Cation (K+, Mg2+, Ca2+) exchange in Pb2+ accumulation by Saccharomyces cerevisiae

The relationship between Pb2+ accumulation and cation (K+, Mg2+, Ca2+) release in Saccharomyces cerevisiae was extensively investigated. As Pb2+ accumulation proceeded, the release of cellular metal ions such as K+, Mg2+ and Ca2+ was concomitantly released within 24 h, thereafter Pb2+ penetrated into the inner cellular parts and consequently plasmolysis of the cell was observed by TEM analysis. Pb2+ accumulation process in S. cerevisiae after 24 h was metabolism-independent because of the absence of cell viability. As the cell storage time was prolonged, the released amount of K+ was markedly increased, while the amount of accumulated Pb2+ was nearly constant regardless of cell storage time and the time required to reach an equilibrium state was shortened. The autoclaved cells had less Pb2+ accumulation capacity than the untreated cells, and the amounts of released K+ and Mg2+ were very low due to the denaturation of cell surface and cell membrane.