Mode of antifungal action of benanomicin A in Saccharomyces cerevisiae.

The mechanism of fungitoxic action of an antifungal antibiotic benanomicin A was studied with intact cells and protoplasts of Saccharomyces cerevisiae as well as with its enzymic preparations. The results obtained are summarized as follows: (1) benanomicin A at relatively high concentrations (almost equal to MIC) was fungicidal and disrupted the cell permeability barrier, inducing leakage of intracellular K+ and ATP in growing cells, while the antibiotic had none of these effects in non-growing cells; (2) no biosynthesis of any of several major cellular constituents in yeast cells was inhibited markedly or selectively enough to explain its fungitoxic activity; (3) whereas benanomicin A induced lysis of metabolically active yeast protoplasts incubated in the presence of glucose, inactive yeast protoplasts incubated without glucose were refractory to the lytic action of the antibiotic; (4) osmotically shocked yeast cells became feasible to the cidal action of benanomicin A; (5) benanomicin A substantially inhibited uptake of 6-deoxy-glucose by yeast cells; (6) liposomes composed of phospholipids and cholesterol were not susceptible to benanomicin A; and (7) benanomicin A inhibited in vitro activity of H(+)-ATPase from yeast cell membranes to a greater extent than that for H(+)-ATPase from yeast mitochondria or H(+)-ATPase from yeast vacuolar membranes. Based on these and our previous data that benanomicin A preferentially binds to mannan or mannoproteins constituting the cell wall and cell membrane of yeasts, such binding of the antibiotic is suggested to deteriorate the normal structure and function of those cell membranes of yeasts which are in a growing or metabolically active state, ultimately leading to cell death.