ThepH dependence of the equilibrium constantK
Hyd for the hydrolysis of the Lys15-Ala16 reactive-site peptide bond in bovine pancreatic trypsin inhibitor (aprotinin) |
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Authors: | Jürgen Siekmann Herbert R Wenzel Eduard Matuszak Eberhard von Goldammer Harald Tschesche |
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Institution: | 1. Universit?t Bielefeld, Fakult?t für Chemie, Lehrstuhl für Biochemie, Bielefeld 1, D-4800, Postfach 8640, Federal Republic of Germany 2. Institut für Biophysik, Universit?t Witten/Herdecke, D-5810, Witten, Federal Republic of Germany
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Abstract: | ThepH dependence of the equilibrium constant KHyd for the hydrolysis of the Lys15-Ala16 reactive-site peptide bond of the bovine pancreatic trypsin inhibitor (aprotinin) was investigated over thepH range 2.3–6.5. Solutions of aprotinin, modified aprotinin with the Lys15-Ala16 peptide bond cleaved and mixtures of both species were incubated with 10 mol% porcine β-trypsin. The state of equilibrium was determined by analytical cation-exchange HPLC. The KHyd values obtained did not exactly obey the simple equation of Dobry et al. (1952), which had to be used in an extended form with two additional parameters for a satisfactory fit. ThepH-independent equilibrium constant is 0.90 and thepK values of the Lys15 carboxyl group and of the Ala16 amino group are 3.10 and 8.22, respectively. ThepK of an additional group is apparently perturbed by the peptide-bond hydrolysis. It is 4.60 in the native and 4.40 in the modified aprotinin. |
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