KINETICS OF PROTON-TRANSPORT-COUPLED ATP SYNTHESIS IN CHLOROPLASTS - ACTIVATION OF THE ATPASE BY AN ARTIFICIALLY GENERATED DELTA-PH AND DELTA-PSI

The kinetics of proton transport coupled ATP synthesis at the chloroplast membrane was investigated upon energization of the membrane by an artificially generated DELTA pH and an electric potential difference, DELTA PSI . Using a rapid mixing system, rates of ATP synthesis were studied at short reaction times ( less than 150 ms) where all relevant parameters ( DELTA pH, DELTA PSI , substrate and product concentrations) remain practically constant at their initial values. Under these conditions it was found: 1. The maximal rate of ATP synthesis obtained under these artificial conditions is the same as that obtained by light-induced ATP synthesis. 2. The turnover number of the ATPase is 410 s** minus **1. 3. The rate of ATP synthesis depends in a sigmoidal way on the transmembrane electrochemical potential difference of protons, DELTA OVER BAR //H// plus , regardless of the relative contributions by DELTA pH and DELTA PSI .