The aim of this investigation was to purify aminopeptidase M (APM) from the muscle layer of the small intestine, to compare it with APM of the mucosa and kidney, and to examine the degradation of gastrointestinal neural and hormonal peptides by muscle APM. APM was purified from the muscle and mucosa of the pig small intestine by DEAE-Sepharose and immuno-affinity chromatography. The specific activity of APM from muscle, mucosa, and kidney was 3900, 3000, and 3800 nmol/min per mg protein, respectively (substrate [Leu5]enkephalin). Muscle and mucosa APM contained four protein bands with apparent molecular weights of 150, 110, 73, and 52 kDa. Kidney APM contained three protein bands of 150, 110, and 56 kDa. The 150, 110, and 52/56 kDa bands crossrected with an APM antiserum. APM from each tissue degraded [Leu5]enkephalin and [Met5]enkephalin, but not cholecystokinin-8, gastrin releasing peptide-10, somatostatin-14, substance P, and vasoactive intestinal peptide. The enzymes were identically inhibited by APM antiserum, amastatin, bestatin, actinonin, and 1, 10 phenanthroline. Non-mucosal APM may degrade enkephalins and terminate their biological actions.
- enkephalin degradation
- enteric neurons
- immunoaffinity chromatography
- neuropeptide degradation
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