A fast evaluation of diffusion effects on bound enzyme activity.

As the kinetic behavior of bound enzymes is frequently affected by substrate diffusion between the bulk solution and the catalytic sites, a fast and simple method is proposed to detect and, subsequently, to remove diffusion effects on measured enzymic activities. The procedure makes use of the effectiveness factor concept and essentially involves the direct determination on two diagrams of the magnitude of both external and internal diffusion limitations. It requires a prior estimation of the volume and external surface area of the matrix, of the substrate external transport coefficient and internal diffusivity, and of the intrinsic Michaelis constant of the bound enzyme. However, it does not necessitate the knowledge of the quantity of bound enzyme. The two basic graphs have been calculated for Michaelis-Menten kinetics. They can also be used to evaluate diffusional effects on two-substrate reactions, as illustrated with previously published data.