Zinc uptake and toxicity in the yeasts Sporobolomyces roseus and Saccharomyces cerevisiae

Sporobolomyces roseus and Saccharomyces cerevisiae accumulated zinc from zinc-containing medium. Uptake was biphasic and consisted of an initial, rapid, metabolism-independent binding of zinc to cell surfaces which was followed by slower, metabolism-dependent intracellular uptake of zinc. Spor. roseus could bind approximately eight times more zinc, per unit surface area, than could S. cerevisiae. Metabolism-dependent zinc uptake followed Michaelis-Menten kinetics with K(m) values of 0.09 and 5.00 mM-Zn2+ for Spor. roseus and S. cerevisiae, respectively; corresponding V(max) values were 0.51 and 9.09 nmol Zn2+ (mg dry wt)-1 min-1. Zinc uptake by viable cells was not accompanied by potassium release in either yeast, but zinc levels which affected viability in S. cerevisiae caused this yeast to release K+. No efflux of K+ was observed for Spor. roseus despite its greater sensitivity to zinc.