almost all cellular methylation reactions. GNMT is therefore likely to regulate cellular methylation capacity. An endogenous ligand of GNMT, 5-methyltetrahydropteroylpentaglutamate (5-CH3-H4PteGIu5) is a powerful inhibitor of this enzyme. Thus, GNMT has been proposed to link the de novo synthesis of methyl groups to the ratio of SAM to SAH, which in turn serves as a bridge between methionine and one-carbon metabolism. In addition to the methyltransferase activity, the 4S polycyclic aromatic hydrocarbon (PAH)-binding protein and GNMT are one and the same protein. The catalytic site resembles a molecular basket, unlike most other SAM-dependent methyltransferases, which therefore suggests that GNMT may be capable of capturing unidentified chemicals as a part of a detoxification process. Therefore, GNMT has been proposed to be a protein with diverse functionality. Clinical significance GNMT has been shown to detoxify some environmental carcinogens such as polyaromatic hydrocarbons and aflatoxin. There is mounting evidence that supports the involvement of GNMT deficiency in liver carcinogenesis. Inducer The glycoside natural product 1,2,3,4,6-penta-O-galloyl-β-d-glucopyranoside (PGG) isolated from Paeonia lactiflora, an Asian flower plant, induces GNMT mRNA and protein expression in Huh7 human hepatoma cells. References Further reading