Abstract
The occurrence of thiamine-binding proteins in animal, plant and microbial sources has been known in recent years. We found two thiamine-binding proteins in Saccharomyces cerevisiae. A soluble thiamine-binding proteins present in the periplasm appeared to be a glycoprotein with a molecular weight of 140,000, while a membrane-bound thiamine-binding protein was found to be located in the cytoplasmic membrane of yeast cells. Some properties of these yeast thiamine-binding proteins are described. On the other hand, a thiamine-binding protein purified from rice bran was presumed to be composed of two identical subunits with a molecular weight of 50,000 which was not a glycoprotein. From the results obtained by chemical modification of these thiamine-binding proteins it was suggested that an ionic interaction between a carboxyl residue in the protein and a quaternary nitrogen atom of thiazole moiety of thiamine molecule plays a role in the binding of the thiamine-binding protein to thiamine.
