Conversion of myelin-associated glycoprotein (MAG) to a smaller derivative by calcium activated neutral protease (CANP)-like enzyme in myelin and inhibition by E-64 analogue.

Using the immunoblot technique, we found that an incubation of purified human myelin in 10 mM Tris-HCl buffer at pH 7.5 resulted in the conversion of the myelin-associated glycoprotein (MAG) to a smaller derivative (dMAG). Exogenously added 5 mM CaCl2 accelerated the conversion of MAG. In buffer containing more than 100 microM of EGTA, the conversion was inhibited. In addition, the existence of endogenous calcium in purified myelin was confirmed using atomic absorption spectroscopy. The conversion was also inhibited partially by one of the thiol protease inhibitors, E-64 analogue (E-64-a). These observations suggest that the conversion of MAG is mediated by calcium-activated neutral protease (CANP)-like enzyme.