Exogenous energy supply to the plasma membrane of dark anaerobic cyanobacterium Anacystis nidulans: Thermodynamic and kinetic characterization of the ATP synthesis effected by an artificial proton motive force

Abstract

The net synthesis of ATP in dark anaerobic cells of Anacystis nidulans subjected to acid jumps and/or valinomycin pulses was characterized thermodynamically and kinetically. Maximum initial rates of 75 nmol ATP/min per mg dry weight at an applied proton motive force of −350 mV were obtained, the flow-force relationship (rate of ATP synthesis vs applied proton motive force) being linear between −240 and −320 mV irrespective of the source of the proton motive force. The pulse-induced ATP synthesis was inhibited by uncouplers (H + ionophores) and F 0F 1ATPase inhibitors but not by KCN or CO. In order to obtain maximum rates of pulse-induced ATP synthesis both a favorable stationary Δψ (−100 mV at pH o 9, preceding the acid jumps) and a favorable stationary ΔpH (+2 units at pH o 4.1, preceding the valinomycin pulse) of the plasma membrane were obligatory, the effects of Δψ and ΔpH being strictly additive. Moreover, the pulse-induced ATP synthesis required a minimum total proton motive force of −200 to −250 mV across the plasma membrane; it also required low preexisting phosphorylation potentials corresponding to −400 mV in dark anaerobic i.e., energy-depleted, cells. The results are discussed in terms of both a reversible H +-ATPase and a respiratory electron transport system occurring in the plasma membrane of intact Anacystis nidulans.