An experimental verification of the theory of diffusion limitation of immobilized enzymes

Alkaline phosphatase (orthophosphoric-monoester phosphohydrolase (alkaline optimum), EC 3.1.3.1) was covalently bound to Sepharose beads. Kinetic measurements with the substrate p-nitrophenyl phosphate gave the following results. Effectiveness factors were decreasing with increasing bound activity, decreasing substrate concentration, and increasing particle radius of the beads. With decreasing effectiveness factors, the apparent Michaelis constants were decreasing. Preparations with high bound activities did not obey Michaelis-Menten kinetics at substrate concentrations much higher than the apparent Michaelis constants. The experimental results accorded quantitatively with the theory of diffusion limitation (Engasser, J.M. (1978) Biochim. Biophys. Acta 526, 301-310).