Determination of methylated basic amino acids with the amino acid analyzer. Application to total acid hydrolyzates of myelin basic proteins.

A procedure is described for the direct determination of methyl derivatives of basic amino acids in total acid hydrolyzates of proteins by the use of a Beckman amino acid analyzer operated in the high sensitivity mode with automatic integration. The conditions described permit the separation of ornithine, lysine, 5-hydroxylysine, N’-monomethyllysine, N”-dimethyllysine, histidine, N’-methylhistidine, ammonia, methylamine, NG,NG-dimethylarginine, NG, NIG-dimethylarginine, NG-monomethylarginine, and arginine. The procedure was used to survey purified myelin basic proteins prepared from a wide variety of species for their contents of methylated basic amino acids. Of the latter only NG, NIGdimethylarginine and NG-monomethylarginine were present. The proportions of the two methylarginines, as well as the fraction of the total arginine which they comprise varied widely depending upon the species source. No NG-monomethylarginine was detected in the hydrolyzate of the frog myelin basic protein; no methylarginines were found in that of the carp. Hydrolyzates of .fractions of contaminating proteins which had been removed from the turtle myelin basic protein during its purification were found to contain appreciable quantities of NG, NG-dimethylarginine.