title: In vitro calibration of the equilibrium reactions of the metallochromic indicator dye antipyrylazo III with calcium.
abstract: The equilibrium reactions of the metallochromic indicator dye Antipyrylazo III with calcium at physiological ionic strength have been investigated spectrophotometrically. Dye absorbance as a function of wavelength was measured at various total dye and calcium concentrations. Analysis of the absorbance spectra indicated that at pH 6.9 at least three calcium:dye complexes form, with 1:1, 1:2, and possibly 2:2 stoichiometries. The dissociation constant and the changes in dye extinction coefficients on formation of the 1:2 complex, the main complex which forms when Antipyrylazo III is used to study cytoplasmic calcium transients, have been characterized.
mesh_terms: D002118:Calcium; D007202:Indicators and Reagents; D007700:Kinetics; D008433:Mathematics; D009282:Naphthalenesulfonates; D013053:Spectrophotometry
chemical_list: D007202:Indicators and Reagents; D009282:Naphthalenesulfonates; C016238:antipyrylazo III; D002118:Calcium