Figure 10 Structure of the cofactor Sadenosyl Lmethionine 22 SAM generic reactions of O and Smethylation a and of Nmethylation b

Methyltransferases involved in xenobiotic metabolism include:

• the main enzyme responsible for O-methylation, namely catechol O-methyltransferase (EC 2.1.1.6; COMT), which is mainly cytosolic but also exists in membrane-bound form;

• various enzymes involved in N-methylation and characterized by different substrate specificities, e.g., nicotinamide N-methyltransferase (EC 2.1.1.1), histamine N-methyltransferase (EC 2.1.1.8), phenylethanolamine N-methyl-transferase (EC 2.1.1.28), and a nonspecific arylamine N-methyltransferase (EC 2.1.1.49); and

• enzymes catalyzing S-methylation, namely the membrane-bound thiol methyltransferase (EC 2.1.1.9) and the cytosolic thiopurine methyltransferase (EC 2.1.1.67).

This classification makes explicit the three types of functionalities undergoing biomethylation, namely hydroxy (phenolic), amino, and thiol groups.

Was this article helpful?

0 0

Post a comment