Partial characterization of the plasma membrane ATPase from arho 0 petite strain ofSaccharomyces cerevisiae

Crude membrane preparations of arho ⁰ mutant ofSaccharomyces cerevisiae exhibit Mg²⁺-dependent ATPase activity. Over the optimal pH range, 5.0–6.75, the apparentV _max of the enzyme equals 590 nmoles of ATP hydrolyzed per minute per milligram protein, with an apparentK _m for ATP of 1.3 mM. ATP hydrolysis is insensitive to ouabain, venturicidin, aurovertin, and the protein inhibitor described by Pullman and Monroy; inhibited by oligomycin (at high concentrations) and sodium orthovandate, and it is sensitive to dicyclohexylcarbodiimide,p-hydroxymercuribenzoate, hydroxylamine, sodium fluoride, and sodium iodoacetate. The pH optimum and the inhibitor pattern distinguish the plasma membrane enzyme from the mitochondrial F₁ ATPase still present in these cells (this activity is sensitive to efrapeptin, aurovertin, and the protein inhibitor, but resistant to DCCD). In addition, the activity of the plasma membrane enzyme and its affinity for ATP are responsive to changes in the composition of the growth medium, with the highest activity observed in cells grown on methyl--d-glucoside, a sugar which results not only in partial release from catabolite repression but also requires the induction of an active transport system for growth.Author to whom correspondence should be addressed; recipient of a Research Career Award No. K06 05060 from the Institute of General Medical Sciences.