title: Enzymes processing somatostatin precursors: an Arg-Lys esteropeptidase from the rat brain cortex converting somatostatin-28 into somatostatin-14.
abstract: The post-translational proteolytic conversion of somatostatin-14 precursors was studied to characterize the enzyme system responsible for the production of the tetradecapeptide either from its 15-kDa precursor protein or from its COOH-terminal fragment, somatostatin-28. A synthetic undecapeptide Pro-Arg-Glu-Arg-Lys-Ala-Gly-Ala-Lys-Asn-Tyr(NH2), homologous to the amino acid sequence of the octacosapeptide at the putative Arg-Lys cleavage locus, was used as substrate, after 125I labeling on the COOH-terminal tyrosine residue. A 90-kDa proteolytic activity was detected in rat brain cortex extracts after molecular sieve fractionation followed by ion exchange chromatography. The protease released the peptide 125I-Ala-Gly-Ala-Lys-Asn-Tyr(NH2) from the synthetic undecapeptide substrate and converted somatostatin-28 into somatostatin-14 under similar conditions (pH 7.0). Under these experimental conditions, the product tetradecapeptide was not further degraded by the enzyme. In contrast, the purified 15-kDa hypothalamic precursor remained unaffected when exposed to the proteolytic enzyme under identical conditions. It is concluded that this Arg-Lys esteropeptidase from the brain cortex may be involved in the in vivo processing of the somatostatin-28 fragment of prosomatostatin into somatostatin-14, the former species being an obligatory intermediate in a two-step proteolytic mechanism leading to somatostatin-14.
mesh_terms: D000818:Animals; D002540:Cerebral Cortex / Q000201:enzymology*; D002845:Chromatography; D007700:Kinetics; D008297:Male; D010446:Peptide Fragments / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D051381:Rats; D013004:Somatostatin / Q000378:metabolism*; D053561:Somatostatin-28; D013379:Substrate Specificity
chemical_list: D010446:Peptide Fragments; D013004:Somatostatin; D053561:Somatostatin-28