Acid endopeptidase activity of human myelin, elicited by using exogenous myelin basic protein as enzyme substrate

Purified human myelin was incubated with exogenous myelin basic protein (MBP) at pH 4.0 to see if there is acid proteinase activity associated with myelin. Following incubation for 12 h up to 70% of MBP was degraded. On electrophoresis peptide fragments of MBP between 15.8 and 9.4 kDa were consistent with an endopeptic cleavage of MBP. Unlike the exogenous substrate MBP associated with myelin was only slightly degraded under the experimental conditions used. The results show that proteinase activity associated with isolated myelin may be elicited and further evaluated by using MBP as enzyme substrate.