Fig. 2.

Mutational effects on the V_max values of the Na⁺/Ca²⁺ exchange. (A) The initial rates (t = 5s) of Na⁺-dependent ⁴⁵Ca²⁺-uptake were measured by using E. coli-derived vesicles containing the overexpressed protein of a given mutant or WT NCX_Mj (see Materials and Methods). The V_max values of the Na⁺/Ca²⁺ exchange reaction were measured for NCX_Mj mutants as described in Materials and Methods. The V_max values of the indicated mutants are presented in percentage values in comparison with WT V_max (100%). Data are presented as bars (mean ± SE). The data were derived from at least 3 independent experiments. Residues are colored according to their mutational effects on V_max, as indicated. (B) Topological positions of mutated residues are presented according to color assignments, described in panel A. (C) Cartoon representation of NCX_Mj. Mutated residues are shown as spheres and are displayed in color according to the mutational effect (see panel A). Note the specific distribution of residues belonging to group 1 (red) in the vicinity of the pore core.