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

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Abstract
The activity of calcium‐activated neutral proteinase (mMCANP) was determined in subcellular fractions of rat brain. The CANP activity in whole homogenate and its membrane fractions including myelin was increased tenfold 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 highmolecular‐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 membranebound and soluble forms.