ATP Synthase: Two rotary molecular motors working together

ATP synthaseÑalso called FoF1 ATPase, or simply F-ATPaseÑis the universal protein that terminates oxidative phosphorylation by synthesizing ATP from ADP and phosphate. Nearly identical proteins are found in eukaryotic mitochondria and bacteria, and they all operate on the same principle. Electron driven ion pumps set up concentration and electrical gradients across a membrane. ATP synthase utilizes the energy stored in this electrochemical gradient to drive nucleotide synthesis. It does this in a surprising way: by converting the electromotive force into a rotary torque that is used to promote phosphate binding and to liberate ATP from the catalytic site where it was formed. Remarkably, this process can be reversed in certain circumstances: ATP hydrolysis can drive the engine in reverse so that F-ATPase functions as a proton pump. Indeed, the vacuolar V-ATPasesÑthe most ubiquitous intracellular proton pumpsÑare structurally similar to ATP synthase and appear to operate according to the same principles.