Abstract
A Lactobacillus sp. isolated from soil and capable of growing on xyloseβcontaining medium exhibited high glucose isomerase activity. The enzyme was thermostable, stable toward dialysis, and activated by heat treatment. It did not show the presence of xylose or ribose isomerase activities; the K~m~ for glucose and xylose substrates were 0.48__M__ and 0.513__M__, respectively. The heat treatment of ultrasonic crude extract gave insoluble fixed active glucose isomerase enzyme. The properties of free and immobilized enzyme in heatβfixed whole cells differed in many respects. The optimum temperature for enzyme activity changed from 70 to 85Β°C, the optimum substrate concentration changed from 1.0__M__ to 2.4__M__, and the optimum pH from 7.4 to 6.0. Co^2+^ and Mg^2+^ ions activated the enzyme when used singly, but in combination they inhibited the enzyme and Mn^2+^ had no effect on the enzyme. Free and immobilized enzymes, when used in the used in the conversions of corn and bagasse hydrolysates to fructose, gave 58, 25.6%, and 50, 27.6% conversions, respectively. Immobilized enzyme retained a significant activity for more than 30 hr and was able to operate at higher glucose concentrations showing less products inhibition effect as compared to free enzyme. In the batch process it was able to operate for about eight cycles.