The appearance of a new antigenic determinant during the degradation of myelin basic protein

Studies were undertaken to determine of a previously unrecognized or inaccessible antigenic determinant might be exposed during the course of digestion of basic protein by a normal brain enzyme. As studied by double antibody radioimmunoassay, exposure of bovine brain myelin basic protein to bovine brain cathepsin D led to the appearance of an antigenic determinant recognized by an antibody reactive predominantly with the molecular region of BP encompassing residues 79-88. The 5 major microheterogeneous components of basic protein demonstrated this phenomenon. These results indicate that a normally appearing enzyme in brain known to the present in a number of cell types including oligodendrocytes can lead to the appearance of peptides of basic protein whose antigenic determinants may not be revealed in the intact molecule. This finding suggests that a number of basic protein peptides may be released by a similar mechanism so that efforts made to detect and quantitate such peptides must be capable of recognizing their unique antigenic features.