Enzymatic properties of the PMA2 plasma membrane-bound H(+)-ATPase of Saccharomyces cerevisiae.

The PMA1 H(+)-ATPase can be functionally replaced by its isoform PMA2 in the plasma membrane from Saccharomyces cerevisiae (Supply, P., Wach, A., Thinès-Sempoux, D., and Goffeau, A. (1993) J. Biol. Chem. 268, 19744-19752). From strains expressing either only PMA1 or PMA2, plasma membranes were isolated and their ATPase activities compared. Despite their 89% identity, the two enzymes differ as to the following parameters: activation by glucose and by Triton X-100, pH optimum, requirement for divalent cations, and inhibition by vanadate and by erythrosin B. More striking, the glucose-activated PMA2 enzyme displays a three to four times higher apparent affinity for MgATP, and maximal activity is reached with a 10-fold lower free Mg2+ concentration. These results suggest that the difference in PMA1 and PMA2 expression level is correlated with different H(+)-ATPase functions. The analysis of the PMA1 and PMA2 sequence alignment, compared with reported PMA1 mutations, points to a few residue substitutions as putative contributors to the observed kinetic changes.