FIGURE 2. ITC of ligand binding to wild-type LacY and the C154G mutant.

Experiments were conducted at 20 °C as described under “Experimental Procedures.” A series of injections of 10 or 5 µl of 2mm TDG (A and B, respectively) or 10 µl of 0.25mm NPG (C and D) were made into 1.43 ml of 100 µm wild-type LacY (A and C) or 50 µm C154G LacY (B and D) in 50 mm NaP_i (pH 7.5)/0.01% DDM. Raw data are shown in the upper panels, and the area under each peak corresponds to the heat change (absorbed as in panel A or released as in panels B–D) upon injection of a single aliquot of TDG or NPG. The lower panels show plots of total energy exchanged (kcal·mol⁻¹ of injectant) as a function of the molar ratio of ligand to protein (i.e. the integrated data obtained from the raw data after subtraction of the heat of dilution). The solid lines in the bottom panels represent the best-fit curves to the data, using the one-site model from Microcal Origin. The thermodynamic parameters derived are listed in Table 1 and Table 2.