The mechanism of utilization of thiomethyladenosine in the biosynthesis of methionine.

A variety of methyl donor compounds, such as choline and betaine, are known to be sources of the methyl group of methionine when this compound is synthesized by animal tissues (du Vigneaud, 1952). However, none of the known transmethylation reactions has been shown to occur in the bacterial synthesis of methionine. In the first paper in this series (Shapiro, 1953) it was shown that thiomethyladenosine could support the growth of certain methionine auxotrophs of Aerobacer aerogenes. The mechanism of utilization of thiomethyladenosine by one of these mutants has been investigated further. The results to be presented here suggest a new pathway of biosynthesis of methionine by this organism and indicate that thiomethyladenosine is a precursor of the thiomethyl group of methionine.