Diffusion and the limiting substrate in two‐substrate immobilized enzyme systems

Abstract

The effects of mass transport resistances on two-substrate immobilized enzyme systems are investigated theoretically. It is shown that the effects of mass transport resistances on the overall reaction rate are related mainly to the transport of the limiting substrate. In the absence of external mass transport resistances, the limiting substrate can be identified by knowing only the ratio of the bulk substrate concentrations, the permeability of the support to the two substrates, and the stoichiometry of the reaction. However, a combination of internal and external mass transport resistances may result in the other substrate becoming limiting. These effects are most significant when the mass transport resistances are high. Applications in the design of enzyme electrodes and chemical reactors are discussed.

Model of a two-substrate enzyme electrode for glucose

“…The model is formulated completely by incorporating the characteristic reaction rate expression for the soluble enzyme or an appropriate approximation in the dimensionless reaction rate expression. For membranes containing immobilized glucose oxidase and excess catalase, the following reaction rate expression is useful: r(cg, c0) V max^g^o c0 + K0'Cg (20) This expression is an approximation to the more general ping-pong rate expression determined for the soluble enzyme (18). The rationale for use of this expression is discussed below.…”

Common Causes of Glucose Oxidase Instability in In Vivo Biosensing: A Brief Review

“…9 The internal factors include lead detachment, electrical short, membrane delamination, membrane degradation, and sensing-enzyme degradation. Gough and coauthors [1][2][3][4][5][6][7][8] state that GOx degradation stems from either spontaneous inactivation or peroxide mediated inactivation. They suggest that spontaneous inactivation occurs throughout the immobilized enzyme phase but inactivation occurs by an unknown mechanism.…”

“…Glucose sensor instability depends on many environmental and internal factors. Gough and coauthors [1][2][3][4][5][6][7][8] published several papers elaborating on the origins of these environmental and internal factors. Environmental factors occur in vivo due to lack of biocompatibility and include membrane biofouling, electrode passivation, and fibrous encapsulation.…”

“…We suggest that LMWM degradation and epoxy formation within the immobilized enzyme layer encompasses the spontaneous inactivation observed by Gough and coauthors. [1][2][3][4][5][6][7][8] The work of Gough and coauthors [1][2][3][4][5][6][7][8] motivated synthesis of this review.…”

Effect of Quaternization of the Glucose Oxidase “Wiring” Redox Polymer on the Maximum Current Densities of Glucose Electrodes

“…Katakis and Hauser, following Leypold and Gough, − solved analytically coupled differential equations for the transport and reaction rates in “wired” enzyme electrodes for the limiting case of low enzyme loading and thin sensing films. Experiments confirmed that when the sensing film was sufficiently thin and the enzyme loading was low, the transfer of electrons from the active center of the enzyme to the redox center on the polymer constituted the rate-limiting step.…”