Studies on characters of immobilizing penicillin G acylase on a novel composite support PEI/SiO2

Polyethyleneimine (PEI) was grafted onto the surface of silica gel particles via the coupling effect of γ-chloropropyl trimethoxysilane (CP), and the novel composite support PEI/SiO2 was prepared. The chemical structure and composition were characterized with infrared spectrum and conductometric titration, and its surface electrical property was also measured. The character of the immobilized enzyme on the novel composite support was studied by using penicillin G acylase as a model enzyme. By using the double functional group reagent glutaraldehyde, penicillin G acylase was immobilized on the composite support PEI/SiO2. The effects of various immobilization conditions on the apparent activity of the immobilized enzyme were examined, such as time, the used amount of glutaraldehyde, pH value and so on. The mechanism of immobilizing enzyme was probed into. The suitable temperature and pH value for using the immobilized enzyme to catalyze the hydrolysis reaction of penicillin G were researched, and the continuous operating stability of the immobilized enzyme was examined. The experiment results show that the combining of less quantity of covalent linking with a great deal of physical adsorption caused by a great number of amino groups in PEI macromolecules not only can lead to faster immobilizing of penicillin G acylase, but also can result in retaining well the conformation of enzyme, and the immobilized enzyme has higher activity. Compared to the free enzyme, the ranges of suitable temperature and pH value are all widened as the immobilized enzyme is used, the thermal stability of the immobilized enzyme is also enhanced distinctly, and the immobilized enzyme has better continuous operating stability and its activity can keep at the level of 87.5% of fresh one all along after using 15 times repeatedly.