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

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.