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Biophysical Journal 36: 607-621 (1981)
© 1981 the Biophysical Society

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Stoichiometry of the reactions of calcium with the metallochromic indicator dyes antipyrylazo III and arsenazo III.

E Ríos and M F Schneider

ABSTRACT

A method for determining the stoichiometry of one-product reactions involving a metal ion and an organic ligand is presented and applied to the reactions of calcium and magnesium with the metallochromic dyes Antipyrylazo III and Arsenazo III. The method consists of fitting titration data, obtained in solutions buffered for the metal, with theoretical functions that include: (a) the dependence of product concentration on the concentration of both reactants, (b) the relationship between metal ion concentration and total amount added in the presence of the buffer, and (c) a correction for the amount of metal ion that binds to the organic ligand. It is shown that the products of the reactions of Antipyrylazo III with calcium and magnesium are CaD2 and MgD, respectively. The product formed between calcium and Arsenazo III at [Ca2+] over 20 microM is CaD2, other products accumulating at lower [Ca2+]. The kinetics of the Antipyrylazo III:Ca reaction are rapid under conditions in which this dye has been applied to measure calcium transients in skeletal muscle fibers. The present results provide a calibration for previous studies with Antipyrylazo III in muscle fibers.




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G. Pizarro and E. Rios
How Source Content Determines Intracellular Ca2+ Release Kinetics. Simultaneous Measurement of [Ca2+] Transients and [H+] Displacement in Skeletal Muscle
J. Gen. Physiol., August 30, 2004; 124(3): 239 - 258.
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Copyright © 1981 by the Biophysical Society.