title: Kinetics of inhibition of bovine cathepsin S by bovine stefin B.
abstract: The kinetics of the complex formation between bovine cathepsin S and bovine stefin B was studied by conventional and stopped-flow techniques. The inhibition at low inhibitor concentrations was tight and reversible (kass = 5.8 x 10(7) M-1.s-1, kdiss = 4.9 x 10(-4) s-1 at pH 6.0 and 25 degrees C), whereas at higher inhibitor concentrations it was pseudo-irreversible (kass = 6.14 x 10(7) M-1.s-1). The complex was formed directly lacking the fast pre-equilibrium step with the dissociation equilibrium constant of approximately 8 pM. The competitive nature of inhibition was confirmed. The kass was found to be pH-independent between pH 6.0 and 7.5 and decreased at lower or higher pH values in a way that strongly suggests involvement of two ionizable groups in the interaction (pKi = 5.2, pK2 = 8.3). The enzyme-substrate interaction seems to be influenced by different ionizable groups (pKi = 4.4, pK2 = 7.8).
authors.affiliation: Department of Biochemistry and Molecular Biology, J. Stefan Institute, Jamova, Ljubljana, Slovenia.
authors.forename: B
authors.initials: B
authors.lastname: Turk
authors.forename: A
authors.initials: A
authors.lastname: Colić
authors.forename: V
authors.initials: V
authors.lastname: Stoka
authors.forename: V
authors.initials: V
authors.lastname: Turk
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D002403:Cathepsins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002417:Cattle; D055313:Cystatin B; D015891:Cystatins / Q000378:metabolism / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D013050:Spectrometry, Fluorescence; D013696:Temperature
chemical_list: D015891:Cystatins; D055313:Cystatin B; D002403:Cathepsins; C028217:cathepsin S