title: Functional molecular masses of vacuolar membrane H+-ATPase from Saccharomyces cerevisiae as studied by radiation inactivation analysis.
abstract: The functional molecular masses of the vacuolar membrane H+-ATPase in Saccharomyces cerevisiae under two kinetic conditions for ATP hydrolysis were measured by radiation inactivation. When vacuolar membrane vesicles were exposed to gamma-rays from 60Co, the activities catalyzing a single-cycle and multi-cycles of ATP hydrolysis both decreased as single-exponential functions of the radiation dosage. By applying the target theory, the functional molecular masses for single- and multi-cycle hydrolyses of ATP were determined to be approx. 0.9-1.1 X 10(5) and 4.1-5.3 X 10(5) Da, respectively. N,N'-Dicyclohexylcarbodiimide (DCCD) did not inhibit the former reaction but strongly inhibited the latter. It is suggested that the ATPase with a minimal composite of subunits a and b, in which subunit c is not necessarily involved operationally, can catalyze single-cycle hydrolysis of ATP, whereas for multi-cycle hydrolysis of ATP, the ATPase requires a properly organized oligomeric structure with subunits a-c, which may direct a positive cooperative mechanism of ATP hydrolysis and coupled H+ translocation in a DCCD-sensitive manner.
authors.affiliation: Department of Biology, Faculty of Science, University of Tokyo, Japan.
authors.forename: R
authors.initials: R
authors.lastname: Hirata
authors.forename: Y
authors.initials: Y
authors.lastname: Ohsumi
authors.forename: Y
authors.initials: Y
authors.lastname: Anraku
mesh_terms: D009327:4-Chloro-7-nitrobenzofurazan / Q000494:pharmacology; D004024:Dicyclohexylcarbodiimide / Q000494:pharmacology; D004307:Dose-Response Relationship, Radiation; D005720:Gamma Rays; D007425:Intracellular Membranes / Q000201:enzymology; D007700:Kinetics; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000528:radiation effects; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D014617:Vacuoles / Q000201:enzymology*
chemical_list: D004024:Dicyclohexylcarbodiimide; D006180:Proton-Translocating ATPases; D009327:4-Chloro-7-nitrobenzofurazan