 micromoles/milligram chlorophyll per hour, respectively. Catalase did not affect the rate of NADPH or ATP formation but decreased the NADPH:O2 ratios from 2.3-2.8 to 1.9-2.1 in the presence of rate-limiting as well as saturating concentrations of NADP. Photosynthetic electron flow at a rate of 31 micromoles O2 evolved/milligram chlorophyll per hour was coupled to the synthesis of 91 micromoles ATP/milligram chlorophyll per hour, while the concomitant rate of O2 reduction was 0.6 micromoles/milligram chlorophyll per hour and was calculated to be associated with an apparent ATP formation of only 2 micromoles/milligram chlorophyll per hour. Thus, electron flow from H2O to O2 did not result in ATP formation significantly above that produced during NADP reduction. 相似文献
8.
The response of the Benson-Calvin cycle to changes in irradiance and photoinhibition was measured in low-light grown barley ( Hordeum vulgare) leaves. Upon the transition from the growth irradiance (280 micromoles per square meter per second) to a high photoinhibitory irradiance (1400 micromoles per square meter per second), the CO 2 assimilation rate of the leaves doubled within minutes but high irradiance rapidly caused a reduction in quantum efficiency. Following exposure to high light the activities of NADP-malate dehydrogenase and fructose-1,6-bisphosphatase obtained near maximum values and the activation state of ribulose-1,5-bisphosphate carboxylase increased. The activity of the latter remained constant throughout the period of photoinhibitory irradiance, but the increase in the activities of fructose-1,6-bisphosphatase and NADP-malate dehydrogenase was transient decreasing once more to much lower values. This suggests that immediately following the transition to high light reduction and activation of redox-modulated enzymes occurred, but then the stroma became relatively oxidized as a result of photoinhibition. The leaf contents of glucose 6-phosphate and fructose 6-phosphate increased following exposure to high light but subsequently decreased, suggesting that following photoinhibition sucrose synthesis exceeded the rate of carbon assimilation. The ATP content attained a constant value much higher than that in low light. During photoinhibition the glycerate 3-phosphate content greatly increased while ribulose-1,5-bisphosphate decreased. The fructose-1,6-bisphosphate and triose phosphate contents increased initially and then remained constant. During photoinhibition CO 2 assimilation was not limited by ribulose-1,5-bisphosphate carboxylase activity but rather by the regeneration of the substrate, ribulose-1,5-bisphosphate, related to a restriction on the supply of reducing equivalents. 相似文献
9.
Chloroplasts isolated from synchronous cultures of the unicellular green alga Chlamydomonas reinhardii, SAG 11-32/b (−), fix CO 2 at rates between 25 and 50 micromoles per milligram chlorophyll per hour. The upper value is approximately half of the rate of the intact cell. During storage in the dark on ice, the chloroplast preparation loses 30 to 50% of its CO2 fixing capability per hour. Under reducing conditions (+ 1 millimolar dithiothreitol), this loss of activity is about twice as fast. The same reducing conditions stimulate CO2 fixation in the light. High concentrations of inorganic phosphate (>2 millimolar) inhibit CO2 fixation. This inhibition is overcome by the addition of glycerate 3-phosphate. It is concluded that chloroplasts from C. reinhardii possess a higher plant type phosphate translocator. With respect to dependency upon light intensity, pH and Mg2+ concentration, the results were similar to that reported for chloroplasts from higher plants. However, in contrast to higher plant chloroplasts, maximum CO2 fixation is observed at the relatively low osmotic concentration of 0.12 molar mannitol in the reaction buffer. 相似文献
10.
A system has been developed for the isolation of photosynthetically active chloroplasts from leaves of Populus deltoides. A high proportion of the chloroplasts appeared intact. The maximum rates of different photosynthetic processes were as follows: CO 2 fixation 3.5 micromoles per milligram chlorophyll per hour, noncyclic ATP synthesis 10 micromoles per milligram chlorophyll per hour, and cyclic ATP synthesis 300 micromoles per milligram chlorophyll per hour. 相似文献
11.
