PURIFICATION AND CHARACTERIZATION OF A HIGHLY THERMOSTABLE GLUCOSE-ISOMERASE PRODUCED BY THE EXTREMELY THERMOPHILIC EUBACTERIUM, THERMOTOGA-MARITIMA

Thermotoga maritima, among the most thermophilic eubacteria currently known, produces glucose isomerase when grown in the presence of xylose. The purified enzyme is a homotetramer with subunit molecular weight of about 45,000. It has a number of features in common with previously described glucose isomerases-pH optimum of 6.5 to 7.5, presence of active-site histidine, requirement for metal cations such as Co2+ and Mg2+, and preference for xylose as substrate. In addition, it has significant sequence/structural homology with other glucose isomerases, as shown by both N-terminal sequencing and immunological crossreactivity. The T. maritima enzyme is distinguished by its extreme thermostability-a temperature optimum of 105 to 110-degrees-C, and an estimated half-life of 10 minutes at 120-degrees-C, pH 7.0. The high degree of thermostability, coupled with a neutral to slightly acid pH optimum, reveal this enzyme to be a promising candidate for improvement of the industrial glucose isomerization process.