Immobilization of glucose isomerase and its reactor performance

Abstract

A reusable catalyst was prepared with heat treated whole microbial cells of $\mbox{\underline{Streptomyces}}$ by extrusion into small pieces of particulate cell aggregates, followed by glutaraldehyde treatment as a cross-linking agent for the continuous isomerization process. $\mbox{\underline{Streptomyces}}$ sp. K-45 was screened from soil, which produced relatively high enzyme activity and very stable in high temperature when it was cultured in the medium containing xylose as an enzyme inducer. Cultured cells were treated with heat of 65$^\circ$C for 15 min to improve the stability and recovery of enzyme, which were extruded into small aggregates and enzyme was fixed in the inner side of cell by glutaradehyde treatment of 5\% (w/v) for 3 hr. Immobilized whole cell products showed 25\% of the enzyme activity of that of intact whole cells. This immobilized enzyme preparation showed more broad pH optimum and the same stability against high temperature. In particular, the product showed the good physical strength. The specific activity and equilibrium conversion of glucose to fructorse were 48 units per gram of dried immobilized enzyme and 46\%, respectively, in the batch stirred reactor system and 115 units and 55\% in the continuous packed bed reactor system. The operational stability of the immobilized glucose isomerase was observed to show high stability sufficient to be adapted to the continuous reactor. The thermal inactivation of this enzyme was confirmed to obey the first order decay mode. The decay constant was $4.5\times10^{-4}hr^{-1}$ which corresponded to the half life of about 115 days, when it was allowed to catalyze the reaction with 1 M substrate solution at a residence time of 5.3 hr at 65$^\circ$C. extract (50 mg/ml) by the immobilized enzyme on aminoethyl cellulose (20 units) for 23 hr was 42 mg/ml. From this reaction mixture, 32 mg of fructose per ml was obtained (88\% conversion). In the packed bed reactor, the immobilized enzyme activity was...