Immobilization of ß-galactosidase and glucose isomerase onto eupergit support and using of immobilized enzymes for lactose hyrolysis and glucose isomerization

ß-Galactosidase from Kluyveromyces lactis and Glucose Isomerase (GI) from Streptomyces rubiginosus were immobilized covalently onto Eupergit C 250 L. Maximum activity of free GI was measured as 5000 U/g protein and maximum activity of immobilize GI was measured as 98092 U/g protein at predetermined optimum conditions. The KM values for free and immobilized GI were determined as 423 and 2602 mM, respectively. These results showed that catalytic efficiency of immobilized GI was about 3 fold higher than that of free GI. Reusability of the immobilized GI was investigated in a batch type stirred reactor. After 18 reuses, the residual activity of immobilized GI was about 85% of its initial activity. Thermal stabilities of free and immobilized GI determined at different temperatures were compared. Thermal stability of immobilized GI was higher than that of free GI at 60ºC for 18 h preincubation time. The residual activity for immobilized GI stored at 5ºC and 25ºC for six weeks were 71% and 43% of its initial activity, respectively. However, free GI was protected 88% and %78 of its original activity at 5ºC and 25ºC respectively for four weeks. Under the optimized conditions, KM and maximum activity of free ß-Galactosidase were determined as 933 mM and 1,7x105 ?mol glukoz dk-1 g protein-1, respectively. In this study we also determined that transgalactosylation activity of immobilized ß-Galactosidase was higher than that of its hydrolytic activity. KeyWords: Glucose isomerase, ß-galactosidase, covalent immobilization, Eupergit.