Diffusional and electrostatic effects on apparent kinetic parameters of reactions catalyzed by enzyme immobilized on the external surface of a support

Diffusional and electrostatic effects on the apparent maximum reaction rate V_m^app and the apparent Michaelis constant K_m^app were investigated theoretically for a system in which an enzyme immobilized on the external surface of a solid support catalyzes a reaction according to Michaelis-Menten kinetics. In such a system, the dependence of V_m^app and K_m^app on the substrate concentration can be expressed analytically. When the support and substrate carry charges of the same sign, resulting in a repulsive force between them, both V_m^app and K_m^app decrease with increasing substrate concentration, but they never decrease below the respective intrinsic values. On the other hand, when the support and substrate carry charges of opposite sign and therefore an attractive force occurs, V_m^app decreases towards its intrinsic value, while K_m^app decreases to values below its intrinsic value in the region of high substrate concentration.