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.