title: Competitive inhibition of cathepsin C by guanidinium ions and reexamination of substrate inhibition.
abstract: Cathepsin C, a lysosomal dipeptidyl aminopeptidase, is competitively and reversibly inhibited by guanidinium ions with a Ki approximately 1.5 mM. Loss of activity is not the result of conformational change, subunit dissociation or altered mobility of the enzyme, but rather reflects a specific binding of guanidinium ions to the active site. The finding that cathepsin C is not inhibited by substrate has allowed the kinetic parameters in the presence of guanidinium ion to be determined. Guanidinium significantly decreases the Km of substrate hydrolysis, without changing Vmax. In a novel application of the transferase reaction, the Km of the nucleophile substrate has been determined (11 mM) and found not to be affected by guanidinium, indicating its inhibition of substrate binding to the S, but not the S', site. Inhibition is suggested to be the result of shielding a negative charge on the enzyme important for interaction with the substrate.
authors.affiliation: Department of Biochemistry and Molecular Biology, J. Stefan Institute, Jamova 39, Ljubljana, 1000, Slovenia. blaz.cigic@ijs.si
authors.forename: B
authors.initials: B
authors.lastname: Cigić
authors.forename: R H
authors.initials: RH
authors.lastname: Pain
mesh_terms: D000818:Animals; D020789:Cathepsin C; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D004795:Enzyme Stability; D019791:Guanidine / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D006868:Hydrolysis; D007700:Kinetics; D011489:Protein Denaturation; D013379:Substrate Specificity; D013552:Swine
chemical_list: D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; D020789:Cathepsin C; D019791:Guanidine