The rate of ATP hydrolysis catalyzed by the membrane-bound CF0F1 ATP synthase from chloroplasts served as a probe for the determination of the 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 effective than DTT reduction. The activation profiles with respect to ΔpH were obtained for reduced and oxidized ATPases. The activation curve of reduced enzyme turns out to have its half-maximum degree of activation at ΔPH = 1.65, which is considerably lower than reported hitherto. The corresponding value of the oxidized enzyme has been obtained from the rate of ATP hydrolysis in the case of incomplete reduced ATPases, taking into account the aforementioned rate constants, and comes to ΔpH = 3.35.
