[Immobilization and stabilization of papain on SiO2 particles containing amine groups]

Numerous approaches and materials have been explored for preparation of immobilization enzymes because they have considerable advantages over enzyme in bulk solution. Among present enzyme carriers inorganic materials have lower cost and more stability than organic materials. But the present inorganic materials contain less active sites and have to undergo some complicated processes before binding enzyme. So it is necessary to explore a new kind of inorganic enzyme carrier. Papain, a well characterized thiol protease kinetically and structurally, is a suitable model to compare the efficiency of various immobilization procedures. SiO2 particles containing amine groups were synthesized by synchronous hydrolysis of tetraethylorthosilicate (TEOS) and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AEAPS) in W/O Microemulsion of Triton X-100/cyclohexane/ammonium hydroxide system. The obtained particles have a diameter range from 0.3 microm to 0.5 microm, and their average size is 0.37 microm and can be controlled by adjusting water to surfactant molar ratio and water to TEOS and AEAPS molar ratio. Compared with traditional porous silica beads, these particles contain much more amine groups and their amine group content can be easily changed in the process of synthesis. Papain was immobilized on the particles which were treated by glutaraldehyde with covalent method. The optimum immobilization conditions of enzyme were as follows: enzyme load was 15 mg/g carrier, pH was 6.5. The pH and temperature optima were 6.5 and 70 degrees C for immobilized enzyme. All above indicate this kind of particle can be a good enzyme immobilization carrier.