Immobilization Of β-D-glucuronidase In Biomimetic Silica Gels

Silicates, primarily in the form of sol-gel composites, have been used to encapsulate a wide variety of biomolecules attributed to their significant advantages including good biocompatibility, simplicity of preparation and easy availability, but the harsh pH conditions required for chemical synthesis seriously limit their applicability. Inspired by the formation process and structure of diatoms in nature, a novel silica gel catalyzed by cationic proteins was prepared to immobilizeβ-D-glucuronidase (GUS), which can catalyze baicalin into baicalein.Protamine was used to catalyse the polycondensation of sodium silicate to prepare biomimetic protamine/silica composites. The structure, morphologies and chemical and physical properties of protamine/silica composites were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), BET nitrogen adsorption-desorption method. The mechanism of protamine-catalysed formation of silica was tentatively discussed.Catalyzed by protamine and GUS jointly, t sodium silicate polycondensation and GUS encapsulation took place simultaneously. The enzyme leakage, catalytic activity, optimum reaction conditions, kinetic parameters, and the operational and storage stability of immobilized GUS were investigated. All the enzymes has been efficiently encapsulated in the silica gels. The stability of GUS was markably enhanced after encapsulation.The TEOS polycondensation reaction was catalyzed by lysozyme and protamine respectivly. It`s been known from the comparision that lysozyme catalytic ability was more effective than protamine. The dimension of lysozyme/silica composites was bigger, while the pore diameters were smaller. The polycondensation degree catalyzed by lysozyme was lower than catalyzed by protamine.Finally, lysozyme/GUS/silica composites was prepared by TEOS polycondensation. The GUS encapsulation efficiency was 84.3±15.7 %. Compared with the free GUS, the optimal reaction temperature and pH was shifted notably after encapsulation. And the thermal and pH stability of the encapsulated enzyme was considerably improved. The recycling stability of lysozyme/GUS/silica composites was much better than of protamine/GUS/silica composites.