Guanidinoacetate N-methyltransferase

Guanidinoacetate N-methyltransferase (EC 2.1.1.2) is an enzyme that is encoded by gene GAMT located on chromosome 19p13.3^[5][6] and catalyzes the chemical reaction:

This is a methylation reaction in which glycocyamine is converted to creatine. The methyl group comes from the cofactor, S-adenosyl methionine (SAM), which loses its methyl group and becomes S-adenosyl-L-homocysteine (SAH).^[7][8]

This enzyme belongs to the family of transferases, specifically those transferring one-carbon group methyltransferases. The systematic name of this enzyme class is S-adenosyl-L-methionine:N-guanidinoacetate methyltransferase. Other names in common use include GA methylpherase, guanidinoacetate methyltransferase, guanidinoacetate transmethylase, methionine-guanidinoacetic transmethylase, and guanidoacetate methyltransferase. It participates in the metabolism of amino acids.^[9]

Defects in the gene which encodes this protein have been implicated in neurologic syndromes and muscular hypotonia, probably due to creatine deficiency and accumulation of guanidinoacetate in the brain of affected individuals.^[10] Two transcript variants encoding different isoforms have been described for this gene.^[11]