Characterization of free and immobilized invertase regarding activity and energy of activation

Invertase from NOVO Nordisk has been immobilized in controlled pore silica particles (diameter: 0.351 mm and mean pore size: 37.5 nm) by covalent binding with the silane-glutaraldehyde method. The activity of the free and immobilized enzyme (IE) was determined with 5% (w/v) sucrose, at 35 to 65 degreesC and pH from 3 to 7. Maximum activities were found in the pH range from 5 to 6 for free invertase, and pH 4.5 for the IE. Activity yield for the IE was 24%. The Energy of Activation (Ea) was found to be a function of pH, giving for free invertase, Ea = 7.0 and 6.86 kcal/mol at pH 5.0 and 5.5, respectively, whereas for the immobilized enzyme, Ea = 6.55 and 5.93 kcal/mol at pH 4.5 and 5.0, respectively.