Comparative effects of Saccharomyces cerevisiae cultivation under copper stress on the activity and kinetic parameters of plasma-membrane-bound H+-ATPases PMA1 and PMA2
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The major yeast plasma membrane H+-ATPase is encoded by the essential PMA1 gene. The PMA2 gene encodes an H+-ATPase that is functionally interchangeable with the one encoded by PMA1, but it is expressed at a much lower level than the PMA1 gene and it is not essential. Using genetically manipulated strains of Saccharomyces cerevisiae that exclusively synthesize PMA1 ATPase or PMA2 ATPase under control of the PMA1 promoter, we found that yeast cultivation under mild copper stress leads to a similar activation of PMA2 and PMA1 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 PMA2 ATPase than for PMA1 ATPase. The higher tolerance to high copper stress of the artificial strain synthesizing PMA2 ATPase exclusively, as compared to that synthesizing solely PMA1 ATPase, correlated both with the lower sensitivity of PMA2 ATPase to the deleterious effects of copper in vivo and with its higher apparent affinity for MgATP, and suggests that plasma membrane H+-ATPase activity plays a role in yeast tolerance to copper.
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