The radiopurity of S‐adenosylmethionine and S‐adenosylethionine preparations

In the biosynthesis of labeled S‐adenosylmethionine and S‐adeno‐sylethionine from the corresponding 14C‐labeled sulfur amino acids by yeast, some radioimpurity occurred by non‐specific labeling of the sulfonium compounds. This is explained by partial degradation of methionine and ethionine in the yeast cells, followed by utilization of the randomized fragments in the biosynthesis. The degree of mislabeling remains low because endogenous methionine synthesis from metabolic pool constituents is suppressed by the excess of methionine and ethionine supplement in the culture medium. Hydrolysis of the sulfonium compounds and analysis of the fragments showed that the misplaced isotope amounts to approximately 0.5% in the adenine, and 0.2% in the homoserine part compared with the total radioactivity of the sulfonium compounds (100%).