CALCIUM-ACTIVATED NEUTRAL PROTEINASE (CALPAIN) IN RAT-BRAIN DURING DEVELOPMENT - COMPARTMENTATION AND ROLE IN MYELINATION

The activity of both forms (muM and mM Ca2+-sensitive) of calcium-activated neutral proteinase (calpain) was determined in developing rat brain. Triton X-100 did not affect mcalpain activity at the earlier ages (1-5 days postpartum) whereas mcalpain activity significantly increased at 16 days and older. The mcalpain activity in brain was negligible at earlier ages (1-7 days) and the peak activity occurred between 16 and 30 days after birth. The peak activity of mcalpain in myelin was found between 16 and 30 days of age and myelin from rats older than 30 days contained 40-50% of the brain mcalpain activity. In contrast, 70-80% of the brain mcalpain activity was in cytosol at younger ages (1-10 days) and decreased to 30% with increasing age (90 days). On the other hand, mucalpain was found mainly (65-75%) associated with a membrane fraction (microsomes) before 10 days and the majority of the activity was found in cytosol (68%) between 16 and 30 days. Immunoblot studies revealed mcalpain in both myelin and cytosol from developing rat brain. These results indicate that mcalpain is present in myelin and suggest that it may be involved in the formation of myelin sheath.