Relationship between the Level of Adenine Nucleotides and the Carboxylation Activity of Illuminated Isolated Spinach Chloroplasts: A Study with Antimycin A.

The changes in the levels of intact spinach (Spinacia oleracea L.) chloroplast adenine nucleotides during the time course of light-dependent CO(2) fixation were determined with respect to the effect of antimycin A. This study demonstrated that antimycin A lowered the rate of ATP formation during the induction period of carboxylation. While the steady state levels of ATP and the energy-charge value also decreased in the presence of antimycin, the concomitant increase of the CO(2) fixation activities insured higher ATP turnover rates. Changes in the labeling of CO(2) fixation products during the lag phase suggested a stepwise activation of the Calvin cycle, with fructose 1,6-diphosphate, and ribulose 5-phosphate kinase being activated before ribulose 1,5-diphosphate carboxylase. The possible mechanisms of the enhancement of CO(2) fixation activity by antimycin A in relation to its action on photophosphorylation during the lag phase are discussed.