The use of enzymes in media containing organic solvents is a research area of actual interest [1]. In these non-conventional conditions a question of primordial importance is the thermal stability of enzymes.

In this work the thermal inactivation kinetics of horseradish peroxidase was studied in mixtures of phosphate buffer and dimethylformamide (up to 40% v/v). Isothermal inactivation experiments were carried out in the temperature range of 70 to 85 ºC. The experimental data obtained revealed a biphasic inactivation profile and were analysed using least squares non-linear regression and a series type inactivation model [2]. The estimated reaction rate constants were used to obtain the activation energies of the inactivation process, using least squares linear regression and the Arrhenius model.

The results showed no variation in the activity of peroxidase in the mixtures studied compared to aqueous buffer alone. The series type model used described well the experimental data. The obtained kinetic parameters, reaction rate constants and activation energy, were compared as a function of dimethylformamide concentration. The occurrence of reactivation (often occurring with peroxidase) was checked after storage of the inactivated samples at 4 ºC.

Work in currently under way to study the effect of other water-miscible organic solvents on activity and stability of horseradish peroxidase.

[1] Dordick, J. S., Enzyme and Microbial Technol., 11, 194, 1989.

[2] Saraiva, J., Oliveira, J. C., Lemos, Adília and Hendrickx, M., Inter. J. of Food Sci. and Technol., 31, 223-231, 1996.