Abstract— Myelin was purified from the peripheral nervous system (PNS) of several species. The protein composition of these preparations was examined by discontinuous polyacrylamide gel electrophoresis in buffers containing sodium lauryl sulphate. Proteins characteristic of all samples include, in order of increasing mobility: a series of high molecular weight proteins, the major peripheral nerve protein (P0), two uncharacterized proteins, and two basic proteins (P1 and P2). Quantitative results, obtained by densitometry of gels stained with Fast Green showed differences in protein distribution, both between species, and from different types of nerves obtained from the same animal. The relative amounts of P1 and P2 proteins were the most variable; e.g. myelin from guinea‐pig sciatic nerve had little or no P2 protein, whereas 15 per cent of the myelin protein of beef posterior intradural root was Pz protein. P0, P1 and P2 proteins from rabbit sciatic nerve and P0 and P2 proteins from beef dorsal and ventral intradural roots were purified and their amino acid compositions were determined. Our results indicated that the P1 protein is very similar in size and amino acid composition to the basic protein of central nervous system myelin, whereas the P0 and P2 proteins are unique to the PNS.

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Methylated arginine residues are found at only one site (position 107) of the polypeptide chain of the Al 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 Al protein. The methylated arginine residues appeared to be relatively resistant to tryptic attack. Both methylated derivatives were isolated from an enzymatic digest of the Al 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 Al proteins at the analogous position to that of the bovine sequence: (Methyl). (x = 1 or 2)

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A highly encephalitogenic peptide whose structure resembles the sequence of amino acids surrounding the single tryptophan residue in the encephalitogenic A1 protein from bovine myelin was synthesized. This peptide is similar in the sequence to peptic peptide E and tryptic T27, derived directly from the A1 protein, and is as active on a molar basis as the A1 protein. The major disease-inducing site of the A1 protein resides in a linear sequence of nine amino acids: H-Phe-Ser-Trp-Gly-Ala-Glu-Gly-Gln-Lys-OH. This region of the A1 protein is apparently the major encephalitogenic determinant since specific modification of the tryptophan residue in the A1 protein with 2-hydroxy-5-nitrobenzyl bromide destroyed its encephalitogenic activity.

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