Degradation of myelin proteins by brain endogenous neutral protease.

A proteolytic enzyme isolated from calf brain cytosol, degraded purified myelin basic protein in the presence of Ca2+ at pH 7.0 (Singh, I. and Singh, A.K., Trans. Amer. Soc. Neurochem., 13 (1982) 119). This proteolytic enzyme also degrades basic proteins when incubated with intact myelin in the presence of Ca2+ at a neutral pH. Three hour treatment of purified myelin with this protease resulted in degradation of large basic protein and small basic protein by 73 and 89%, respectively. This proteolytic activity was inhibited by EDTA, leupeptin and low pH (pH 4.0), but was not affected by phenylmethylsulfonylfluoride, p-nitrophenylguanidinobenzoate and pepstatin A. Purified myelin preparations also contain small amounts of Ca2+-activated proteolytic activity. The fact that this is a neutral protease, endogenous to the brain, suggests that it may play a role in the degradation of myelin under physiological and pathological conditions.