Molecular and biochemical characterization of the Dio-9-resistant pma1-1 mutation of the H(+)-ATPase from Saccharomyces cerevisiae

The plasma-membrane H(+)-ATPase gene PMA1 was sequenced in four Dio-9-resistant strains of Saccharomyces cerevisiae, isolated independently. The same amino acid substitution Ala608----Thr was found in the four mutated strains. The mutant ATPase activity was decreased while the Km value for MgATP was increased. The ATPase efficiency (V/Km) of the mutant was reduced by a factor of 25 under acid conditions (pH 5.5), and by a factor of 10 at physiological pH (pH 6.6). The mutation also strongly reduces the inhibition by vanadate of ATPase activity, suggesting that the altered amino acid is involved in phosphate binding and/or in the E1-E2 transition.