Properties of α-chymotrypsin covalently immobilized on poly(acrylic acid)-grafted magnetite particles

Abstract

Enzymatic properties of α-chymotrypsin covalently immobilized on magnetite particles via graft polymerization of acrylic acid were investigated. Graft polymerization was carried out in a redox system consisting of mercapto groups introduced onto the surfaces of magnetite particles and ceric ions. α-Chymotrypsin was immobilized on magnetite particles by condensation with the carboxyl groups of the grafted poly(acrylic acid). The amount of α-chymotrypsin immobilized on 1 g of magnetite was 13-17 mg and the activity of the immobilized α-chymotrypsin (at 37 °C, pH 8.0) was 70% the maximum activity of the native enzyme. Due to immobilization, optimum pH for α-chymotrypsin shifted to a slightly higher value, whereas optimum temperature did not change. A kinetic study of the enzymatic reaction with immobilized α-chymotrypsin showed that the immobilization limited accessibility of substrate molecules to the active sites of the enzyme but caused little decrease of the maximum reaction rate. In water at 37 °C, immobilized α-chymotrypsin kept 93% of its original activity over a period of 25 days, though the native enzyme was completely deactivated within 5 days by autolytic denaturalization.