The kinetics of cellulase in reverse micelles using an isothermal titration microcalorimetry technique

Abstract

We report the activities of cellulase in reverse micelles was investigated via microcrystalline cellulose as substrates using isothermal titration microcalorimetry (ITC). The ITC can record the heat evolved in enzyme catalysis reactions, and the resulting thermal power can be further used to calculate the apparent Michaelis constant (KM) and the maximum rate of the reaction (Vm) of enzymes. Importantly, ITC in enzyme kinetics is not limited to soluble systems—it is equally effective in monitoring reaction heats in suspensions. The reverse micelles studied here were formed by polyoxyethylene lauryl ether (Brij35), n-hexanol, and cyclohexane. The effects of ωo, the molar ratio of water to surfactant, pH, temperature, and ionic effects on the kinetics of cellulase in Brij-35/n-hexanol/cyclohexane reverse micelles were investigated, and the optimal conditions of ωo (the molar ratio of water to surfactant), pH, and temperature were obtained. Furthermore, K+, Na+, Cl−, and NO3− enhanced the cellulase activity in Brij-35/n-hexanol/cyclohexane reverse micelles; Mg2+, Ba2+, SO42-, and SO32- inhibited entrapped cellulase. These results are of interest in understanding the kinetics of cellulase in reverse micelles. The findings might have industrial applications for reverse micelles system that degrades cellulose into sugar.