The rate of ATP-synthesis as a function of delta pH and delta psi catalyzed by the active, reduced H(+)-ATPase from chloroplasts.

The H(+)-ATPase from chloroplasts was brought into the active, reduced state. Then, an electrochemical potential difference of protons across the thylakoid membranes was generated by an acid-base transition, delta pH, combined with a K+/valinomycin diffusion potential, delta psi. The initial rate of ATP synthesis was measured with a rapid-mixing quenched-flow apparatus in the time-range between 20-150 ms. The rate of ATP synthesis depends in a sigmoidal way on delta pH. Increasing diffusion potentials shifts the delta pH-dependencies to lower delta pH values. Analysis of the data indicate that the rate of ATP synthesis depends on the electrochemical potential difference of protons irrespective of the relative contribution of delta pH and delta psi.