Representative isotherms for binding of Ca2+and Mg2+to full-length cTnC. All titrations were carried out into 100 μM full-length human WT cTnC. From left to right, the panels show the titration of 6 mM Ca2+ into apo-state full-length cTnC, 1 mM Mg2+ preincubated cTnC, and 3 mM Mg2+ preincubated cTnC. In the right most panel of this figure, 40 mM Mg2+ was titrated into full-length cTnC. The binding of Mg2+ occurs at two sets of different sites as seen in the isotherm, which contains both exothermic and endothermic components. All thermograms were fit to a “two sets-of-binding sites” model using Origin 7 MicroCal2000 ITC software package. cTnC, cardiac troponin C.