Reversibility of the affinity labelled-biotin transport system in yeast cells

Transport of biotin by Saccharomyces cerevisiae is inhibited by biotynyl p-nitrophenyl ester. Conversion of the inhibited cells to spheroplasts or simple treatment with thiols results in a total restoration of vitamin transport. Biotynyl p-nitrophenyl ester-induced inhibition is not due to an intracellular accumulation of the vitamin and consequent regulation, but appears to be due to specific labelling of the transport system.