DEMONSTRATION OF PH CONTROL IN A COMMERCIAL IMMOBILIZED GLUCOSE-ISOMERASE

The synthesis of a variety of important biochemicals involves multiste p enzyme-catalyzed reactions. In many cases, the optimal operating pH is much different for the individual enzymatic steps of such synthesis reactions. Yet, it may be beneficial if such reaction steps are combi ned or paired, allowing them to occur simultaneously, in proximity to one another, and at their respective optimal pH. This can be achieved by separating the microenvironments of the two steps of a reaction pat hway using a thin urease layer that catalyzes an ammonia-forming react ion. In this article, the pH control system in a commercial immobilize d glucose (xylose) isomerase pellet, which has an optimal pH of 7.5, i s demonstrated. This system allows the glucose isomerase to have near its optimal pH activity when immersed in a bulk solution of pH 4.6. A theoretical analysis is also given for the effective fraction of the i mmobilized glucose isomerase, which remains active when the bulk pH is at 4.6 in the presence of 20 mM urea versus when the bulk pH is at it s optimal pH of 7.5. Both theoretical and experimental results show th at this pH control system works well in this case. (C) 1996 John Wiley & Sons, Inc.