post translational modification methylation

<a href="http://www.creative-proteomics.com/services/Methylation.htm">post translational modification methylation</a> is mediated by methyltransferases, and S-adenosyl methionine (SAM) is the primary methyl group donor. Methylation occurs so often that SAM has been suggested to be the most-used substrate in enzymatic reactions afterATP. Additionally, while N-methylation is irreversible, O-methylation is potentially reversible.