If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Locations of Mapped Genes:
Synonyms: S-adenosylmethionine biosynthesis
|Superclasses:||Biosynthesis → Cofactors, Prosthetic Groups, Electron Carriers Biosynthesis|
Pathway Summary from MetaCyc:
It has been said that no biological compound functions in as many different types of biological reactions as S-adenosyl-L-methionine (known as SAM or AdoMet). It is probably second only to ATP in the variety of reactions for which it serves as a cofactor. SAM is found in all living organisms, and fulfils three important roles:
* In transmethylation, SAM is the principal biological methyl donor.
* In transsulfuration, the sulfur atom of the SAM is converted via a series of enzymatic steps to cysteine, a precursor of taurine and glutathione, a major cellular anti-oxidant.
* In polyamine biosynthesis, SAM is the donor of aminopropyl groups.
The structure of SAM was first elucidated by Cantoni in 1951 [Cantoni51]. The key to SAM's activity lies in the presence of the high energy sulfonium ion, which activates each of the attached carbons toward nucleophilic attack. In most cases, SAM reacts by transfer of the S-methyl group to a long list of possible acceptors in transmethylation reactions.
SAM is synthesized in the cytosol of every cell from L-methionine and ATP, in a reaction catalyzed by methionine adenosyltransferase. In animals, up to half of the daily intake of L-methionine is converted to SAM. In this unusual reaction, the adenosyl moiety of ATP is transferred to methionine, forming a sulfonium ion which is a high energy reagent that can easily transfer its methyl group to a large variety of acceptor substrates including nucleic acids, proteins, phospholipids, biologic amines, and a long list of small molecules [Lu00a].
Superpathways: S-adenosyl-L-methionine cycle I
Pathway Evidence Glyph:
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