Kinetic and thermodynamic properties of purified alkaline protease from Bacillus pumilus Y7 and non-covalent immobilization to poly(vinylimidazole)/clay hydrogel

The characterization of the hydrogel was performed using Fourier-transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. Purified Bacillus pumilus Y7-derived alkaline protease was immobilized in Poly (vinylimidazole)/clay (PVI/SEP) hydrogel with 95% yield of immobilization. Immobilization decreased the pH optimum from 9 to 6 for free and immobilized enzyme, respectively. Temperature optimum 3°C decreased for immobilized enzyme. The K _m, V _m, and k _cat of immobilized enzyme were 4.4, 1.7, and 7.5-fold increased over its free counterpart. Immobilized protease retained about 65% residual activity for 16^th reuse. The immobilized protease endured its 35% residual activity in the material after six cycle's batch applications. The results of thermodynamic analysis for casein hydrolysis showed that the ΔG^≠ (activation free energy) and ΔG^≠ _E-T (activation free energy of transition state formation) obtained for the immobilized enzyme decreased in comparison to those obtained for the free enzyme. On the other hand, the value of ΔG^≠ _ES (free energy of substrate binding) was observed to have increased. These results indicate an increase in the spontaneity of the biochemical reaction post immobilization. Enthalpy value of immobilized enzyme that was 2.2-fold increased over the free enzyme indicated lower energy for the formation of the transition state, and increased ΔS^≠ value implied that the immobilized form of the enzyme was more ordered than its free form.