Anion Absorption by Baker's Yeast

Rates and equilibrium values of cation absorption by Baker's yeast, Saccharomyces cerevisiae, are in accord with a diffusion-limited exchange process which is independent of metabolic activity (7). At equilibrium the alkali ion content per unit volume of wet yeast exceeds the solution concentration by about 50fold in 10-3 M solution and about 800-fold at 10-5 M. Bromide anions in equilibrium with yeast fail to attain an apparent cellular concentration as great as that of the ambient solution. This is expected for a passive process of salt absorption. When ion binding is low, the amounts in cellular free space and adhering solution are predominant fractions of the total. Precautions are necessary to estimate or reduce the amount of these fractions in assessing possibly active or metabolically dependent absorption. Some results are reported here for absorption of bromide, phosphate, and sulfate by yeast, supplementing previous observations on bromide (7) and phosphate absorption (6).