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Bovine spinal cord protein from peripheral nerve (BSCP-PN) was detected in the soluble fraction of the initial 0.8 M sucrose homogenate of bovine peripheral nerves by immunodiffusion analyses and by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The BSCP-PN in the soluble fraction of the 0.8 M sucrose homogenates was 25% of the BSCP-PN found in the soluble fraction of 0.3 M NaCl homogenates of peripheral nerve. BSCP-PN was also identified in purified bovine peripheral nerve myelin by immunodiffusion analyses and by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Densitometry data indicated that the BSCP-PN in myelin decreased from 25% of the total protein to approximately 8% when myelin was extracted with 0.3 M NaCl or 0.05 M HCl. The protein that remained in the BSCP-PN band of the NaCl-extracted myelin was identified as the periodic acid-Schiff II glycoprotein of peripheral myelin. Basic proteins such as BSCP-PN or lysozyme bound to myelin and to NaCl-extracted myelin when they were added to homogenates of myelin in 0.8 M sucrose. Pepsin, an acidic protein, did not bind to myelin under the same conditions. The results suggest that in 0.8 M sucrose, positively charged BSCPPN released from the cytoplasm by homogenization binds to negatively charged myelin; thereafter, the BSCP-PN-myelin complex remains intact until it is dissociated in media of sufficiently high ionic strength. This interpretation is consistent with the immunohistological studies which demonstrated that BSCP-PN was not in the myelin sheath but was clearly localized in axons and in, or adjacent to, the Schwann cell basement membrane.

Rat spinal cord protein (SCP) from peripheral nerves (RSCP-PN) was not detected in purified rat peripheral nerve myelin by sodium dodecyl sulfate (SDS)-polyacrylamide slab gel electrophoresis or by immunodiffusion analyses using an anti-rat SCP in peripheral nerve (RSCP-PN) serum. The slab gel electrophoretic analyses also revealed that RSCP-PN has an appreciably lower molecular size than the component of rat peripheral myelin that is identified as P2 by its molecular size of 13,600 daltons. Thus, RSCP-PN and rat P2 are unrelated proteins.

1. 1.|The human spinal cord protein (HSCP) is immunochemically closely related to the anti-encephalitogenic bovine spinal cord protein (BSCP) and immunoreactive HSCP is similarly distributed in brain, spinal cord and spinal nerve roots (a peripheral nervous tissue) in the proportions of 1 : 6 : 60. HSCP and protein immunochemically identical to HSCP (HSCP-PN), were purified from frozen spinal cords and frozen peripheral nervous tissue, respectively, by extraction with 0.15 M sodium chloride, carboxy-methyl cellulose (CM-cellulose) chromatography and gel filtration on Sephadex G-50. 2. 2.|Purified HSCP and HSCP-PN formed one band in sodium dodecyl sulfate polyacrylamide gel electrophoretograms and had estimated molecular sizes of 13 700 and 14 700, respectively. The amino acid compositions were similar except that HSCP had 16% glutamic acid and lacked half cystine while HSCP-PN contained 11.9% of glutamic acid and 1.0% of half cystine. 3. 3.|Immunodiffusion analyses with anti-HSCP or anti-BSCP sera revealed that extracts of spinal cord and spinal nerves and purified HSCP and HSCP-PN are composed of immunogenically distinct major and minor forms. The major forms and the minor forms of HSCP and HSCP-PN are identical to each other but share different antigenic amino acid sequences with BSCP. Immunoelectrophoretic profiles of spinal cord and spinal nerve extracts indicated that the major and minor HSCP antigens also existed in two different molecular forms having the electrophoretic mobilities of a β- or a γ-serum globulin. The four different molecular forms were present in purified HSCP-PN, but only the forms with γ-electrophoretic mobility were present in purified HSCP.