Immobilization of Candida rugosa lipase on hierarchical porous carbon monolith

Abstract

Candida rugosa lipase is immobilized into the column packed hierarchical porous carbon monolith. The carbon monolith is synthesized from resorcinol-formaldehyde (RF) gels by sol-gel polycondensation. The surface of carbon monoliths with (C-CO[subscript 2]) and without (C-N[subscript 2]) oxygen are obtained by thermal activation and carbonization, respectively. Physical adsorption by recirculation of enzyme solution is applied as immobilization technique. The carbon bead is also used as a support to study the optimal primary conditions (pH, ionic strength and protein loading). The optimal pH and ionic strength are obtained at 7 and 20 mM, respectively as a result of more protein binding ratio. However, optimal protein loading (1 mg/ml) shows the high lipase activity, while the protein binding ratio is low therefore there is a high possibility that all lipase on the support cannot fully work. Moreover, the effects of steric impediments and the enzyme distributions on the support are also significant. The short immobilization time of lipase on hierarchical porous carbon monolith indicates that enzymes rapidly fill the pores and attach on the surface of the porous carbon which result in rapid decrease in residual activity. Moreover, at low flow rate of enzyme solution the protein binding ratio can be improved because enzyme has more time to attach not only to enzyme and support, but also to enzyme and enzyme binding, whereas the lipase activity is low since the steric impediment and low enzyme distribution. For the kinetic behaviors of immobilized enzyme in the column, it is obviously seen that immobilization of lipase on different functional group surface support can change the reaction mechanism of enzyme. In case of immobilized enzyme in C-CO[subscript 2] column show the basic general enzyme-catalyzed reaction followed by Michaelis-Menten equation while immobilized enzyme in C-N[subscript 2] column show enzyme kinetic like a sigmoidal curve which might be cause from the solubility limit of the polar substrate in hydrophobic solvent. The C-N[subscript 2] column kinetic, K'' is lower than K[subscript m] from C-CO[subscript 2] column which this result indicates that C-N[subscript 2] column is less effective than C-CO[subscript 2] column. Furthermore, oxygenated surface of C-CO[subscript 2] column can help to improve more protein binding ratio.