Irreversible Inhibition of Biotin Transport in Yeast by Biotinyl- p -nitrophenyl Ester

Biotinyl-p-nitrophenyl ester (BNP), an active-ester derivative of biotin, irreversibly inactivates biotin transport in the yeast Saccharomyces cerevisiae. Transport inactivation is progressive with time and occurs at concentrations of the ester as low as 10(-7) M. In the presence of sodium azide, a reagent known to block biotin accumulation in yeast, the derivative is still effective. The specificity of inactivation by the ester is revealed by the following findings: (a) Biotinyl-p-nitroanilide and acetyl-p-nitrophenyl ester do not affect biotin transport; (b) the nitrophenyl ester does not affect the transport of lysine and aspartic acid, or that of L-sorbose; (c) inactivation of biotin transport by the ester is partially prevented when the cells are incubated with it in the presence of relatively high concentrations of biotin.