Modification of plasma membrane lipid order and H+-ATPase activity as partof the response of Saccharomyces cerevisiae to cultivation under mild and high copper stress

Plasma membrane lipid disorganization takes place in cells of Saccharomyces cerevisiae grown under copper stress, as shown by fluorescence anisotropy measurements with the lipid reporter probe 1,6-diphenyl-1,3,5-hexatriene. T he extent of plasma membrane disorganization, presumably due to copper-indu ced lipid peroxidation, was discontinuous when measured in cells sown in me dia supplemented with different concentrations of CuSO4. Results suggested the existence of adaptive mechanisms that cells employ to protect themselve s against the deleterious effects of copper. The adaptive mechanisms examin ed in this study included the coordinate increase in the activities of Cu,Z n-superoxide dismutase (up to five-fold), glutathione reductase (up to 1.7- fold): and plasma membrane H+-ATPase (up to threefold). These enzyme activi ties showed maximal levels in cells grown with copper supplied at intermedi ate concentrations, within the range that allowed growth. Significantly, at these concentrations, plasma membrane disorganization did not increase whe n increasing amounts of CuSO4 were supplied. However, at copper concentrati ons close to the maximal that allowed growth, the capacity of the yeast cel l response to cope with the deleterious effects of copper was exceeded; pla sma membrane lipid organization and plasma-membrane-bound H+-ATPase activit y drastically declined in response to the increased levels of copper stress and the consequences on growth kinetics were even more severe. Our results clearly suggest that modification of plasma membrane H+-ATPase activity is either part of or the result of the global response of yeast to mild or hi gh copper stress.