title: Specific binding and degradation of somatostatin by membrane vesicles from pig gut.
abstract: Plasma membrane vesicles were prepared from the basolateral face of pig small intestinal epithelial cells and were enriched in the activity of Na+-K+-ATPase (9-fold relative to the cell homogenate) and ranged in size from 0.15 to 0.40 micron diam. Incubation of somatostatin-14 and [125I-Tyr11]-somatostatin-14 with the vesicles at 37 degrees C resulted in rapid proteolytic degradation of the peptides. Metabolites were isolated by reverse-phase high-performance liquid chromatography and identified by amino acid composition. Cleavages between Ala1-Gly2, Phe6-Phe7, Phe7-Trp8, and Thr10-Phe11 were observed, indicative of aminopeptidase and endopeptidase action. Degradation was inhibited by 1,10-phenanthroline and by bacitracin, and in the presence of these inhibitors and at 21 degrees C binding of [125I-Tyr11]somatostatin-14 to the vesicles was observed. Binding was inhibited in a concentration-dependent manner by somatostatin-14 (half-maximal inhibition at 2.0 +/- 0.1 nM) and by somatostatin-28 (0.8 +/- 0.1 nM) but not by structurally unrelated peptides. The rate of degradation of [125I-Leu8, D-Trp22, Tyr25]somatostatin-28 by basolateral membrane was less than 20 fold that of [125I-Tyr11]somatostatin-14 and a two- to three-fold enhanced binding to the vesicles was observed. Analysis of the inhibition of binding of this analogue by somatostatin-28 indicates the presence of single class of binding site with Kd = 1.3 +/- 0.3 nM. Rapid degradation but no specific binding of somatostatin-14 by brush-border membranes was observed.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.forename: M
authors.initials: M
authors.lastname: Weber
authors.forename: T
authors.initials: T
authors.lastname: Cole
authors.forename: J M
authors.initials: JM
authors.lastname: Conlon
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D000626:Aminopeptidases / Q000378:metabolism; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D010450:Endopeptidases / Q000378:metabolism; D004848:Epithelium; D007421:Intestine, Small / Q000378:metabolism*; D008854:Microscopy, Electron; D010446:Peptide Fragments / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013004:Somatostatin / Q000031:analogs & derivatives / Q000378:metabolism*; D053561:Somatostatin-28 / Q000031:analogs & derivatives; D013552:Swine; D014660:Vasoactive Intestinal Peptide / Q000378:metabolism
chemical_list: D000596:Amino Acids; D010446:Peptide Fragments; D014660:Vasoactive Intestinal Peptide; D013004:Somatostatin; C032367:somatostatin, Tyr(11)-; D053561:Somatostatin-28; C045259:somatostatin 28, Leu(8)-Trp(22)-iodo-Tyr(25)-; D010450:Endopeptidases; D000626:Aminopeptidases; D000254:Sodium-Potassium-Exchanging ATPase