title: The H subunit (Vma13p) of the yeast V-ATPase inhibits the ATPase activity of cytosolic V1 complexes.
abstract: V-ATPases are composed of a peripheral complex containing the ATP-binding sites, the V(1) sector, attached to a membrane complex containing the proton pore, the V(o) sector. In vivo, free, inactive V(1) and V(o) sectors exist in dynamic equilibrium with fully assembled, active V(1) V(o) complexes, and this equilibrium can be perturbed by changes in carbon source. Free V(1) complexes were isolated from the cytosol of wild-type yeast cells and mutant strains lacking V(o) subunit c (Vma3p) or V(1) subunit H (Vma13p). V(1) complexes from wild-type or vma3Delta mutant cells were very similar, and contained all previously identified yeast V(1) subunits except subunit C (Vma5p). These V(1) complexes hydrolyzed CaATP but not MgATP, and CaATP hydrolysis rapidly decelerated with time. V(1) complexes from vma13Delta cells contained all V(1) subunits except C and H, and had markedly different catalytic properties. The initial rate of CaATP hydrolysis was maintained for much longer. The complexes also hydrolyzed MgATP, but showed a rapid deceleration in hydrolysis. These results indicate that the H subunit plays an important role in silencing unproductive ATP hydrolysis by cytosolic V(1) complexes, but suggest that other mechanisms, such as product inhibition, may also play a role in silencing in vivo.
authors.affiliation: Department of Biochemistry and Molecular Biology, SUNY Upstate Medical University, Syracuse, New York 13210, USA.
authors.forename: K J
authors.initials: KJ
authors.lastname: Parra
authors.forename: K L
authors.initials: KL
authors.lastname: Keenan
authors.forename: P M
authors.initials: PM
authors.lastname: Kane
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D001665:Binding Sites; D017301:Ca(2+) Mg(2+)-ATPase / Q000737:chemistry / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000737:chemistry / Q000378:metabolism*; D003001:Cloning, Molecular; D003600:Cytosol / Q000201:enzymology; D017353:Gene Deletion; D007700:Kinetics; D046911:Macromolecular Substances; D017494:Proton Pumps / Q000737:chemistry / Q000378:metabolism; D006180:Proton-Translocating ATPases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics; D025262:Vacuolar Proton-Translocating ATPases
chemical_list: D046911:Macromolecular Substances; D017494:Proton Pumps; D011994:Recombinant Proteins; D000255:Adenosine Triphosphate; D017301:Ca(2+) Mg(2+)-ATPase; D025262:Vacuolar Proton-Translocating ATPases; D006180:Proton-Translocating ATPases; D000252:Calcium-Transporting ATPases