Ahhreriarions: DDG, 2-deoxy-~-glucose ; NTA, nitrilotriacetic acid.

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 , values of 0.09 and 5-00 mM-Zn2+ for Spor. roseus and S . cerevisiae, respectively; corresponding V,,, values were 0-5 1 and 9.09 nmol Zn2+ (mg dry wt)-l min-'. 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.

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SynopsisThe analysis of K + release, respiration rates and tests relying on diffusion processes in agar medium have applications for the study and assessment of heavy metal toxicity towards fungi and yeasts. Such techniques have been seldom exploited for this purpose but can provide information not only on toxicity but also on morphological and physiological responses towards heavy metals.

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