The effects of reduced osmotic potential on the photosynthetic carbon reduction cycle were investigated by monitoring photosynthetic processes of spinach ( Spinacia oleracea L. var. Long Standing Bloomsdale) chloroplasts exposed to increased assay medium sorbitol concentrations. CO 2 assimilation was found to be inhibited at 0.67 molar sorbitol by about 60% from control rates at 0.33 molar sorbitol. This level of stress inhibition was greater than that affecting the reductive phase of the cycle; glycerate 3-phosphate reduction was inhibited at 0.67 molar by 27 to 40%. Sorbitol (0.67 molar) inhibited the rate of O 2 evolution at saturating and limiting concentrations of NaHCO 3, and extended the lag phase of O 2 evolution. This indicated that factors which are rate-limiting to the photosynthetic process are adversely affected by reduced osmotic potential. Analysis of photosynthetic products following CO2 fixation in 0.33 molar sorbitol and 0.67 molar sorbitol indicated that reduced osmotic potential facilitated increases in the levels of fructose 1,6-bisphosphate and triose phosphates with reductions in glucose 6-phosphate and fructose 6-phosphate, implicating fructose 1,6-bisphosphatase as a site of osmotic stress. Osmotic inhibition of the reductive portion (glycerate 3-phosphate to triose phosphate) of the photosynthetic carbon reduction cycle was partially attributed to feedback inhibition by the product, triose phosphate, on glycerate 3-phosphate reduction. A saturating concentration of ribose 5-phosphate partially overcame osmotic inhibition of CO2-supported O2 evolution, indicating another but apparently less severe site of stress inhibition in the sequence of ribose 5-phosphate to glycerate 3-phosphate. 相似文献
12.
The regulatory metabolite fructose-2,6-bisphosphate (Fru-2,6-P 2) has an important function in controlling the intermediary carbon metabolism of leaves. Fru-2,6-P 2 controls two cytosolic enzymes involved in the interconversion of fructose-6-phosphate and fructose-1,6-bisphosphate (fructose-1,6-bisphosphatase and pyrophosphate, fructose-6-phosphate 1-phosphotransferase) and thereby controls the partitioning of photosynthate between sucrose and starch. It has been demonstrated that Fru-2,6-P 2 is present mainly in the cytosol. Here we present evidence that Fru-2,6-P 2 can be taken up by isolated intact chloroplasts but at a very slow rate (about 0.01 micromoles per milligram of chlorophyll per hour). This uptake is time and concentration dependent and is inhibited by PPi. When provided a physiological concentration of Fru-2,6-P 2 (10 micromolar), chloroplasts accumulated up to 0.6 micromolar Fru-2,6-P 2 in the stroma. Elevated plastid Fru-2,6-P 2 levels had no effect on overall photosynthetic rates of isolated chloroplasts. The results indicate that, while Fru-2,6-P 2 enters isolated chloroplasts at a sluggish rate, caution should be exercised in ascribing physiological importance to effects of Fru-2,6-P 2 on chloroplast enzymes. 相似文献
13.
A mass spectrometric method combining 16O/ 18O and 12C/ 13C isotopes was used to quantify the unidirectional fluxes of O 2 and CO 2 during a dark to light transition for guard cell protoplasts and mesophyll cell protoplasts of Commelina communis L. In darkness, O 2 uptake and CO 2 evolution were similar on a protein basis. Under light, guard cell protoplasts evolved O 2 (61 micromoles of O 2 per milligram of chlorophyll per hour) almost at the same rate as mesophyll cell protoplasts (73 micromoles of O 2 per milligram of chlorophyll per hour). However, carbon assimilation was totally different. In contrast with mesophyll cell protoplasts, guard cell protoplasts were able to fix CO 2 in darkness at a rate of 27 micromoles of CO 2 per milligram of chlorophyll per hour, which was increased by 50% in light. At the onset of light, a delay observed for guard cell protoplasts between O 2 evolution and CO 2 fixation and a time lag before the rate of saturation suggested a carbon metabolism based on phospho enolpyruvate carboxylase activity. Under light, CO 2 evolution by guard cell protoplasts was sharply decreased (37%), while O 2 uptake was slowly inhibited (14%). A control of mitochondrial activity by guard cell chloroplasts under light via redox equivalents and ATP transfer in the cytosol is discussed. From this study on protoplasts, we conclude that the energy produced at the chloroplast level under light is not totally used for CO 2 assimilation and may be dissipated for other purposes such as ion uptake. 相似文献
14.
