The ATP synthase: the understood, the uncertain and the unknown

The F-ATPases, or F₁F_o-ATPases, are multisubunit enzyme complexes found in energy transducing membranes in eubacteria, mitochondria and chloroplasts. Their role is to synthesize ATP from ADP and phosphate under aerobic conditions using the proton-motive force generated by respiration or photosynthesis as a source of energy. The ATP hydrolase activities of the enzymes from mitochondria, chloroplasts and some eubacteria are inhibited, and they can only synthesize ATP. However, other eubacterial enzymes hydrolyze ATP, made by glycolysis under anaerobic conditions, to generate the proton motive force required for essential cellular functions, such as chemotaxis and transmembrane transport processes. The lecture will describe the common features and differences between the F-ATPases from these various sources. It has been assumed widely that information from one F-ATPase would apply to all or many other F-ATPases, but it is increasingly evident that while there are common principles in the operation of F-ATPases from diverse sources, there are also significant differences. This is most evident in the variety of the symmetries of the membrane bound c-rings in the rotors of the enzyme from various species, which has profound consequences for the bioenergetic cost of making ATP ¹.