Cadmium‐uptake and influence on plasma membrane functions of yeast†

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Abstract
115mCd2+‐uptake and accumulation by the yeast Saccharomyces cerevisiae was rapid and largely dependent on the presence of glucose. From the time response after addition of glucose and from studies with energy poisons or with cycloheximide, it could be deduced that the observed effects were neither due to a cotransport system of glucose and Cd2+ nor due to the biosynthesis of binding or transport proteins, but to an energy‐dependent transport system (Km:0.3 mM, Vm ax:5n mol/min x mg dry wt), being driven by the electrochemical potential across the plasma membrane. There was a good correlation between the influence of cadmium on the kinetics of cell growth and toxic effects of Cd2+ on the plasma membrane H+‐ATPase. This inhibition was strongly dependent on the experimental conditions. Cadmium ions were most effective at high pH and high magnesium concentrations. They enhanced Km , whereas Vmax was not affected significantly. Under favourable conditions we found a lowest effective concentration of Cd2+ at <1μM and 50% inhibition at 3.5 μm. In contrast, CdCl2 had no effect on glucose and purine transport systems.

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