H-ATPASE AND H+-PYROPHOSPHATASE OF THE YEAST VACUOLAR MEMBRANE()

Saccharomyces carlsbergensis vacuoles possess an ATPase differing wide ly in properties from the well-known ATPases of plasma membranes and m itochondria as well as from other vacuolar phosphohydrolases. The yeas t vacuolar ATPase is an electrogenic H+-translocase. The H+-ATPase can be incorporated into liposomes in functionally active form. The tonop last ATPase does not form a phosphorylated intermediate. The purified vacuolar ATPase contains three main polypeptides with molecular masses of 72, 62, and 16 kD. S. carlsbergensis vacuoles possess pyrophosphat ase (PPase) activity as well, also differing widely in properties from other phosphohydrolases of vacuoles. The vacuolar membrane-bound PPas e is a proton pump. The apparent molecular weight of the membrane-boun d PPase is 120 kD and its molecule consists of three equivalent 41-kD subunits. The soluble PPase from vacuolar sap has a molecular weight o f about 82 kD and consists of three equivalent 28-kD subunits.