ATP SYNTHESIS IN CHROMATOPHORES DRIVEN BY ARTIFICIALLY INDUCED ION GRADIENTS

An electrochemical potential difference for protons (DELTA-approximately-mu-H+) across the membrane of bacterial chromatophores was induced by an artificially generated pH difference (DELTA-pH) and a K+/valinomycin diffusion potential, DELTA-phi. The initial rate of ATP synthesis was measured with a rapid-mixing quenched-flow apparatus in the time range between 70 ms and 30 s after the acid-base transition. The rate of ATP synthesis depends exponentially on DELTA-pH. Increasing diffusion potentials shift the DELTA-pH dependency to lower DELTA-pH values. Diffusion potentials were calculated from the Goldman equation. Using estimated permeability coefficients, the rate of ATP synthesis depends only on the electrochemical potential difference of protons irrespective of the relative contribution of DELTA-pH and DELTA-phi.