Rl. Fournier et al., DEMONSTRATION OF PH CONTROL IN A COMMERCIAL IMMOBILIZED GLUCOSE-ISOMERASE, Biotechnology and bioengineering, 52(6), 1996, pp. 718-722
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.