Comparative effects of Saccharomyces cerevisiae cultivation under copper stress on the activity and kinetic parameters of plasma-membrane-bound H+-ATPases PMA(1) and PMA(2)

The major yeast plasma membrane H+-ATPase is encoded by the essential PMA(1 ) gene. The PMA(2) gene encodes an H+-ATPase that is functionally interchan geable with the one encoded by PMA(1), but it is expressed at a much lower level than the PMA(1) gene and it is not essential. Using genetically manip ulated strains of Saccharomyces cerevisiae that exclusively synthesize PMA( 1) ATPase or PMA(2) ATPase under control of the PMA(1) promoter, we found t hat yeast cultivation under mild copper stress leads to a similar activatio n of PMA(2) and PMA(1) isoforms. At high inhibitory copper concentrations ( close to the maximum that allowed growth), ATPase activity was reduced from maximal levels; this decrease in activity was less important for PMA(2) AT Pase than for PMA(1) ATPase. The higher tolerance to high copper stress of the artificial strain synthesizing PMA(2) ATPase exclusively, as compared t o that synthesizing solely PMA(1) ATPase, correlated both with the lower se nsitivity of PMA(2) ATPase to the deleterious effects of copper in vivo and with its higher apparent affinity for MgATP, and suggests that plasma memb rane H+-ATPase activity plays a role in yeast tolerance to copper.