Enhanced activity of enzymes immobilized in thermoresponsive core-shell microgels

We present a quantitative study of the catalytic activity of beta-d-glucosidase from almonds adsorbed on thermosensitive microgels. The core-shell particles used as a carrier system consist of a solid polystyrene core onto which a poly(N-isopropylacrylamide) (PNiPA) network is grafted. In the swollen state of this microgel, i.e., below the critical solution temperature (LCST) of PNiPA, high amounts of enzyme can be immobilized into the PNiPA network without loss of colloidal stability. The enzymatic activity of beta-d-glucosidase in its native form and in the adsorbed state was analyzed in terms of Michaelis-Menten kinetics. Moreover, the dependence of the enzymatic activity on temperature was investigated. We demonstrate that the enzymatic activity of beta-d-glucosidase adsorbed on such a core-shell microgel is increased by a factor of more than three compared to its activity in solution. This is in marked contrast to other carrier systems that usually lead to a strong decrease of enzymatic activity. Both the high loading capacity of the carrier observed and the increase of the catalytic activity of immobilized beta-d-glucosidase are traced back to the formation of strong interactions between the enzyme and microgel. Studies by Fourier-transform infrared (FT-IR) spectroscopy identify the formation of hydrogen bonds as driving forces for the adsorption. Hydrogen bonding may also be the reason for the enhanced activity.