The rate of ATP-synthesis as a function of ΔpH and Δψ catalyzed by the active, reduced H +-ATPase from chloroplasts

Abstract

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, ΔpH, combined with a K +/valinomycin diffusion potential, Δψ. 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 ΔpH. Increasing diffusion potentials shifts the ΔpH-dependencies to lower ΔpH 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 ΔpH and Δψ.