Activation of the H+-ATPase in the plasma membrane of cells of Saccharomyces cerevisiae grown under mild copper stress

Cells of Saccharomyces cerevisiae exhibited a more active plasma membrane H +-ATPase during growth in media supplemented with CuSO4 concentrations equa l to or below 1 mM than did cells cultivated in the absence of copper stres s. Maximal specific activities were found with 0.5 mM CuSO4. ATPase activit y declined when cells were grown with higher concentrations up to 1.5 mM (t he maximal concentration that allowed growth), probably due to severe disor ganization of plasma membrane . Cu2+-induced maximal activation was reflect ed in an increase of V-max (approximately threefold) and in the slight decr ease of the K-m for MgATP (from 0.93 +/- 0.13 to 0.65 +/- 0.16 mM). The exp ression of the gene encoding the essential plasma membrane ATPase (PMA1) wa s reduced with a dose-dependent pattern in cells grown with inhibitory conc entrations of copper, while the weakly expressed PMA2 gene promoter was mod erately more efficient in cells cultivated under mild copper stress (1.5-fo ld maximal activation). ATPase was activated by copper despite the slightly lower content of ATPase protein in the plasma membrane of Cu2+-grown cells and the powerful inhibitory effect of Cu2+ in vitro.