Purification and Properties of Protein Methylase II

Abstract

Abstract An enzyme, methylase II, has been purified approximately 900-fold from calf thymus cytosol. The enzyme methylates exogenously added proteins with S-adenosyl-l-methionine-methyl-14C. Among the proteins tested, a protein isolated from calf thymus serves the best as methyl acceptor. The purified enzyme is completely free of endogenous substrate protein, and is electrophoretically homogenous. Molecular weight of the enzyme has been estimated to be 35,000 by means of Sephadex G-100. The enzymatically incorporated methyl group becomes volatile upon either acid or alkaline hydrolysis of the protein, and the product is identified as methyl alcohol. Optimum pH for the reaction is 6 in citrate-phosphate buffer, and the Km values for S-adenosyl-l-methionine with the protein isolated from calf thymus and with histone are 1.05 x 10-6 m and 1.54 x 10-6 m, respectively. The enzyme does not require any cofactor, and 50% glycerol protects the enzyme from thermal denaturation.