= S-adenosylmethionine
{c}
<S-adenosylmethionine> is an activated <methionine> derivative in which an adenosyl group is bonded to the <sulfur> atom. The positively charged <sulfur> bears a transferable <methyl group>; <S-adenosylmethionine> therefore couples cellular <metabolism> to transfer of <methyl groups> onto other <molecules>, including <DNA> and <proteins>.<PubChem Compound database by National Center for Biotechnology Information>[S-adenosylmethionine records CID34755 and parent CID34756; structure, charge conventions and methyl-donor role]{ref}
The same starting <molecule> can also enter a different reaction. <1-aminocyclopropane-1-carboxylate synthase> converts <S-adenosylmethionine> into <1-aminocyclopropane-1-carboxylate> and <methylthioadenosine>, on the route to <plant> <Ethylene>. Here the <enzyme> directs fragmentation and ring formation rather than simple <methyl group> transfer. Naming a common substrate does not by itself identify which reaction occurred.<Ethylene biosynthesis: Identification of 1-aminocyclopropane-1-carboxylic acid as an intermediate in the conversion of methionine to ethylene by D. O. Adams and S. F. Yang>[Abstract; methionine-to-ethylene pathway and proposed fragmentation]{ref}
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