Catalytic, kinetic and thermodynamic properties of Bacillus pumilus FH9 keratinase conjugated with activated pectin

• Conjugation of keratinase with oxidized pectin improved its thermal stability.
• The modified enzyme had lower values of ΔH*, ΔG*, ΔS*, ΔG*E−S, and ΔG*T−S.
• Modification of the enzyme improved the values of kcat and kcat/Km.
• The modified enzyme was more tolerant to the inhibitory effects of some metal ions.

Bacillus pumilus FH9 keratinase was covalently coupled to several oxidized polysaccharides. The conjugates were evaluated for the retained activity, kinetic and thermodynamic stability. Among all preparations, the conjugated enzyme with oxidized pectin had the highest recovered activity (71.75%) and the highest thermal stability at 60 °C (t1/2 = 333 min). Compared to the native enzyme, the conjugated preparation exhibited higher optimum temperature, lower activation energy (Ea), lower deactivation constant rate (kd), higher t1/2, and higher decimal reduction time values (D) within the temperature range of 50–80 °C. The thermodynamic parameters (ΔH*, ΔG*, ΔS*) of irreversible thermal denaturation for the native and conjugated keratinase were also evaluated. The values of enthalpy of activation (ΔH*), free energy of activation (ΔG*), and free energy of transition state binding (ΔG*E−T) for keratin hydrolysis were lower for the conjugated enzyme. Moreover, there was highly significant impact on improving the values of Vmax/Km, kcat, kcat/Km, and ΔG*E−S for the modified enzyme. Both native and conjugated enzymes were slightly activated by CaCl2 and MgCl2. However, the inhibitory effects of EDTA, HgCl2 and ZnSO4 were more pronounced with the native enzyme.