THE PRESENCE OF CYSTEINE IN FROG MYELIN BASIC PROTEIN

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Abstract
—Frog myelin basic protein, when subjected to ion‐exchange chromatography at alkaline pH, underwent conversion to a higher molecular weight form. Treatment of the latter with 2‐mercaptoethanol regenerated the monomeric basic protein. Amino acid analysis of the monomer and the higher molecular weight species after performic acid oxidation demonstrated the presence of approximately 1 mol of cysteic acid per mol of protein of molecular weight 19,700. Treatment of the monomer with the mild oxidizing agent azodicarboxylic acid bis dimethyl amide resulted in its partial conversion to the higher molecular weight form. These studies demonstrate that the frog myelin basic protein, unlike those of all other species hitherto examined, contains a single cysteinyl residue in its polypeptide chain.