Kinetics of the membrane-bound inorganic pyrophosphatase from Rhodospirillum rubrum chromatophores Effect of the transmembrane electrical potential on the rate constants

AbstractThe behaviour of the membrane-bound proton-translocating pyrophosphatase (H+-PPase) in Rhodospirillum rubrum chromatophores upon application of an electrochemical potential is studied. The rate constants are shown to be affected in an asymmetric fashion. The forward rate constant (PPi synthesis) is shown to be at least 45-times larger during illumination than when there is no proton-motive force. The hydrolysis rate is increased maximally 8-times when the potential is dissipated. The effect of the electrical field gradient is thus mainly to increase the forward rate of the reaction. The H+-PPase also seems to be a functionally simpler enzyme than the H+-ATPase, lacking the hydrolysis activation step during energization found in the latter