ATP synthase of chloroplasts: selective action of agents binding to F1 on partial reactions of proton transfer in F0.

We studied the basic steps of proton transfer through ATP synthase of chloroplasts, CF0CF1, under conditions of proton slip, a conducting stage in the absence of added nucleotides. On the background of a steady transmembrane pH difference, voltage steps were induced by flashing light. Proton intake, transfer, and release by CF0CF1 were kinetically resolved by spectrophotometric probes. Kinetic disparities between these three steps were observed. Rapid but limited proton intake from the thylakoid lumen and proton release into the medium (tau 1/2 approximately 5 ms) preceded charge transfer across the dielectric barrier in the enzyme (tau 1/2 approximately 30 ms). The saturation behavior under multiple flashes suggested a sequential reaction mechanism. ADP and dequalinium, when bound to subunit beta of the catalytic portion, CF1, blocked different partial reactions involving protons. ADP in the catalytic cleft blocked the electrogenic transfer step, and dequalinium at the adjacent DELSEED sequence on the same subunit blocked the release of protons. Both effects prove a long-range conformational transmission between remote (approximately 10 nm) domains on F1 and on F0. For the normal sequence of events from protons to ATP they suggest a specific action of certain proton-transfer steps on different domains of the catalytic portion.