Abstract
The existence of hysteresis phenomena in artificial enzyme membranes due to the coupling of simple kinetic enzyme properties with diffusion transport processes is reported. The intramembrane pH of a urease coating on the surface of a glass pH electrode exhibits a hysteresis loop when the pH of the bulk solution varies cyclically. The steady-state potential of a urease membrane, as a function of the substrate concentration in the bulk solution, also exhibits a memory effect. The influence of the membrane's history on its overall behavior is visualized by electron microscopy. We interpret the results in terms of a coupling between the enzyme reactions and diffusion processes, without taking into account molecular effects.