The P2 Protein of Bovine Root Myelin: Partial Chemical Characterization¹

The P2 protein of bovine root myelin has chemical characteristics which differentiate it from other myelin basic proteins. The tryptic peptide map of the bovine P2 protein is distinctly different from the map of either the rabbit PI protein or the bovine CNS myelin basic protein. The tryptic peptides of the P2 protein show no overlap in either map positions or amino acid content with the peptides of the CNS myelin basic protein. Analysis of the individual peptides in the P2 map accounted for all of the amino acids present in the analysis of the whole protein. The P2 protein has a blocked NH 2 ‐terminus, lysine at its COOH‐terminus and no hexosamine. CD studies revealed that the P2 protein has a very stable β ‐structure in aqueous solution at neutral or basic pH and retains much of this structure in acid and in 8 M urea. It is suggested that these structural properties are relevant to the dual role of the P2 protein as a membrane constituent and as an antigen.