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S-Adenosylmethionine (SAM)
Universal biological methyl donor formed from methionine and ATP that donates its methyl group in over 100 methyltransferase reactions, becoming S-adenosylhomocysteine (SAH).
Also: AdoMet, SAM, SAMe
The SAM:SAH ratio (methylation potential) regulates DNA, histone, phospholipid, and small-molecule methylation. SAM is regenerated from homocysteine via the methionine synthase reaction (requires 5-methyl-THF and B12) or, in liver and kidney, via betaine-homocysteine methyltransferase using betaine derived from choline. Disruption of SAM availability links folate/B12/choline status to epigenetic programming.
How one textbook covers it
Modern Nutrition in Health and Disease, 12th ed. — Ch 26: Folate
The SAM:SAH ratio (methylation potential) regulates DNA, histone, phospholipid, and small-molecule methylation. SAM is regenerated from homocysteine via the methionine synthase reaction (requires 5-methyl-THF and B12) or, in liver and kidney, via betaine-homocysteine methyltransferase using betaine derived from choline. Disruption of SAM availability links folate/B12/choline status to epigenetic programming.
Related terms
Choline, DNA methylation, Homocysteine, One-carbon metabolism