FIGURE 2. CAS encodes a low-affinity/high-capacity Ca²⁺-binding protein.

a, Deduced amino acid sequence encoded by the CAS cDNA. Filled and open boxes show the predicted single transmembrane domain and putative Ca²⁺-binding sites, respectively. The rhodanese homology domain is underlined. b, Hydrophobicity analysis of CAS. c, ⁴⁵Ca blot analysis of the CAS N and C termini (N-t and C-t). Purified recombinant N terminus, C terminus and bovine calmodulin (CaM) were loaded, stained with Coomassie blue (left), and probed with ⁴⁵Ca in the absence (middle) or the presence of cold CaCl₂ (5 mM, right). MM, molecular marker (kDa). d, Low-affinity/high-capacity Ca²⁺ binding to the N terminus measured by equilibrium dialysis. e, Time-course analysis of CAS activation and inactivation in CAS-transfected HEK293 cells. Open and filled bars show the Ca²⁺_o concentrations of 0.1 and 2.5 mM, respectively. f, Averaged increases in relative [Ca²⁺]_i ( F_340 nm/F_380 nm) plotted as a function of applied [Ca²⁺]_o from experiments as in e (n = 20 cells). Data were fitted to a Hill equation.