Preparation and characterization of immobilized glucose-phosphate isomerase

Glucose-phosphate isomerase ( d-glucose-6-phosphate ketol-isomerase, EC 5.3.1.9) isolated from rabbit muscle was covalently attached to Sepharose 4B, Akrilex C-100, Akrilex P-100 and Silochrome aldehyde, respectively. The highest immobilized activity (110 units mg −1solid) was achieved when the enzyme was bound to Akrilex C-100, a polyacrylamide support possessing carboxylic functional groups. The catalytic properties and the stability of this Akrilex-bound enzyme were studied in detail relative to those of the soluble enzyme. For both soluble and immobilized glucose-phosphate isomerase the pH optimum was about pH 8.0. The apparent optimum temperature of the immobilized enzyme was about 50°C, while that for the soluble enzyme lay between 50 and 55°C. The apparent K m for glucose 6-phosphate as substrate was higher (2 × 10 −1 mM) in the case of the immobilized enzyme. Little difference was found between the thermal stabilities of the soluble enzyme (at 45° C t 1 2 = 42 min ; at 50° C t 1 2 = 12 min ) and the immobilized enzyme (at 45° C t 1 2 = 82 min ; at 50° C t 1 2 = 10 min ). As a result of immobilization, the stability against urea was increased.