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. Author manuscript; available in PMC: 2010 Jul 15.
Published in final edited form as: Free Radic Biol Med. 2009 Apr 10;47(2):115–127. doi: 10.1016/j.freeradbiomed.2009.04.010

Fig. 4. Enzymatic mechanism of DNA methyltransferases (DNMTs).

Fig. 4

Methylation of cytosine begins with the nucleophillic attack of position 6 by a thiolate nucleophile. The resulting electron rich region at position 5 is then at attacked by the methyl group of Sadenosylmethionine (SAM). The reaction then proceeds with the removal of the hydrogen at position 5 by a basic amino acid in the active site of DNMT. In the final step, the double bond is reformed in the pyrimidine ring, resulting in elimination of bond between position 6 and the DNMT.