Abstract
In Saccharomyces cerevisiae, genetic and biochemical analyses have revealed the existence of two species of acid phosphatase; one, repressible by Pi and the other, repressible by thiamin. the properties of thiamin-repressible acid phosphatase (T-rAPase) encoded by PHO 3 gene in S. cerevisiae were investigated, since the fact that the PHO 3 product is repressible by thiamin may indicate a possible role for the enzyme in thiamin matabolism. As a result, T-rAPase was proved to be identical to a periplasmic soluble thiamin-binding protein biochemically and genetically. The pho 3 mutant cells of S. cerevisiae in contrast to the parent cells have markedly reduced activity of the uptake of [^<14>C]thiamin phosphates. From these results with the enzymatic properties obtained, it was concluded that thiamin repressible acid phosphatase in s. cerevisiae physiologically catalyzes the hydrolysis of thiamin phosphates in the periplasmic space, thus participating in utilization of the thiamin moiety of the phosphates by yeast cells. Moreover, evidences obtained from the modification of T-rAPase with 1-ethyl-3-(3-dimethyl-aminopropyl) carbodiimide indicated that the high affinity of T-rAPase for thiamin phosphates is due to the thiamin-binding properties of this enzyme.
