Fig. 5. Isothermal titration calorimetry (ITC) measurements of the binding affinity between wt MBP-PDI-b′xa′ and rutin. The binding affinity of wt MBP-PDI-b′xa′ to rutin was measured by ITC method twice. With the modification of the volume of titration of rutin, we fitted the S-shape ITC curves with both upper and lower platforms. The data collected in the two parallel assays (A and B) were repeatable: the dissociation constants were 2.31 μM and 2.39 μM, the stoichiometric ratios were 0.94 and 0.86, and ΔG were −7.73 kcal mol⁻¹ and −7.71 kcal mol⁻¹, respectively.