Abstract
Uptake rates of benzoic and propanoic acid into Zygosaccharomyces bailii were proportional to the concentration of undissociated acid and showed no indication of limitation at high concentrations. Benzoic acid permeated 27 times faster than propanoic acid. Other low-M r fatty acids were taken up at rates approximately related to their lipophilicity. Glucose stimulated uptake rate and inhibitors of glucose transport or metabolism removed the stimulation. It was concluded that the principal mechanism of uptake was diffusion of undissociated acid. The Z. bailii membrane had lower permeabilities than reported for other cell types and lipid bilayers. Growth in the presence of benzoic acid reduced permeability to benzoic acid further. Preservative-resistant yeast species had lower uptake rates of propanoic acid than sensitive ones. Degradation of the cell wall did not change the permeability to propanoic acid.
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