Methylation of Protein by Calf Spleen Methylase
Abstract A purified enzyme from calf spleen has been found to methylate, in the presence of S-adenosyl-l-methionine-14CH3, a number of added crystalline proteins such as ovalbumin, pepsin, or human serum albumin. Before purification, the enzyme is capable of methylating endogenous protein present in spleen extracts. Incubation of crystalline ovalbumin and purified spleen methylase in the presence of S-adenosyl-l-ethionine-ethyl-1-C14 results in an incorporation of ethyl groups which is less than 3% of the incorporation of methyl groups. Acid or alkaline hydrolysis of radioactive enzymatically methylated ovalbumin yields a steam-distillable, radioactive compound which has been identified as methanol. Chemical studies have revealed that spleen protein methylase, unlike other known protein methylases, methylates an amino acid residue other than lysine or arginine, and, therefore, it represents a new enzymatic protein methylation reaction.