Immobilization of glucoamylase on DEAE-cellulose activated with chloride compounds

Abstract

Partially purified glucoamylase (1,4-α- d-glucan glucohydrolase, EC 3.2.1.3) from Aspergillus niger NRRL 330 has been immobilized on DEAE-cellulose activated with cyanuric chloride in 0.2 m acetate buffer, pH 4.2. In the matrix-bound glucoamylase, enzyme yield was 20 mg g −1 of support, corresponding to 40 200 units g −1 of DEAE support. Binding of the enzyme narrows the pH optimum from 3.8–5.2 to 3.6. Thermal stability of the bound glucoamylase enzyme was decreased although it showed a higher temperature optimum (70°C) than the free form (55°C). The rate of reaction of glucoamylase was also changed after immobilization. V max values for free and bound enzyme were 36.6 and 22.6 μmol d-glucose ml −1 min −1 and corresponding K m values were 3.73 and 4.8 g l −1 respectively. Free and immobilized enzyme when used in the saccharification process gave 84 and 56% conversion of starch to d-glucose, respectively. The bound enzyme was quite stable and in the batch process it was able to operate for about five cycles without any loss of activity.