Phosphorylation modulates the activity of glycine N-methyltransferase, a folate binding protein. In vitro phosphorylation is inhibited by the natural folate ligand.

Wagner C, Decha-Umphai W, Corbin J
J Biol Chem. 1989 264 (16): 9638-42

PMID: 2722853

Glycine N-methyltransferase (EC 2.1.1.20) was recently identified as a major folate binding protein of rat liver cytosol (Wagner, C., and Cook, R. J. (1984) Proc. Natl. Acad. Sci. U.S.A. 81, 3631-3634). Activity of the enzyme is inhibited when the natural folate ligand, 5-methyltetrahydropteroylpentaglutamate (5-CH3-H4PteGlu5), is bound. It has been suggested that glycine N-methyltransferase plays a role in regulating the availability of methyl groups in the liver. Purified transferase was phosphorylated in vitro by the catalytic subunit of cAMP-dependent protein kinase. If 5-CH3-H4PteGlu5 was first bound to the transferase, phosphorylation was inhibited. Phosphorylation of glycine N-methyltransferase in vitro increased its activity approximately 2-fold. 5-CH3-H4PteGlu5 inhibited the activity of newly phosphorylated enzyme as well as native enzyme. Freshly isolated rat hepatocytes incorporated 32P-labeled inorganic phosphate into this folate binding protein. Chemical analysis of purified enzyme showed about 0.55 mol of phosphate present per mol of glycine N-methyltransferase subunit. These results indicate that phosphorylation of glycine N-methyltransferase may provide a mechanism for modulating the activity of this enzyme and support its role in regulating the availability of methyl groups.

MeSH Terms (16)

Animals Carrier Proteins Enzyme Activation Folate Receptors, GPI-Anchored Folic Acid Glycine N-Methyltransferase Liver Male Methyltransferases Phosphates Phosphorylation Protein Kinases Rats Receptors, Cell Surface Substrate Specificity Tetrahydrofolates

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