Abstract
A thiamine-binding protein was purified from the extract of rice bran acetone powder by conventional procedures of acid precipitation, a series of column chromatography on DEAE-Sephadex A-50 and DEAE-cellulose, and gel filtration of Sephadex G-200. The purified thiamine-binding protein was nearly homogeneous as judged by disc gel electrophoresis and the molecular weight was estimated to be 94, 000 by gel filtration on Sephadex G-200 and 50, 000 by sodium dodecylsulfate (SDS) gel electrophoresis, suggesting that the protein is composed of two identical subunits. The apparent Kd and Bmax of the binding for [14C]thiamine was 0.44±0.05 μM and 17.2±0.7 nmol/mg of protein, respectively. The optimal pH for the binding is between 8.0 and 9.0. From the competition experiment using several thiamine derivatives, high binding specificity of the protein for thiamine was presumed.
