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  • Title: Purification of a cysteine endopeptidase which is secreted with bioactive peptides from the epidermal glands of Xenopus laevis.
    Author: Darby NJ, Lackey DB, Smyth DG.
    Journal: Eur J Biochem; 1991 Jan 01; 195(1):65-70. PubMed ID: 1991477.
    Abstract:
    The purification is reported of an endopeptidase, XSCEP1 (Xenopus skin cysteine endopeptidase), present in skin secretions of Xenopus. The procedure involved an initial concentration of the enzyme by batchwise anion-exchange chromatography and ammonium sulphate precipitation. The proteolytic activity, determined with Z-Phe-Arg-Amc (Z, benzyloxycarbonyl; Amc, 7-amidomethylcoumarin) as substrate, was fractionated by gradient ion-exchange chromatography, yielding a major component which was purified to homogeneity by chromatography on an organomercury-agarose column. SDS/PAGE demonstrated the presence of a single protein with a molecular mass of 27 kDa. The purified enzyme, which possessed a pH optimum of 5.5, exhibited the properties of a cysteine endopeptidase; it was activated by dithiothreitol and EDTA and inhibited by the mechanism-based inhibitor trans-epoxysuccinyl-L-leucylamido(4-guanidino)butane. XSCEP1 exhibited a marked preference for substrates with a hydrophobic residue in the P1 position and arginine in the P2 position as opposed to a substrate with arginine residues in both positions. The enzyme was also able to cleave a Val-Arg-Gly sequence in a model substrate, reflecting cleavages undergone by a number of peptides present in Xenopus skin. The results point to a functional role for XSCEP1 as a putative processing enzyme.
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