The mitochondrial F1Fo ATP synthase

Adenosine triphosphate (ATP) is the general energy currency of living organisms from simple prokaryotes to the more complex eukaryotes. It is continually produced at the expense of nutrients and utilized by endergonic biological processes in large amounts that usually exceed the weight of the organism. In aerobic prokaryotic and eukaryotic cells, although some ATP is produced by soluble enzymes, the largest proportion comes from oxidative phosphorylation of coupling membranes. Oxidative phosphorylation is an integrated process in which the free energy, made available by downhill electron flow in the respiratory chain as a transmembrane electrochemical gradient of protons (DmHþ or protonmotive force (PMF)), is utilized by the F1Fo ATP synthase complex to make ATP from ADP (adenosine diphosphate) and Pi (inorganic phosphate). The F1Fo ATP synthase, also known as complex V, is a proton pump that converts the PMF into mechanochemical energy to drive ATP synthesis. When the PMF becomes limiting, as in extremely hypoxic conditions, the ATP synthase is reversed and it hydrolyzes ATP produced essentially by glycolysis until the PMF is reestablished