The Effect of Slow Substrate Diffusion on the Activity,Stability,and Selectivity of Immobilized Enzymes: A Theoretical and Experimental Study,

摘要

A theoretical study was made to characterize and explain the activity,stability,and selectivity of immobilized enzymes when affected by pore diffusion limitation. Several moduli were defined and used as criteria for whether the activity of immobilized enzymes was limited by pore diffusion. One of them was most effectively used to represent the degree of pore diffusion limitation for each experiment. Furthermore,this modulus led to a simple and reliable method for unveiling pore diffusional disguise. Effects of substrate were coupled with the effect of pore diffusion to advance a theory of immobilized enzyme stability. Although the detailed stability behavior depended upon the degree of protection,the degree of saturation,and the initial degree of pore diffusion limitation,the theory predicted that apparent stability was generally enhanced upon immobilization,if pore diffusion was limiting. The selectively behavior with varying particle size of immobilized glucoamylase was explained in terms of pore diffusion limitation and a qualitative model of dextrin hydrolysis. Finally,attempts were made to use immobilized glucoamylase and glucose isomerase simultaneously to produce sugar mixtures from dextrin. Because of distinctly different pH optima for activity and stability of the two enzymes,operation was at a pH not optimal for either enzyme. While the extent of reversion reactions was sharply limited by use of the two-enzyme system,the compromise rendered the system commercially infeasible.