Biosynthesis of high specific activity L-35S-methionine by using a diploid yeast-saccharomyces cerevisiae

Biosynthesis of L-35S-methionine was made on a commercial scale by using the diploid strain of baker's yeast-Saccharomyces cerevisiae X2180. Yeast cells were grown in a sulphur-depleted synthetic medium in which Na235SO4 (50 mCi/mL) was supplemented as the sole sulphur source. After acid hydrolysis, the 35S-labelled protein hydrolysate was subjected to paper and column chromatographic separations to get the individual L-35S-aminoacids. The radiochemical yields of methionine and cysteine were 18-20% and 5.5-7.0% respectively. The radiochemical purity of the pure products obtained was > 95%. The specific activity of L-35S-methionine was as high as 400 Ci/m mole when Na235SO4 of specific activity in the range of 440 - 525 Ci/m mole was used as the starting material for the growth of the yeast cells. (author). 4 refs., 1 tab