This report contributes to the knowledge of antiencephalitogenic spinal cord protein (SCP) with respect to three major areas of study: (1) the purification and characterization of human SCP; (2) the nature of the association of SCP with nervous tissue components and (3) purification of cyanogen bromide-derived peptides of bovine SCP.;Human SCP and a protein immunochemically identical to SCP (SCP-PN) were purified from spinal cords and peripheral nerves with 0.15 M sodium chloride, carboxy-methyl cellulose chromatography and gel filtration on Sephadex G-50 superfine. SCP and SCP-PN had estimated molecular weights of 13,700 and 14,700 daltons, respectively and had similar amino acid compositions. The isoelectric point of SCP-PN was estimated to be 9.9. Immunodiffusion analyses with anti-human SCP sera or anti-bovine SCP sera revealed that human SCP and SCP-PN are each composed of two different antigenic forms. Each antigenic form contains a distinct immunogenic domain that is identical to one of the immunogenic sites on bovine SCP.;Bovine SCP-PN is identical to the P(,2) protein found in purified peripheral nerve myeline. The bovine SCP-PN content of 0.3 M NaCl extracts of whole tissue was 1.3 mg per g of tissue. Approximately 0.33 mg of SCP-PN was found in the soluble fraction of 0.8 M sucrose homogenates of bovine peripheral nerves. Densitometry data indicated that SCP-PN decreased from 19% of the total myelin protein to less than 1% when purified myelin was extracted with 0.3 M sodium chloride or 0.05 M hydrochloric acid. The basic proteins SCP-PN and lysozyme bound to myelin and sodium chloride-extracted myeline when they were added to a suspension of myelin in 0.8 M sucrose. Pepsin, an acidic protein, did not bind to myelin. The results suggest that in 0.8 M sucrose, positively charged SCP-PN can bind to negatively charged myelin. Myelin-associated SCP-PN behaves like a peripheral membrane protein.;This interpretation is consistent with earlier research in which bovine SCP-PN was localized by immunohistological techniques in axons of peripheral nerves but not in myelin sheaths surrounding the axons. The histological fixatives acetone and 95% ethanol/ether did not render SCP-PN in whole tissue insoluble in saline. This result indicates that if a tissue section is washed with saline after fixation with acetone or 95% ethanol/ether, then most of the SCP-PN in the tissue section could be solubilized. . . . (Author\u27s abstract exceeds stipulated maximum length. Discontinued here with permission of school.) UM