Mesophyll cells and bundle sheath strands were isolated rapidly from leaves of the C 4 species Digitaria pentzii Stent. (slenderstem digitgrass) by a chopping and differential filtration technique. Rates of CO 2 fixation in the light by mesophyll and bundle sheath cells without added exogenous substrates were 6.3 and 54.2 micromoles of CO 2 per milligram of chlorophyll per hour, respectively. The addition of pyruvate or phosphoenolpyruvate to the mesophyll cells increased the rates to 15.2 and 824.6 micromoles of CO 2 per milligram of chlorophyll per hour, respectively. The addition of ribose 5-phosphate increased the rate for bundle sheath cells to 106.8 micromoles of CO 2 per milligram of chlorophyll per hour. These rates are comparable to those reported for cells isolated by other methods. The Km(HCO 3−) for mesophyll cells was 0.9 m m; for bundle sheath cells it was 1.3 m m at low, and 40 m m at higher HCO 3− concentrations. After 2 hours of photosynthesis by mesophyll cells in 14CO 2 and phosphoenolpyruvate, 88% of the incorporated 14C was found in organic acids and 0.8% in carbohydrates; for bundle sheath cells incubated in ribose 5-phosphate and ATP, more than 58% of incorporated 14C was found in carbohydrates, mainly starch, and 32% in organic acids. These findings, together with the stimulation of CO 2 fixation by phosphoenolpyruvate for mesophyll cells and by ribose 5-phosphate plus ATP for bundle sheath cells, and the location of phosphoenolpyruvate and ribulose bisphosphate carboxylases in mesophyll and bundle sheath cells, respectively, are in accord with the scheme of C 4 photosynthesis which places the Calvin cycle in the bundle sheath and C 4 acid formation in mesophyll cells. 相似文献
15.
Uptake of d, l-glycerate into the chloroplast stroma has been studied using the technique of silicone oil filtering centrifugation. Glycerate uptake was 3 to 5 times higher in the light than in darkness, the stimulation by light being abolished by the proton ionophore carbonyl cyanide p-trifluoromethoxyphenyl hydrazone. The pH optimum for uptake was 7.0 at 2°C and 8.5 at 20°C, but at all pH values the rate of uptake was higher at 20°C than at 2°C. Uptake was concentration dependent, saturating above 8 millimolar glycerate. At 2°C, the Km was 0.3 millimolar and the Vmax was 13 micromoles per milligram of chlorophyll per hour. At 20°C initial rates of glycerate uptake were higher than 40 micromoles per milligram of chlorophyll per hour. 相似文献
16.
This study examines the capacity of intact spinach ( Spinacia oleracea L.) chloroplasts to fix 14CO 2 when supplied with Benson-Calvin cycle intermediates in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). Under these conditions, substantial 14CO 2 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 14CO 2 fixation (20-40 micromoles per milligram chlorophyll per hour) was obtained with dihydroxyacetone phosphate. In contrast, no 14CO 2 fixation occurred when 3-phosphoglycerate was used. 14CO 2 fixation in the presence of dihydroxyacetone phosphate and DCMU was inhibited by carbonylcyanide m-chlorophenylhydrazone, dl-glyceraldehyde, and pyridoxal 5′-phosphate. Low concentrations of O 2 (25-50 micromolar) stimulated 14CO 2 fixation, but the activity decreased with increasing O 2 concentrations. The fixation of 14CO 2 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
17.
