Illustrated Glossary of Organic Chemistry

S-adenosyl methionine (SAM): A cofactor whose molecular structure features an adenosine group bonded to the sulfur of methionine. A biological methylator.

	+				+
Methionine		ATP		S-adenosyl methionine (SAM)		Triphosphate

In the biosynthesis of S-adenosyl methionine, methionine (the nucleophile) displaces triphosphate (the leaving group) from ATP (the electrophile). This is an enzyme-mediated S_N2 reaction.

	SAM
Norepinephrine		Adrenaline

SAM's biochemical role is to transfer a methyl group to another molecule. In this example, SAM methylates norepinephrine to produce adrenaline.