The addition of Co2+ enhances the catalytic efficiency and thermostability of recombinant glucose isomerase from Thermobifida fusca

Abstract

Glucose isomerase is an important industrial enzyme that catalyzes the reversible isomerization of glucose to fructose. In this study, the effect of cobalt ions (Co2+) on the catalytic efficiency and thermostability of recombinant glucose isomerase from Thermobifida fusca was analyzed. The activity of glucose isomerase from engineered Escherichia coli supplemented with 1mM Co2+ (C-GI) reached 41U/ml, 2.1-fold higher than enzyme prepared from E. coli without additive (GI). The purified C-GI also exhibited an increased specific activity (23.8U/mg compared to 12.1U/mg for GI) and a greater thermostability (half-life of 17h at 75°C, 11.3-fold higher than GI (1.5h)). The optimal temperature for C-GI shifted from 80°C to 85°C and demonstrated higher activity over pH 7.0–9.0. The kcat/Km value of C-GI (89.3M−1s−1) for the isomerization of glucose to fructose was nearly 1.75-fold higher than that of GI. In addition, the engineered cells were immobilized with the method of flocculation-cross linking. The immobilized cells supplemented with 1mM Co2+ (C-IGI) had a better operational performance than cells without additives (IGI); at the end of 6 cycles, the conversion rate of C-IGI was still 43.1%, meeting the conversion rate requirement.