Peptides secreted from endocrine cells, paracrine cells and nerve endings regulate gastrointestinal function. Once secreted from a nerve ending a peptide will encounter peptidase enzymes which degrade the peptide, converting it to inactive fragments or to other biologically active peptides. It follows, therefore, that these peptidases play a major role in regulating gastrointestinal function, but this possibility has not received adequate attention. The objective of this proposal is to identify the major membrane-associated peptidases in human stomach tissues responsible for degradation of gastric peptides and to elucidate their physiological role. There are 5 specific aims: 1) Isolation of the enzymes; 2) Chemical characterization; 3) Enzymatic characterization; 4) Production of antibodies for immunocytochemistry and radioimmunoassay; and 5) Elucidation of the physiological importance of the peptidases. The plasma membranes will be prepared from human gastric muscle by density gradient centrifugation and peptidase activity will be solubilized with detergents and purified chromatographically. The molecular weight, isoelectric point, amino acid sequence and composition will be determined. The specificity and kinetic characteristics will be investigated using substrates of gastrin, somatostatin, gastrin releasing peptide, substance P, enkephalin and vasoactive intestinal polypeptide. Monoclonal and polyclonal antibodies will be raised to the pure enzymes for immunocytochemistry, to localize the enzyme in specific cells, radioimmunoassay, to quantify the activity in tissues, and as blocking agents of the active enzyme. The biological activities of the metabolites will be examined in several systems and the degradation of peptides will be studied using strips of gastric muscle and cultures of explanted myenteric plexus.
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