Regulation of cellular Mg 2+ by Saccharomyces cerevisiae

Abstract

Regulation of cellular Mg 2+ by S. cerevisiae was investigated. The minimal concentration of Mg 2+ that results in optimal growth of S. cerevisiae is about 30 μM and a half-maximum growth rate is attained at about 5 μM Mg 2+. Since the plasma membrane has an electrical potential greater than 100 mV, passive equilibration of Mg 2+ across the plasma membrane would provide sufficient cytosolic Mg 2+ (0.1–1 mM). The total cellular Mg 2+ of cells grown in synthetic medium containing 1 mM Mg 2+ is about 400 nmol/mg protein, most of which is bound to polyphosphate, nucleic acids, and ATP. Total cellular Mg 2+ decreases to about 80 nmol/mg protein as the Mg 2+ in synthetic growth medium is reduced to 0.02 mM, but remains relatively constant in growth medium containing 1 to 100 mM Mg 2+. Cells shifted into Mg 2+-free medium continue to grow by utilizing the vacuolar Mg 2+ stores. Mg 2+-starved cells replenish vacuolar Mg 2+ stores with a halftime of 30 min. following the addition of 1 mM Mg 2+ to the growth medium. The data indicate that cytosolic Mg 2+ is maintained by the regulation of Mg 2+ fluxes across both the vacuolar and plasma membranes.