Calcium-dependent neutral protease activity of myelin from bovine spinal cord: evidence for soluble cleavage products of myelin proteins.

Myelin basic protein (MBP) is degraded by a calcium-stimulated protease of myelin. An attempt was made to demonstrate soluble endopeptic cleavage products of this reaction. Myelin from bovine spinal cord was incubated at pH 7.5 with 5 mM CaCl2. Protein patterns were evaluated by quantitative polyacrylamide gel electrophoresis. A selective decrease in MBP of residual myelin was accompanied by trace amounts of insoluble cleavage products only. In contrast, the buffer media contained at least 3 distinct peptides of approximate Mr's between 8 and 11 kDa. They comprised approximately 70% of total soluble protein. There was a striking concentration-dependent effect of millimolar CaCl2 on the release of both undegraded MBP and proteolytic polypeptides along with a novel polypeptide of 15 kDa. The results suggest that calcium ions are strongly affecting the retention of loosely bound myelin protein.