Calcium-activated neutral proteinase in rat brain myelin and subcellular fractions

The activity of calcium-activated neutral proteinase (mM CANP) was determined in subcellular fractions of rat brain. The CANP activity in whole homogenate and its membrane fractions including myelin was increased ten-fold following treatment with Triton X-100. The majority of the activity (60%) was in the primary particulate fractions P1 (nuclear), P2 (mitochondrial), and P3 (microsomal). Following subfractionation of each particulate fraction, most of the activity (50%) was found in the myelin-enriched fractions (P1A, P2A, and P3A) and separated at the interface of 0.32-0.85 M sucrose. Only 20-30% of the total homogenate activity was in cytosol. The enrichment in the myelin fractions resembled that for 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNPase) activity. Immunoblotting revealed that the CANP was mainly in myelin and cytosol. In addition to the presence of 72-76 Kd and 80 Kd bands, there were faint high-molecular-weight CANP bands ranging from 110-150 Kd and lower-molecular-weight forms in the region of 30-50 Kd in both purified myelin and cytosol. These studies suggested that CANP is present in myelin and cytosol and that it exists in the brain in membrane-bound and soluble forms.