Intact spinach chloroplasts incorporated 35SO 42− into sulfoquinovosyldiacylglycerol in the dark at rates equivalent to those previously reported for illuminated chloroplasts provided that either ATP itself or an ATP-generating system was added. No additional reductant was necessary for SQDG synthesis by chloroplasts. The optimal concentration of ATP was between 2 and 3 millimolar. Rates of synthesis up to 2.6 nanomoles per milligram chlorophyll per hour were observed. UTP, GTP, and CTP could not substitute for ATP. Incubation of UTP with ATP (1:1) stimulated synthesis of sulfoquinovosyldiacylglycerol. No additional stimulation of the reaction was observed upon addition of other nucleoside triphosphates with ATP. For the generation of ATP in the chloroplast, addition of dihydroxyacetone phosphate alone did not promote synthesis of sulfoquinovosyldiacylglycerol, but in combination with inorganic phosphate and oxaloacetate, rates of synthesis up to 3.2 nanomoles per milligram chlorophyll per hour were observed. Dark synthesis was optimal in the presence of 2 millimolar dihydroxyacetone phosphate, 2 millimolar oxaloacetate, and 1 millimolar KH 2PO 4. 相似文献
18.
Chloroplasts isolated from Kalanchoe diagremontiana leaves were capable of photosynthesizing at a rate of 5.4 μmoles of CO 2 per milligram of chlorophyll per hour. The dark rate of fixation was about 1% of the light rate. A high photosynthetic rate was associated with low starch content of the leaves. Ribose 5-phosphate, fructose 1,6-diphosphate, and dithiothreitol stimulated fixation, whereas phosphoenolpyruvate and azide were inhibitors. The products of CO 2 fixation were primarily those of the photosynthetic carbon reduction cycle. 相似文献
19.
Crystalline ribulose 1,5-bisphosphate carboxylase-oxygenase (EC 4.1.1.39) was isolated from tobacco ( Nicotiana tabacum L.) leaf homogenates and the two competing reactions were examined for differential regulation in vitro by temperature pretreatment and chloroplast metabolites. Both the carboxylase and oxygenase activities were inactivated 50% by storing the dissolved protein at 0 °C and fully reactivated by heating the solution at 50 °C in the absence of Mg 2+ and a sulfhydryl reagent. When the heat-activated enzyme was preincubated with physiological levels of various chloroplast metabolites and CO 2 and the two reactions were assayed simultaneously in the same reaction vessel upon initiation with ribulose 1,5-bisphosphate, three classes of effectors were observed: (a) those which stimulated both activities (NADPH, 6-phosphogluco-bisphosphate gluconate, fructose 1,6-bisphosphate, 3-phosphoglycerate glycerate), (b) those which essentially had no effect (fructose 6-phosphate, glucose 6-phosphate), and (c) one, ribose 5-phosphate, which inhibited the two reactions. However, within the limits of experimental error, none of the metabolites examined produced a differential regulation of the ribulose 1,5-bisphosphate carboxylase-oxygenase activities. The similar response of the two competing activities to temperature pretreatment and various chloroplast metabolites is consistent with the notion that both reactions are associated with the same or adjacent catalytic sites on this bifunctional enzyme. 相似文献
20.
A spinach ( Spinacia oleracia var. America) chloroplast particle fortified with ferredoxin, fructose-1,6-bisphosphate, or ribose-5-phosphate and NADP has been shown to generate NADPH by the oxidation of glyceraldehyde-3 phosphate to glycerate-3-phosphate (PGA) and to reduce ferredoxin with the NADPH. The resulting reduced ferredoxin can reduce O 2 to H 2O 2, nitrite to ammonia, or protons to H 2. Hydrogen production was the result of adding hydrogenase from Chlamydomonas reinhardii to the chloroplast preparation. The predicted stoichiometry of 1 PGA:1 O 2 in the absence of and 2 PGA:1 O 2 in the presence of catalase was observed indicating H 2O 2 as the end product of O 2 reduction. The predicted stoichiometry of 3 PGA:1 nitrite:1 ammonia was also observed. A scheme is presented to account for a sustained generation of NADP and ATP necessary for the dissimilation of starch in the darkened chloroplast. The unifying term chloroplast respiration is introduced to account for those reactions in which reduced ferredoxin interacts with physiological acceptors other than NADP or nitrite, hydrogen, or O 2 respiration when nitrite, protons, or O 2 is the ultimate electron acceptor. 相似文献
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