ATP-synthase of Rhodobacter capsulatus: coupling of proton flow through F-0 to reactions in F-1 under the ATP synthesis and slip conditions

A stepwise increasing membrane potential was generated in chromatophores of the phototrophic bacterium Rhodobacter capsulatus by illumination with sho rt flashes of light, Proton transfer through ATP-synthase (measured by elec trochromic carotenoid bandshift and by pH-indicators) and ATP release (meas ured by luminescence of luciferin-luciferase) mere monitored. The ratio bet ween the amount of protons translocated by F0F1 and the ATP yield decreased ,vith the flash number from an apparent value of 13 after the first flash t o about 5 when averaged over three flashes, In the absence of ADP, protons slipped through F0F1, The proton transfer through F0F1 after the first flas h contained two kinetic components, of about 6 ms and 20 ms both under the ATP synthesis conditions and under slip, The slower component of proton tra nsfer was substantially suppressed in the absence of ADP, We attribute our observations to the mechanism of energy storage in the ATP-synthase needed to couple the transfer of four protons with the synthesis of one molecule o f ATP, Most probably, the transfer of initial protons of each tetrad create s a strain in the enzyme that slows the translocation of the following prot ons, (C) 1999 Federation of European Biochemical Societies.