KINETICS AND ENERGETICS OF REDOX REGULATION OF ATP SYNTHASE FROM CHLOROPLASTS

The rate of ATP hydrolysis catalyzed by the membrane-bound CF0F1 ATP s ynthase from chloroplasts served as a probe for the determination of t he reduction grade of the enzyme treated with dithiothreitol (DTT) or thioredoxin. Rate constants for reduction were obtained. It turns out that reduction by thioredoxin is about a factor of 6,000 more effectiv e than DTT reduction. The activation profiles with respect to DELTApH were obtained for reduced and oxidized ATPases. The activation curve o f reduced enzyme turns out to have its half-maximum degree of activati on at DELTApH = 1.65, which is considerably lower than reported hither to. The corresponding value of the oxidized enzyme has been obtained f rom the rate of ATP hydrolysis in the case of incomplete reduced ATPas es, taking into account the aforementioned rate constants, and comes t o DELTApH = 3.35.