Dorogi P L, Moss K, Neumann E, Chang H W
Biophys Chem. 1981 Oct;14(2):91-100. doi: 10.1016/0301-4622(81)85010-7.
Stoichiometries, equilibrium constants and optical extinction coefficients of calcium-antipyrylazo III (An) complexing are determined with the analytical method described in article I of this series. Spectrophotometric Ca titrations of An at the wavelengths 595 and 710 nm indicate overall dissociation equilibrium constants for the complexes CaAn, CaAn2 and Ca2An to be 4.5 x 10(-4) M, 1.1 x 10(-8) M2 and 1.5 x 10(-6) M2, respectively, extrapolated to zero ionic strength. Ca titrations of solutions containing An plus acetylcholine receptor protein give clear evidence that An binds to the protein to a large extent in the presence of Ca2+; furthermore, addition of acetylcholine results in release of protein-bound Ca and An. This is the first reported indication that antipyrylazo III binds to biological material and questions the usefulness of this dye as a Ca indicator in biological systems.
采用本系列文章第一篇中所述的分析方法，测定了钙与安替比林偶氮III（An）络合的化学计量比、平衡常数和消光系数。在595和710nm波长下对An进行分光光度法钙滴定，结果表明，络合物CaAn、CaAn2和Ca2An的总解离平衡常数，在外推至零离子强度时分别为4.5×10⁻⁴M、1.1×10⁻⁸M²和1.5×10⁻⁶M²。对含有An加乙酰胆碱受体蛋白的溶液进行钙滴定，结果清楚地表明，在Ca²⁺存在的情况下，An与该蛋白大量结合；此外，加入乙酰胆碱会导致与蛋白结合的钙和An释放。这是首次报道安替比林偶氮III与生物材料结合的迹象，并对这种染料作为生物系统中钙指示剂的实用性提出了质疑。
