Ionophores and intact cells I. Valinomycin and nigericin act preferentially on mitochondria and not on the plasma membrane of Saccharomyces cerevisiae

Valinomycin and nigericin prevented growth of 13 strains of the yeast Saccharomyces cerevisiae on non-fermentable substrate glycerol without affecting much fermentative growth on glucose. The two antibiotics did not induce swelling and lysis of yeast protoplasts in potassium acetate and did not modify uptake and release of Rb⁺ by the yeast cells. Both antibiotics were taken up by yeast cells at a relatively low rate. Nigericin accelerated the glucose-induced changes of fluorescence of a cyanine dye absorbed by yeast cells, which had been previously ascribed to a depolarization-repolarization cycle of the mitochondrial membrane. The data suggest that valinomycin and nigericin act as ionophores in the inner mitochondrial membrane and not in the plasma membrane of intact yeast cells.