title: Steady-state kinetics and thermodynamics of the hydrolysis of beta-lactoglobulin by trypsin.
abstract: Hydrolysis of beta-lactoglobulin (in an equimolar mixture of the A and B variant) by trypsin in neutral aqueous solution [pH 7.7 at 25 degrees C, ionic strength 0.08 (NaCl)] was followed by capillary electrophoresis and thermodynamic parameters derived from a Michaelis-Menten analysis of rate data obtained at 10, 20, 30, and 40 degrees C for disappearance of beta-lactoglobulin. Enthalpy of substrate binding to the enzyme and the energy of activation for the catalytic process were found to have the values, DeltaH(bind) = -28 +/- 4 kJ mol(-)(1) and E(a) = 51 +/- 18 kJ mol(-)(1), respectively. Thus, beta-lactoglobulin shows an enthalpy of activation for free substrate reacting with free enzyme of about 21 kJ mol(-)(1), corresponding to a transition state stabilization of 60 kJ mol(-)(1) when compared to acid-catalyzed hydrolysis. The catalytic efficiency of trypsin in hydrolysis of beta-lactoglobulin is increased significantly by temperature; however, this effect is partly counteracted by a weaker substrate binding resulting in an increase by only 25%/10 degrees C in overall catalytic efficiency.
authors.affiliation: Department of Dairy and Food Science, The Royal Veterinary and Agricultural University, Frederiksberg C, Denmark.
authors.forename: K
authors.initials: K
authors.lastname: Olsen
authors.forename: J
authors.initials: J
authors.lastname: Otte
authors.forename: L H
authors.initials: LH
authors.lastname: Skibsted
mesh_terms: D002851:Chromatography, High Pressure Liquid; D006868:Hydrolysis; D007700:Kinetics; D007782:Lactoglobulins / Q000737:chemistry*; D013816:Thermodynamics; D014357:Trypsin / Q000737:chemistry*
chemical_list: D007782:Lactoglobulins; D014357:Trypsin