title: Membrane-bound enzymes and their role in processing of the dynorphins and of the proenkephalin octapeptide Metenkephalin-Arg-Gly-Leu.
abstract: Synaptosomal membrane (SPM) bound exo- and endopeptidases cleave the dynorphins and Met-enkephalin-Arg-Gly-Leu at several sites to produce shorter fragments; among these are dynorphin 1-8 from 1-17, and Met-enkephalin from Met-enkephalin-Arg-Gly-Leu. The most vulnerable site is the Tyr-Gly bond cleaved by membrane-bound aminopeptidase(s), with the shorter peptides degraded more rapidly than the longer ones. A purified metalloendopeptidase sensitive to phosphoramidon inactivates the shorter peptide sequences at the Gly3-Phe4 bond, and the 1-13 and 1-17 sequences also at the Arg7-Ile8 bond. The kcat/Km ratios for purified metalloendopeptidase were 20-30 times higher for Leu-enkephalin and the proenkephalin octapeptide than for dynorphins 1-8, 1-13, and 1-17. Dynorphins 1-13 and 1-17 may serve as precursors for the widely distributed CNS neuropeptide dynorphin 1-8 since they were cleaved by a separate SPM endopeptidase insensitive to phosphoramidon. SPM monocarboxypeptidase converted dynorphin 1-13 to 1-12 (release of Lys) and dipeptidyl carboxypeptidase converted dynorphin 1-8 to 1-6; enkephalin octapeptide served as a precursor of Met-enkephalin by sequential action (release of Leu and Arg-Gly) of both carboxypeptidases.
mesh_terms: D000818:Animals; D001921:Brain / Q000201:enzymology / Q000378:metabolism*; D002384:Catalysis; D004399:Dynorphins / Q000378:metabolism*; D010450:Endopeptidases / Q000378:metabolism*; D004744:Enkephalin, Methionine / Q000031:analogs & derivatives* / Q000378:metabolism; D020689:Exopeptidases; D066298:In Vitro Techniques; D007668:Kidney / Q000201:enzymology; D010447:Peptide Hydrolases / Q000378:metabolism*; D051381:Rats; D013570:Synaptic Membranes / Q000201:enzymology; D013574:Synaptosomes / Q000201:enzymology
chemical_list: D004744:Enkephalin, Methionine; D004399:Dynorphins; C033453:enkephalin-Met, Arg(6)-Gly(7)-Leu(8)-; D010450:Endopeptidases; D020689:Exopeptidases; D010447:Peptide Hydrolases