S-Adenosyl-L-homocysteine (SAH) is the biosynthetic precursor to homocysteine.

[1] SAH is formed by the demethylation of S-adenosyl-L-methionine.

[2][3] Adenosylhomocysteinase converts SAH into homocysteine and adenosine.

DNA methyltransferases are inhibited by SAH.

[4] Two S-adenosyl-L-homocysteine cofactor products can bind the active site of DNA methyltransferase 3B and prevent the DNA duplex from binding to the active site, which inhibits DNA methylation.