title: Clostripain: characterization of the active site.
abstract: In view of the probability that clostripain (EC 3.4.22.8) is fundamentally different in structure from other known cysteine endopeptidases, it was of interest to examine the characteristics of the active site. Z-Phe-Lys-CH2S(CH3)2 irreversibly and rapidly inactivated clostripain, and leupeptin was found to be the most potent reversible inhibitor yet reported for the enzyme. Clostripain was inhibited weakly by some protein inhibitors of serine endopeptidases, and required Ca2+ for stability and activity. Mg2+ and Sr2+ were ineffective. Rapid inactivation by diethylpyrocarbonate, reversed by hydroxylamine, indicated that histidine is essential for catalytic activity. Clostripain was more rapidly inactivated by iodoacetamide than by iodoacetate, with unique pH-dependences of reaction.
authors.affiliation: Department of Biochemistry, Strangeways Research Laboratory, Worts Causeway, Cambridge, UK.
authors.forename: A A
authors.initials: AA
authors.lastname: Kembhavi
authors.forename: D J
authors.initials: DJ
authors.lastname: Buttle
authors.forename: P
authors.initials: P
authors.lastname: Rauber
authors.forename: A J
authors.initials: AJ
authors.lastname: Barrett
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology; D002413:Cations, Divalent; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors; D004047:Diethyl Pyrocarbonate / Q000494:pharmacology; D004789:Enzyme Activation; D006863:Hydrogen-Ion Concentration; D007460:Iodoacetamide / Q000378:metabolism; D007461:Iodoacetates / Q000378:metabolism; D019807:Iodoacetic Acid; D007700:Kinetics; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000494:pharmacology*; D011480:Protease Inhibitors / Q000494:pharmacology*
chemical_list: D002413:Cations, Divalent; D015853:Cysteine Proteinase Inhibitors; D007461:Iodoacetates; D009842:Oligopeptides; D011480:Protease Inhibitors; D003546:Cysteine Endopeptidases; C019913:clostripain; D004047:Diethyl Pyrocarbonate; D002118:Calcium; D019807:Iodoacetic Acid; D007460:Iodoacetamide