Differential scanning calorimetric studies on binding of N-acetyl-D-glucosamine to lysozyme

Differential scanning calorimetric (DSC) measurements were performed on the thermal denaturation of lysozyme and lysozyme complexed with N-acetyl-D-glucosamine (GlcNAc) at pH 5.00 (acetate buffer), 4.25 and 2.25 (Gly-HCl buffer). DSC data have been analyzed to obtain denaturation temperature Td, enthalpy of denaturation ΔHd, heat capacity of denaturation ΔCpd and cooperativity index Eta. From these thermodynamic parameters, the binding constant KL and enthalpy of binding ΔHL, for the weak binding of lysozyme with GlcNAc have been determined. The values of KL and ΔHL at pH 5.00 and 298 K are 42 ± 4 M-1 and -24 ± 4 kJ mol-1, respectively, and agree very well with the experimentally determined values from equilibrium and other studies. The binding constant has also been estimated by simulating the DSC curve with varying values of KL (Td) until it matches the experimental curve