Contents of endogenous adenine nucleotides and ATPase activity of isolated whole chloroplasts

Abstract

Endogenous adenine nucleotide contents of isolated intact chloroplasts and activities of the H +-ATPase were measured in parallel under various experimental conditions. In chloroplasts isolated from spinach grown in summer, ATPase activity declines upon light-dark transition in a biphasic manner. Initial rapid inactivation of about 50% of the ATPases corresponds with the rapid increase of the ADP and decrease of the ATP levels. The residual ATPases are slowly deactivated, probably due to the reversal of thiol modulation. In isolated chloroplasts from winter plants the phase of rapid inactivation is largely absent. Those chloroplasts have a low content of endogenous nucleotides. When the ratio of internal ATP ADP is decreased by the addition of 3-phosphoglycerate or the uncoupler FCCP, the activity of the ATPase decreases. The relationship between activity and ATP ADP ratio is nearly linear. Inorganic phosphate, although being ineffective in changing the internal nucleotide levels, significantly raises the ATPase activity. The results suggest that in whole chloroplasts the ATPase not only is regulated by the thioredoxin system but also controlled by the internal ATP ADP ratio. This kind of control is referred to the nucleotide-dependent regulatory mechanism previously demonstrated in isolated thylakoid suspension.