Figure 7.

Cd²⁺ competes Ca²⁺ off C2A, resulting in protein dissociation from the membrane. (A) Fluorescence emission spectra of C2A (0.5 µM) in the presence of LUVs (150 µM) and saturating [Ca²⁺] (160 µM) collected at increasing [Cd²⁺]. The intensity of the dansyl band decreases, with the concomitant increase of the intensity of the Trp emission band, indicating C2A displacement from the membrane. (B) FRET-monitored competition experiments between Ca²⁺ and Cd²⁺ in the presence of LUVs. The intensity of dansyl emission band plotted as a function of Cd²⁺/Ca²⁺ (black trace; [Ca²⁺]=160 µM) and Ca²⁺/Cd²⁺ concentration ratios (blue trace; [Cd²⁺]=160 µM). While Cd²⁺ displaces Ca²⁺ from the protein and results in membrane dissociation, Ca²⁺ cannot displace Cd²⁺ from C2A and support membrane association.