A mathematical model for the generation and control of a pH gradient in an immobilized enzyme system involving acid generation

Abstract

An optimal pH control technique has been developed for multistep enzymatic 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 immobilized urease. With this technique, a two‐step enzymatic reaction can take place simultaneously, in proximity to each other, and at their respective optimal pH. Because a reaction system involving an acid generation represents a more challenging test of this pH control technique, a number of factors that affect the generation of such a pH gradient are considered in this study. The mathematical model proposed is based on several simplifying assumptions and represents a first attempt to 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. ©1998 John Wiley & Sons, Inc. Biotechnol Bioeng 57: 394‐408, 1998.

Is enzyme immobilization a mature discipline? Some critical considerations to capitalize on the benefits of immobilization

“…110,[274][275][276][277][278][279][280] The disulfide bonds may be broken under reducing conditions, or if the media is able to oxidize the disulfide, or even if there are compounds in the reaction media bearing thiol groups. 53,[219][220][221][222] Using cyanogen bromide supports, the enzyme is immobilized via several kinds of bond, and some of them are reversible, enabling enzyme release. [281][282][283][284][285][286] Enzyme immobilization via interaction of mainly His groups belonging to the enzyme (but also Cys, Tyr and others) with immobilized metal chelates may also have problems, [287][288][289][290][291] since the interaction may be broken at certain values of pH or if the medium contains particular compounds (e.g., His free amino acids or contained in peptides if using immobilized proteases to hydrolyze proteins).…”

“…This can be problematic if the researcher checked enzyme release under initial conditions alone. 202 Even if the pH is controlled during the reaction, if the enzyme volumetric activity is high enough and the support particle is large enough, an internal pH gradient may be formed inside the biocatalyst particle [217][218][219][220][221][222][223] (this will be specifically discussed later in this review), and this may also facilitate the release of enzyme molecules located in the inner part of the particle. 224,225 Furthermore, the ionic strength attributed to the substrate and the product may be very different.…”

Regulation of interfacial chemistry by coupled reaction–diffusion processes in the electrolyte: A stiff solution dynamics model for corrosion and passivity of metals

“…Chemistry are a few areas, besides corrosion, where the proposed model will be relevant. In particular, pH generation and control [17] by diffusion and reaction is crucial in many systems including the human body.…”

“…Electrocatalysis, Enzymatic Kinetics, Batteries and Fuel Cells, and Industrial/ Environmental Chemistry are a few areas, besides corrosion, where the proposed model will be relevant. In particular, pH generation and control [17] by diffusion and reaction is crucial in many systems including the human body. (-4) A/dm 2 ; the solid horizontal line is solubility product of ferrous hydroxide.…”