Figure 4.

Isothermal titration curves of MTA binding to salmon testes DNA at 25°C. (A) Titration of a Mg²⁺–MTA complex in HPS buffer (pre-formed in the syringe of the ITC apparatus) into DNA in the same buffer solution without added Mg²⁺. ITC raw data are shown in the top panel, while the lower panel shows the uncorrected binding isotherm. (B) Heat of dilution of an MgCl₂ solution titrated into a DNA solution in HPS buffer. The distribution of the heats of dilution of Mg²⁺ corresponds to a ΔH ∼ −60 cal mol⁻¹. (C) Heat change induced in an ITC experiment by adding Mg²⁺–MTA complexes into buffer in the absence of DNA (open squares). The panel also shows the uncorrected isothermal titration curve of the titration of Mg²⁺-MTA complex into DNA (black squares) redrawn from (A). (D) Corrected binding isotherm resulting from integration with respect to time, with correction for the measurements presented in (B and C) (see also Figure S3). The heats obtained for each injection in (C) were subtracted from the corresponding raw value (open squares) in the same panel.