Purification and Characterization of Glycine N-Methyltransferase

Glycine N-methyltransferase, an enzyme which methylates glycine in the N-position to yield sarcosine, has been purified to homogeneity from rabbit liver and partially characterized. The enzyme has a molecular weight of 123,500 as determined by sedimentation equilibrium centrifugation and consists of 3 to 4 nonidentical subunits with molecular weights in the range of 27,000 to 33,000 as determined by mobility in sodium dodecyl sulfate polyacrylamide gels. The apparent Michaelis constants for glycine and S-adenosylmethionine are 2.2 and 0.1 mm, respectively. The enzyme has a high percentage of aromatic amino acids, conferring a hydrophobic character upon it. It also contains carbohydrate in the form of sialic acid, 4 residues per mole of protein, and hexose, 2 residues per mole of protein, as well as 12 acetyl groups per mole of protein.