THERMODYNAMICS OF LIGAND (SUBSTRATE END-PRODUCT) BINDING TO ENDOXYLANASE FROM CHAINIA SP. (NCL-82-5-1) - ISOTHERMAL CALORIMETRY AND FLUORESCENCE TITRATION STUDIES

The binding of xylo-oligosaccharides to Chainia endoxylanase resulted in a decrease in fluorescence intensity of the enzyme with the formati on of 1:1 complex. Equilibrium and thermodynamic parameters of ligand binding were determined by fluorescence titrations and titration calor imetry. The affinity of xylanase for the oligosaccharides increases in the order X-2 < X-3 < X-4 less than or equal to X-5. Contributions fr om the enthalpy towards the free energy change decreased with increasi ng chain length from X-2 to X-4, whereas an increase in entropy was ob served, the change in enthalpy and entropy of binding being compensato ry. The entropically driven binding process suggested that hydrophobic interactions as well as hydrogen bonds play a predominant role in lig and binding. (C) 1998 Elsevier Science B.V. All rights reserved.