Multiple sites of interaction between the ATPase inhibitor and mitochondrial membrane from rat liver mitochondria

The ATPase inhibitor interacts with F₁-ATPase and sonicated submitochondrial particles in which the matrix side of the inner membrane is exposed to the suspending medium. On the other hand, preincubating the inhibitor with intact mitochondria in the presence of Mg⁺⁺-ATP greatly stimulates ATP-P1 exchange activity of the intact mitochondria. In contrast, preincubating the inhibitor with submitochondrial particles has no effect on the ATP-Pi exchange activity of the latter. Furthermore, when the inhibitor is incorporated inside the sumitochondrial particles by sonicating intact mitochondria in the presence of added inhibitor, the ATP-PI exchange activity of the so prepared submitochondrial particles is higher than that of control submitochondrial particles. When atractyloside is included in the assay medium, the ATP-Pi exchange activities of intact mitochondria (regardless of preincubation with added inhibitor or not) are completely inhibited while that of submitochondrial particles (regardless of preincorporating the inhibitor inside the particles or not) are not affected. These results indicate that the inhibitor interacts with F₁-ATPase on the matrix side and with the adenine nucleotide translocator on the outer side of the inner mitochondrial membrane.