THE P₂ PROTEIN OF BOVINE ROOT MYELIN: ISOLATION AND SOME CHEMICAL AND IMMUNOLOGICAL PROPERTIES

Abstract— A small basic protein (mol.wt. 12,000), referred to as the P₂ protein, was extracted with dilute acid from delipidated bovine root myelin and purified by ion exchange chromatography on cellulose phosphate. It appeared homogeneous on polyacrylamide gel electrophoresis. The P₂ protein had a distinctly different amino acid composition than the larger basic protein (mol.wt. 18,000), referred to as the P₁ protein, that is also present in peripheral nerve myelin. It contained relatively more hydrophobic residues and much less histidine and proline. The P₂ protein conjugated with peroxidase was bound by lymph node cells and infiltrates in rabbits sensitized with whole bovine root myelin. No binding was evident with the bovine central nervous system myelin basic protein. Chemically and immunologically, the P₂ protein appears to be specific to peripheral nervous system myelin. The isolated P₂ protein produced mild clinical symptoms of experimental allergic neuritis, but no histological evidence of disease. It was suggested that the P₂ protein is an important antigen for experimental allergic neuritis, and that its antigenic determinants are likely to be conformation‐dependent.