Enhancement of stability of GL-7-ACA acylase immobilized on silica gel modified by epoxide silanization

7-Aminocephalosporanic acid (7-ACA) produced by immobilized glutaryl-7-aminocephalosporanic acid (GL-7-ACA) acylase is an important starting material for the synthesis of semisynthetic cephalosporins. In this study, GL-7-ACA acylase was immobilized on silica gel modified with 3-glycidoxypropyltrimethoxysilane followed with glutaraldehyde for the production of 7-ACA. Through the experiments, optimal conditions on the immobilization of GL-7-ACA acylase were determined as follows; 12 mg/ml as an optimal concentration of GL-7-ACA acylase, 1.0 M phosphate buffer (pH 8.0) as a buffer solution, immobilization temperature of 20°C and immobilization time of 180 min. The activities of immobilized GL-7-ACA acylase obtained using low molecular weight materials were higher than that obtained immobilized GL-7-ACA acylase untreated with low molecular weight materials. Of noted importance, the highest activity of immobilized GL-7-ACA acylase was obtained by using the 0.6%(v/v) L-lysine. The effect of reducing agents in order to increase the stability of the linkage between the enzyme and the support were also investigated. The activity of immobilized GL-7-ACA acylase treated with 2%(w/w) sodium borohydride remained at almost 90% after 20 times of reuse.