Localization of Methylated Arginine in the A1 Protein from Myelin

Methylated arginine residues are found at only one site (position 107) of the polypeptide chain of the A1 protein, as shown by analysis of tryptic and peptic peptides; these analyses show 0.2 mole of NG-dimethylarginine and 0.4-0.8 mole of NG-monomethylarginine per mole of A1 protein. The methylated arginine residues appeared to be relatively resistant to tryptic attack. Both methylated derivatives were isolated from an enzymatic digest of the A1 protein; they were identified by chromatography, electrophoresis, and degradation to citrulline, methylamine, and ornithine on alkaline hydrolysis. The phylogenetic importance of the methylated derivatives was shown by their presence in the human, monkey, bovine, rabbit, guinea pig, rat, chicken, and turtle A1 proteins at the analogous position to that of the bovine sequence:$\aligned (\text{M} & \text{ethyl})_{x}\(\text{x}=1\ \text{or}\ 2)\\ & \ \, |\\ \text{-Gly-} & \text{Arg-Gly-Leu-Ser-Leu-Ser-Arg-}\\ & 107 \endaligned $We postulate that the methylated arginine residues may serve an important role in the myelin membrane in situ by stabilization of a double-chain structure for the A1 protein; such a double-chain conformation is induced by a (proline)3sequence located nearby.