Protonation curves of the D10N variant of endoglucanase Cel45 catalytic domain from Humicola insolens: Isothermal calorimetry and combined isoelectric focusing-electrophoresis

Titration of ionizable groups of D10N variant catalytic domain has been performed by isothermal calorimetric technique and by combined isoelectric focusing-electrophoresis in the range of pH 3-9. pK°_i and ΔH°_i related to the ionizable groups have been estimated using Lindestrøm-Lang equation. Both experimental techniques are in agreement and confirm the validity of the applied theory. Slight differences in protonation enthalpies of carboxyl groups are caused by Asp10 interaction with the other part of the macromolecule.