Quinine-Fab binding. (A-B) Isothermal titration calorimetry. Titrations of quinine into 314.1 (A) and 314.3 (B) IgG in the calorimetry cell are as described in “Methods.” Because the 2 binding sites in IgG bind quinine independently, the results are expressed in terms of the concentration of half of an IgG, ie, the concentration of heavy and light chains. (C) Gel-filtration chromatography of the α_IIbβ₃ headpiece, with or without Fab 314.1, with and without quinine, and with and without quinine in the running buffer.