Phosphorylation modulates the activity of glycine N-methyltransferase, a folate binding protein. In vitro phosphorylation is inhibited by the natural folate ligand.
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.
Wagner
C
C
Department of Biochemistry, Vanderbilt University, Nashville, Tennessee.
Decha-Umphai
W
W
Corbin
J
J
D000818:Animals; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D058973:Folate Receptors, GPI-Anchored; D005492:Folic Acid / Q000378:metabolism / Q000502:physiology*; D050938:Glycine N-Methyltransferase; D008099:Liver / Q000201:enzymology; D008297:Male; D008780:Methyltransferases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010710:Phosphates / Q000032:analysis; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D051381:Rats; D011956:Receptors, Cell Surface; D013379:Substrate Specificity; D013763:Tetrahydrofolates / Q000494:pharmacology
D002352:Carrier Proteins; D058973:Folate Receptors, GPI-Anchored; D010710:Phosphates; D011956:Receptors, Cell Surface; D013763:Tetrahydrofolates; D005492:Folic Acid; D008780:Methyltransferases; D050938:Glycine N-Methyltransferase; C494512:Gnmt protein, rat; D011494:Protein Kinases; C005984:5-methyltetrahydrofolate