Heat inactivation kinetics of Hypocrea orientalis beta-glucosidase with enhanced thermal stability by glucose

摘要

Thermal inactivation kinetics of Hypocrea orientalis beta-glucosidase and effect of glucose on thermostability of the enzyme have been determined in this paper. Kinetic studies showed that the thermal inactivation was irreversible and first-order reaction. The microscopic rate constants for inactivation of free enzyme and substrate-enzyme complex were both determined, which suggested that substrates can protect beta-glucosidase against thermal deactivation effectively. On the other hand, glucose was found to protect beta-glucosidase from heat inactivation to remain almost whole activity below 70 degrees C at 20 mM concentration, whereas the apparent inactivation rate of BG decreased to be 0.3 x 10(-3) s(-1) in the presence of 5 mM glucose, smaller than that of sugar-free enzyme (1.91 x 10(-3) s(-1)). The intrinsic fluorescence spectra results showed that glucose also had stabilizing effect on the conformation of BG against thermal denaturation. Docking simulation depicted the interaction mode between glucose and active residues of the enzyme to produce stabilizing effect. (C) 2015 Elsevier B.V. All rights reserved.