Studies on the mechanism of the antifungal action of benzoate

Abstract

A method is described for the determination of the pH of intracellular H2O based on the distribution of [14C]benzoate (0.01 mM) between intra- and extra-cellular H2O. Benzoate at higher concentrations (2-10 mM) entered the yeast [Saccharomyces cerevisiae] cell in the undissociated form; its neutralization within the cell caused a shift of the pH of the intracellular H2O by > 1 pH units. Benzoate caused an accumulation of the 2 hexose monophosphates of yeast glucose fermentation and a decrease in intermediates beyond phosphofructokinase, suggesting inhibition at this stage. Benzoate also caused a concomitant fall in ATP. Phosphofructokinase was inhibited to a greater extent than hexokinase at acid pH. There was a relationship between intracellular pH, phosphofructokinase inhibition and CO2 production, suggesting that the antifungal action of benzoate is caused by an accumulation of benzoate at low external pH, which lowers the intracellular pH into the range where phosphofructokinase is sensitive. The subsequent inhibition of gycolysis caused a fall in ATP and thus restricts growth. These results are relevant to the use of benzoate as a food or pharmaceutical preservative.