Photoinactivation of the thiamine transport system in Saccharomyces cerevisiae with 4-azido-2-nitrobenzoylthiamine.

A newly synthesized photoreactive thiamine derivative, 4-azido-2-nitrobenzoylthiamine was found to be a competitive inhibitor of the thiamine transport system in Saccharomyces cerevisiae, exhibiting an apparent Ki of 36 nM. When exposed to visible light, 4-azido-2-nitrobenzoylthiamine irreversibly inactivated the thiamine transport. 4-Azido-2-nitrobenzoylthiamine-dependent photoinactivation of thiamine transport was partially protected by thiamine, but not by the nitrene-trapping reagent p-aminobenzoate. On the other hand, the irradiation of the yeast cells in the presence of 4-azido-2-nitrobenzoylthiamine did not significantly lead to inactivation of the biotin transport system. The results suggest that 4-azido-2-nitrobenzoylthiamine is a specific irreversible inhibitor of the thiamine transport system in Saccharomyces cerevisiae.