STUDIES ON THE MECHANISM OF OXIDATIVE-PHOSPHORYLATION - ATP SYNTHESIS BY SUBMITOCHONDRIAL PARTICLES INHIBITED AT F(0) BY VENTURICIDIN AND ORGANOTIN COMPOUNDS

Oligomycin, N,N'-dicyclohexylcarbodiimide (DCCD), venturicidin, and tetracoordinate organotin compounds (R3SnX) are potent inhibitors of the mitochondrial ATP synthase complex, all acting on the membrane sector, F0. Oligomycin and DCCD inhibit proton translocation through F0 and energy transfer between F0 and the catalytic sector, F1, of the ATP synthase complex. Our results have shown that venturicidin and organotin compounds (tributyltin and triphenyltin chloride were used) greatly attenuate these processes, but do not cause complete inhibition. As a result, bovine submitochondrial particles (SMP) treated with venturicidin or tributyltin chloride were shown to be capable of ATP hydrolysis and synthesis, albeit at very slow rates. We had shown previously that in ATP synthesis V(max) and apparent K(m) for ADP and P(i) increase or decrease, respectively, as the steady-state membrane potential is elevated or lowered (Matsuno-Yagi, A., and Hatefi, Y. (1986) J. Biol. Chem. 261, 14031-14038). These changes occurred at constant V(max)/K(m) suggesting that the apparent K(m) changes were due mainly to k(cat), changes. Results presented here show that, in respiring SMP treated with venturicidin or organotin compounds, the membrane potential is near the static-head level, but the slow rate of ATP synthesis takes place with a low K(m)ADP value of 2-3 muM. In agreement with our previous conclusions, these results indicate that it is not the membrane potential per se that affects K(m)ADP during ATP synthesis, but rather it is the rate of energy transfer from F0 to F1 that influences both V(max) and K(m)ADP. Further conclusions from the above studies have been discussed in relation to the possible mechanism of energy transfer between F0 and F1 and the manner in which venturicidin and organotin compounds might attenuate this process.