Dependence of the proton translocation stoichiometry of cyanobacterial and chloroplast H +-ATP synthase on the membrane composition

Abstract

The high proton translocation stoichiometry (approx. 9 H + / ATP) of ATPase proteoliposomes reconstituted from a thermophilic cyanobacterium (Van Walraven et al. (1986) FEBS Lett. 208, 138–142) has also been observed with chloroplast ATP synthase when reconstituted with cyanobacterial lipids. Both enzyme complexes in isolated and reconstituted form show highest stable trypsin-activated ATP hydrolysis activity at the same temperature (55°C). Also, both isolated ATP synthases require the same reconstitution procedure for maximal coupling quality. The proton translocation stoichiometry has been deduced from the relation between the initial rates of ATP hydrolysis at varying sizes of the electrochemical potential gradient ( Δ \\ ̄ gm H + ). A Δ \\ ̄ gm H + was imposed by valinomycin-induced K + diffusion potentials or by base-pulses which were equally efficient in inhibiting ATP hydrolysis. Kinetic experiments with the use of the pH indicator Cresol red confirm the high proton translocation stoichiometry of both types of ATPase proteoliposome. Functional co-reconstitution of both types of ATPase proteoliposome with cyanobacterial cytochrome b 6 f complex leads to a decrease in proton translocation stoichiometry to about 7 H + / ATP. Cyanobacterial membrane vesicles take up 4.4 protons per ATP hydrolyzed. A value of 4.5 H + / ATP is observed with chloroplasts in equilibrium (Gräber, P., Junesch, U. and Thulke, G. (1986) in Progress in Photosynthesis Research (Biggins, J., ed.), pp. 177–184, Martinus Nijhoff, Dordrecht). These results indicate that the proton translocation stoichiometry of the ATP synthase depends on the membrane composition. The consequence of this finding for the mechanism of proton translocation and the possible physiological relevance are discussed.