Effects of different salts on the plasma membrane ATPase and on proton transport in yeast

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Abstract
The effect of various inorganic and organic salts on the plasma membrane ATPase from the yeast Saccharomyces cerevisiae and on its proton transport were studied. We observed up to 460% stimulation of ATPase activity depending on the type of salt. The anion had a major effect and the monovalent cation a minor effect. These activations were the consequence of an increase in the affinity of the ATPase for activating Mg2+ ions and of an enhancement of Vmax. The mechanism of the reaction between enzyme, substrate, and Mg2+ ions was not altered by these salts. Similary, several salts stimulated the proton transport through the plasma membranes of Saccharomyces cerevisiae as evidenced by fluorescence quench of the dye 9-amino-6-chloro-2-methoxyacridine in plasma membrane vesicles. It is proposed that this effect is due to a stimulation of ATPase activity and in addition to charge compensation by membrane permeating anions.