Fig. 2.

Thermodynamical analyses of CBD1 and CBD2 Ca²⁺-binding sites using ITC. (A) ITC curves of NCX1, NCX2, and NCX3 CBD1, obtained at pH 7 in 30 mM NaCl and 130 mM KCl, confirm binding of four Ca²⁺ ions with likely comparable affinities. (B) Isoform- and splice variant-specific key-residues 552, 578, and 585 that form the CBD2 Ca²⁺-binding sites between the CD- and EF-loops. (C) Comparison of the NCX1 CBD2-AD binding isotherm (5) with those of NCX2 CBD2, NCX3 CBD2-AC, and NCX3 CBD2-B suggests binding of one, two, and three Ca²⁺ ions, respectively. (D) Comparison of NCX1 CBD12-AD and CBD12-ACDEF Ca²⁺-binding isotherms.