Comparison of catalytic properties of free and immobilized cellobiase novozym 188.

Abstract

The enzyme cellobiase from Novo was immobilized in controlled pore silica particles by covalent binding with the silane-glutaraldehyde method with protein and activity yields of 67 and 13.7%, respectively. The activity of the free enzyme (FE) and immobilized enzyme (IE) was determined with 2 g/L of cellobiose, from 40 to 75 degrees C at pH 3.0-7.0 for FE and from 40 to 70 degrees C at pH 2.2-7.0 for IE. At pH 4.8 the maximum specific activity for the FE and IE occurred at 65 degrees C: 17.8 and 2.2 micromol of glucose/(min x mg of protein), respectively. For all temperatures the optimum pH observed for FE was 4.5 whereas for IE it was shifted to 3.5. The energy of activation was 11 kcal/mol for FE and 5 kcal/mol for IE at pH 4.5-5, showing apparent diffusional limitation for the latter. Thermal stability of the FE and IE was determined with 2 g/L of cellobiose (pH 4.8) at temperatures from 40 to 70 degrees C for FE and 40 to 75 degrees C for IE. Free cellobiase maintained its activity practically constant for 240 min at temperatures up to 55 degrees C. The IE has shown higher stability, retaining its activity in the same test up to 60 degrees C. Half-life experimental results for FE were 14.1, 2.1, and 0.17 h at 60, 65, and 70 degrees C, respectively, whereas IE at the same temperatures had half-lives of 245, 21.3, and 2.9 h. The energy of thermal deactivation was 80.6 kcal/mol for the free enzyme and 85.2 kcal/mol for the IE, suggesting stabilization by immobilization.