Abstract
Quantitative evaluation of catalytic activity of enzymes against various substrates under several solution conditions is important to understand the catalytic mechanism. In this paper, the titration calorimetry was applied to evaluate the catalytic activity of a protease not only in the condition of peptide digestion but also in that of peptide synthesis. Two calorimetric observables, the compensation power and its integrals can be determined directly and precisely by titration calorimetry. In the hydrolytic condition, a calorimetric Lineweaver-Burk plot and non-linear least-squares method with these two observables were found to be effective to determine the enzymatic parameters precisely. Moreover, the enthalpy change accompanying the catalytic reaction can be determined with no information on the enzyme concentration and initial substrate concentration by this method with comparing the results of spectroscopic method. In the synthetic condition where the spectroscopic method can not be applied practically, the catalytic activity of the enzyme was shown to be determined quantitatively by titration calorimetry. The feature of direct observation of the reaction rate by calorimetry is considered to give us an effective and precise way to evaluate the protease activity.
