关键词: 热动力学, 量热法, 酶促反应, 米氏常数, 过氧化氢酶, 过氧化氢

Titration calorimetry is emerging as an important tool for characterizing interactions of biological macromolecules by virtue of its general applicability, high accuracy and precision. In this paper, two mathematical models for thermokinetics of a single-substrate enzyme-catalyzed reaction in titration period and in the stopped- titration reaction period, respectively, have been developed, by using titration calorimetry. On the basis of the titration calorimetric curve, one can use these two models to calculate not only the thermodynamic data (Δ~rH~m) but also the kinetic data (K~m and k~2) for the reaction. Thermokinetics of a well-studied single-substrate enzymatic reaction, the catalase-catalyzed decomposition of hydrogen peroxide, was thus investigated by titration calorimetry, and the molar enthalpy (Δ~rH~m) was found to be (-86.75± 0.88)kJ.mol^-^1. The Michaelis constant (K~m) for H~2O~2 and the turn-over number of the enzyme (k~2) were determined by the titration-period thermokinetic model to be (5.41±0.24)×10^-^3mol.L^-^1 and (3.58±0. 33)×10^3s^-^1, respectively, whereas the corresponding kinetic parameters calculated by the stopped-titration-reaction-period thermokinetic model were (5.43±0.21)×10^-^3mol.L^-^1 and (3.60±0. 41)×10^3s^-^1, respectively, at 298.15K and pH7.0. Reliability of the above thermokinetic models was verified by the experimental data.

Key words: THERMODYNAMICS, CALORIMETRY, MICHAELIS CONSTANT, CATALASE, HYDROGEN PEROXIDE