title: Peptides derived from cleavage of prosomatostatin at carboxyl- and amino-terminal segments. Characterization of tissue and secreted forms in the rat.
abstract: Tissue and secreted forms of rat prosomatostatin and its cleavage products were characterized immunochemically using high performance liquid chromatography and sequence-specific radioimmunoassays directed against somatostatin-14 (S-14), S-28-(1-12), and S-28-(1-14). Acetic or hydrochloric acid extracts of hypothalamus, pancreas, stomach, and jejunum contained seven molecular forms of Mr = 10,400 (corresponding to prosomatostatin (pro-S], Mr = 6,800 (7-kDa peptide, consisting of an NH2-terminally truncated form of pro-S), Mr = 7,600 (8-kDa peptide, corresponding to pro-S-(1-76), i.e. pro-S minus the COOH-terminal -Arg-Lys-S-14), Mr = 5,600 (5-kDa peptide, corresponding to pro-S-(33-76)) and three peptides co-chromatographing with synthetic S-14, S-28, and S-28-(1-12). Acid/ethanol extracts of these tissues contained pro-S, 8-kDa peptide, S-28, S-14, and S-28-(1-12) forms, but not the 7- and 5-kDa species. Pepstatin inhibited 7- and 5-kDa peptide formation in acetic acid extracts of tissues. The secreted forms consisted of the same five forms present in acid/ethanol or acetic acid plus pepstatin tissue extracts. The 7- and 5-kDa peptides were not secreted and appeared to be derived artifactually, presumably through the action of renin- and cathepsin D-like acid proteases. Accurate quantitation of the 8-kDa peptide by acid/ethanol extraction revealed a variable tissue distribution. Since the presence of the 8-kDa form provides evidence for direct processing of pro-S----S-14 + 8-kDa peptide, the present data suggest that pro-S----S-14 conversion is important for S-14 synthesis in the hypothalamus and pancreas, tissues rich in the 8-kDa form, but not in the stomach and jejunal mucosa, which contain low concentrations of this peptide.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D007031:Hypothalamus / Q000378:metabolism; D007413:Intestinal Mucosa / Q000378:metabolism; D008297:Male; D008970:Molecular Weight; D010179:Pancreas / Q000378:metabolism; D010436:Pepstatins / Q000494:pharmacology; D010446:Peptide Fragments / Q000032:analysis*; D011498:Protein Precursors / Q000378:metabolism*; D011863:Radioimmunoassay; D051381:Rats; D011919:Rats, Inbred Strains; D013004:Somatostatin / Q000378:metabolism*
chemical_list: D010436:Pepstatins; D010446:Peptide Fragments; D011498:Protein Precursors; C014195:Streptomyces pepsin inhibitor; D013004:Somatostatin; C028456:prosomatostatin; C031375:pepstatin