Influence of copper on proton efflux from Saccharomyces cerevisiae and the protective effect of calcium and magnesium

The inhibitory effect of Cu on glucose-dependent H+ efflux from Saccharomyces cerevisiae was manifest at low (micromolar) concentrations, with the time period between the addition of glucose and commencement of H+ efflux, H+ efflux rate and duration all being affected with increasing Cu concentration (5-100 μM). Ca, at a concentration of 0.5 mM, completely removed the inhibitory effect of Cu at concentrations up to 50 μM and considerably reduced it at higher concentrations (up to 150 μM). Mg exhibited a similar but weaker protective effect against the influence of Cu. The protective effect of Ca against 50 μM Cu was evident at low Ca concentrations (2.5-5 μM), whereas Mg was effective at ≥50μM. In order to prevent the inhibitory effect of Cu, it was necessary to add Ca or Mg to the cell suspension before Cu addition. It is concluded that the protective effect of Ca and Mg is mediated by competitive and stabilizing interactions at the cell surface as well as physiological functions of Ca and Mg.