Figure 2.

Characterization of photoswitchable Ca²⁺ binding affinity. (A) Ca²⁺ binding as monitored by mass spectrometry. While WT and trans X-EC12 bound three Ca²⁺ ions specifically, cis X-EC12 showed considerably weaker, predominantly nonspecific binding (Figure S4 and SI). Fits are based on a model of a single class of binding site for a maximum of three specifically bound Ca²⁺ ions. (B) The half-life of the cis state as a function of Ca²⁺ concentration, as measured by absorbance. Error bars are +1 SD from three independent experiments.