Coimmobilization of gluconolactonase with glucose oxidase for improvement in kinetic property of enzymatically induced volume collapse in ionic gels.

The object of this paper is to provide an enzymatic means to attain faster swelling or shrinking kinetics of polyelectrolyte gels that undergo volume phase transition as an immobilized enzyme reaction sets in. For this, we studied the coimmobilization of gluconolactonase (GL) with glucose oxidase (GOD). A gel used was in the shape of a small cylinder (several hundred micrometers in diameter) and composed of a lightly cross-linked copolymer of N-isopropylacrylamide and acrylic acid. GL was isolated from Aspergillus niger and purified about 100-fold. It was found that in a substrate solution containing glucose, the gel with the coimmobilized GL and GOD shrinks very rapidly. The shrinking rate was identical to that of the enzyme-free gel that undergoes a shrinking transition in response to a sudden pH change of the outer medium from 7 to 5. This indicates the rate-limiting step in the shrinking process to be diffusion of the networks, but not the enzyme reaction. In the gel with singly immobilized GOD, a very slow shrinking was observed because the process is governed by the enzyme reaction. These results were discussed in full in connection with an enzymatically induced decrease in pH within and in the vicinity of the gel phase. As a result, it has become apparent that the faster shrinking kinetics in the coimmobilized enzyme system is attained by the GL-catalyzed hydrolysis of D-glucono-delta-lactone resulting from the oxidation of glucose with GOD.