Structure and Mechanism of Action of a Membrane-Bound Enzyme: Chloroplast Coupling Factor
In all organisms a transmembrane pH gradient is utilized as the source of free energy for the synthesis of ATP from ADP and Pi (1). The membrane-bound enzymes (coupling factors) that catalyze the synthesis and pump protons are remarkably similar from all sources: The basic structure consists of a ball on the surface of the membrane (F1) attached to a stalk (F0) that passes through the membrane. The minimal structure consists of five types of polypeptide chains in F1, probably in the stoichiometry α 3 β 3 γδε,and three types of polypeptide chains in F0, with the stoichiometry still controversial. F1 is an ATPase and contains all of the nucleotide binding sites but of course cannot make ATP catalytically when separated from the membrane. F0 is a hydrophobic structure that probably serves as the proton channel.
KeywordsHydrolysis Anisotropy Tyro Sine Catalysis Polypeptide
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