The F-ATPase is found in bacterial plasma membranes, mitochondrial inner membranes and in chloroplast thylakoid membranes. It has also been found in the archaea Methanosarcina barkeri. It uses a proton gradient to drive ATP synthesis and hydrolyzes ATP to build the proton gradient. The extrinisic membrane domain, F1, is composed of alpha, beta, gamma, delta, and epsilon subunits with a stoichiometry of 3:3:1:1:1. Alpha and beta subunit form the globular catalytic moiety, a hexameric ring of alternating subunits. Gamma, delta and epsilon subunits form a stalk, connecting F1 to F0, the integral membrane proton translocating domain. In bacteria, which is lacking a eukaryotic epsilon subunit homolog, this subunit is called the epsilon subunit.
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