title: Radiation-inactivation analysis of vacuolar H(+)-ATPase and H(+)-pyrophosphatase from Beta vulgaris L. Functional sizes for substrate hydrolysis and for H+ transport.
abstract: The functional sizes of the vacuolar H(+)-ATPase (V-ATPase; EC 3.6.1.34) and H(+)-pyrophosphatase (PPase; EC 3.6.1.1) from vacuolar membranes of red beet (Beta vulgaris L.) were estimated by radiation inactivation, both for substrate hydrolysis and for H+ transport. For the V-ATPase, the radiation-inactivation size for H+ transport was 446 (403-497) kDa and that for ATP hydrolysis was 394 (359-435) kDa. The low values of both of these estimates suggest that not all subunits which may co-purify with V-ATPases are required for either hydrolysis or transport. For the PPase, the radiation-inactivation size for hydrolysis was 91 (82-103) kDa, suggesting that the minimum functional unit for hydrolysis is the 81 kDa monomer. In contrast to the V-ATPase, the PPase gave a radiation-inactivation size for transport which was 3-4-fold larger than that for hydrolysis (two estimates for transport gave 307 and 350 kDa), indicating that a single catalytic subunit is insufficient for transport activity.
authors.affiliation: Department of Biology, McGill University, Montréal, Québec, Canada.
authors.forename: V
authors.initials: V
authors.lastname: Sarafian
authors.forename: M
authors.initials: M
authors.lastname: Potier
authors.forename: R J
authors.initials: RJ
authors.lastname: Poole
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D004307:Dose-Response Relationship, Radiation; D005720:Gamma Rays; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D043564:Inorganic Pyrophosphatase; D007425:Intracellular Membranes / Q000201:enzymology; D007700:Kinetics; D046911:Macromolecular Substances; D010944:Plants / Q000201:enzymology*; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors / Q000528:radiation effects*; D011755:Pyrophosphatases / Q000037:antagonists & inhibitors / Q000528:radiation effects*; D014617:Vacuoles / Q000201:enzymology*
chemical_list: D046911:Macromolecular Substances; D000255:Adenosine Triphosphate; D011755:Pyrophosphatases; D043564:Inorganic Pyrophosphatase; D006180:Proton-Translocating ATPases