In vivo methylation of an arginine in chicken myelin basic protein.

The amino acid sequence around the sole methylarginine residue in chicken myelin basic protein was determined and was found to be similar to that previously reported for mammalian myelin basic protein. The ratio NG, N'G-dimethylarginine: NG-monomethylarginine:arginine was approximately 1.3:0.9:1.0. No NG, NG-dimethylarginine was detected in the protein. The in vivo incorporation of methyl groups from [methyl-3H]methionine into methylarginines in myelin was found to occur readily in 2-day-old chickens. Radioactively labelled NG,N'G-dimethylarginine and NG-monomethylarginine in myelin were derived solely from myelin basic protein. Radioactivity was also incorporated into NG,NG-dimethylargnine, although this was not derived from myelin basic protein. As NG-monomethylarginine was easily separated from the dimethylarginines, and as it was derived from myelin basic protein, it may be a good marker for myelin basic protein turnover in vivo. A time course study of the incorporation showed that radioactivity was incorporated into NG-monomethylarginine up to 6 h after injection, and decayed slowly, with an apparent half-life of about 40 days.