Characterization of dipeptidyl aminopeptidase I (cathepsin C) from short-finned squid

Hameed, Khwaja Shahid (1984) Characterization of dipeptidyl aminopeptidase I (cathepsin C) from short-finned squid. Masters thesis, Memorial University of Newfoundland.

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Abstract

Dipeptidyl aminopeptidase I (cathepsin C, E.C.3.14.3.1) was isolated from the hepatopancreas of the Atlantic short finned squid (Illex illecebrosus) and partially purified by the successive steps of autolysis of an acid extract, ammonium sulfate precipitation, heat treatment, ultrafiltration and affinity chromatography using p-CMB-Sepharose column. On SDS-polyacrylamide gel electrophoresis, the enzyme gave one major and one minor band corresponding to a molecular weight of about 25 and 62 kdaltons, respectively. The identification of cathepsin C is based on (1) its ability to catalyze a transferase reaction with Gly-Phe-NH₂ and a hydrolase reaction with Gly-Phe-NA or Ser-Tyr-NA at pH optima of 7 and 6, respectively; (2) the Cl⁻ ion and sulfhydryl activation of the enzyme; (3) its inhibition by known inhibitors of cathepsin C; and (4) the apparent existence of a 25 kdaltons subunit, which forms associated complexes of 50, 100 and 200 kdaltons. The dissociation and reassociation of cathepsin C in relation to its catalytic functions as a transferase and a hydrolase were studied by examining the ultrafiltration behavior of the enzyme following heat treatment or exposure to detergent or urea.

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