FIGURE 1.

Calorimetric titration of C. aestuarii oxy-Hc (16.7 μm hexamer) with successive injections of l-lactate (100 mm in the syringe, 25 × 10-μl aliquots) at pH 6.5 (A) and 8.3 (B) together with titration of CaeSS2 monomer (70 μm) at pH 6.5 (C). Upper, raw data showing the amount of heat generated after each injection of l-lactate. Lower, plot of the amount of heat generated per injection as a function of the l-lactate/Hc molar ratio. The solid lines represent the best-fitted curves of the data to a model of hexamer:l-lactate = 1:2 (A) and 1:1 (B) stoichiometry, respectively. Titration of the ligand without the protein was performed to subtract the effect of the heat because of ligand dilution.