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. 1983 Jun;72(2):313–320. doi: 10.1104/pp.72.2.313

Evidence for Cyclic Photophosphorylation during 14CO2 Fixation in Intact Chloroplasts

Studies with Antimycin A, Nitrite, and Oxaloacetate

K C Woo 1
PMCID: PMC1066230  PMID: 16662999

Abstract

This study examines the effect of antimycin A and nitrite on 14CO2 fixation in intact chloroplasts isolated from spinach (Spinacia oleracea L.) leaves. Antimycin A (2 micromolar) strongly inhibited CO2 fixation but did not appear to inhibit or uncouple linear electron transport in intact chloroplasts. The addition of small quantities (40-100 micromolar) of nitrite or oxaloacetate, but not NH4Cl, in the presence of antimycin A restored photosynthesis. Antimycin A inhibition, and the subsequent restoration of photosynthetic activities by nitrite or oxaloacetate, was observed over a wide range of CO2 concentration, light intensity, and temperature. High O2 concentration (up to 240 micromolar) did not appear to influence the extent of the inhibition by antimycin A, nor the subsequent restoration of photosynthetic activity by nitrite or oxaloacetate. Studies of O2 exchanges during photosynthesis in cells and chloroplasts indicated that 2 micromolar antimycin A stimulated O2 uptake by about 25% while net O2 evolution was inhibited by 76%. O2 uptake in chloroplasts in the presence of 2 micromolar antimycin A was 67% of total O2 evolution. These results suggest that only a small proportion of the O2 uptake measured was directly linked to ATP generation. The above evidence indicates that cyclic photophosphorylation is the predominant energy-balancing reaction during photosynthesis in intact chloroplasts. On the other hand, pseudocyclic O2 uptake appears to play only a minimal role.

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Selected References

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