Abstract
Our study full filled in two main goals preparation of constitutive exochitinase with low cost, utilizing non-chitin containing agricultural wastes, and improving the thermodynamics of purified Trichoderma longibrachiatum KT693225 exochitinase by covalent coupling to sodium periodate activated agar. Central composite design (CCD) was used to improve the chemical modification of Trichoderma longibrachiatum KT693225 exochitinase. Optimum temperature for conjugated exochitinase 60 degrees C was higher than native form 40 degrees C. Covalent coupling to oxidized agar caused 432, 2.75 and 2.44-fold increase in half-life values at 50, 55 and 60 degrees C, respectively. Also, conjugated exochitinase showed higher D-values (decimal reduction time) 1790.49 compared to 733.08 min for native form at 60 degrees C. Moreover, conjugated form had lower deactivation constant rate (k(d)) 0.39 x 10(-3) min lat 60 degrees C than native form 1.7 x 10(-3) min(-1). Native exochitinase exhibited higher activation energy (E-a) 339 Kcal.mol(-1) and lower energy for denaturation (E-d) 6.88 Kcal.mol(-1) compared to 3.21 and 13.05 Kcal.mol(-1). respectively for conjugated form. The values of thermodynamic parameters for inactivation of native and conjugated exochitinase indicated that conjugation significantly decreased entropy (AS) and increased enthalpy (Delta H degrees) and free energy (Delta G degrees) of deactivation. Conjugated exochitinase exhibited higher antifungal effect against Alternaria alternate, Fusatium oxysporium and Aspergillus niger than native form. (C) 2018 Elsevier B.V. All rights reserved.