A MATHEMATICAL-MODEL FOR THE GENERATION AND CONTROL OF A PH GRADIENT IN AN IMMOBILIZED ENZYME-SYSTEM INVOLVING ACID GENERATION

An optimal pH control technique has been developed for multistep enzym atic synthesis reactions where the optimal pH differs by several units for each step. This technique separates an acidic environment from a basic environment by the hydrolysis of urea within a thin layer of imm obilized urease. With this technique, a two-step enzymatic reaction ca n take place simultaneously, in proximity to each other, and at their respective optimal pH. Because a reaction system involving an acid gen eration represents a more challenging test of this pH control techniqu e, a number of factors that affect the generation of such a pH gradien t are considered in this study. The mathematical model proposed is bas ed on several simplifying assumptions and represents a first attempt t o provide an analysis of this complex problem. The results show that, by choosing appropriate parameters, the pH control technique still can generate the desired pH gradient even if there is an acid-generating reaction in the system. (C) 1998 John Wiley & Sons, Inc.