Enzymatic cleavage of S-adenosylmethionine.

S-adenosylmethionine, known for some time to be the biological methyl donor in mammalian enzymatic transmethylation reactions (1,2), has more recently been implicated in other transalkylation reactions in bacteria and yeast (3-6). The enzyme system catalyzing the condensation of ATP and methionine to form AMe’ has been found in a variety of tissues and organisms, and has been purified from two sources and investigated in detail (7, 8). The broad distribution of these enzymes suggests that AMe likewise has widespread distribution and lends importance to a study of its further metabolism. The present paper reports the presence of an enzyme in baker’s yeast which decomposes AMe to 5’-methylthioadenosine and a-aminobutyrolactone (Equation 1; A = adenine, R = ribose) .