Protamine-induced biosilica as efficient enzyme immobilization carrier with high loading and improved stability

β-glucuronidase (GUS) was encapsulated inside mesoporous biosilica prepared via a biomimetic silicification approach. Protamine, a natural cationic polypeptide, was used to induce the condensation of sodium silicate and the enzyme GUS was thus encapsulated during the precipitation process. The enzyme loading efficiency was found to be as high as 100% within its solubility limit in aqueous solution. Furthermore, all the enzyme molecules were tightly entrapped in the biosilica particles without any leaching even under a high ionic strength condition. The biosilica particles displayed a dramatic enrichment effect toward the substrate, baicalin, through nonspecific adsorption. The catalytic activity of the encapsulated GUS was evaluated by converting baicalin into baicalein, two important effective components of herbal medicines. It was found that the thermal and pH tolerance as well as the storage and recycling stability of the encapsulated GUS were significantly enhanced compared with those of the free enzyme. Under the optimum reaction conditions (37 °C, pH 7.0), a high productivity of baicalein of 75% was obtained, only 5% lower than the case for free enzyme counterpart. No appreciable loss in activity was observed after 30-day storage, and 80% of the initial activity could be retained after 4 repeated cycles.