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Keywords:

fluorescence titration, fluorescent ion indicator, decay time analysis, mag-fura-2, sbfo, aptra-btc, state dissociation-constant, decay surfaces, intracellular mg2+, global analysis, free magnesium, Science & Technology, Life Sciences & Biomedicine, Physical Sciences, Biochemical Research Methods, Chemistry, Analytical, Chemistry, Physical, Biochemistry & Molecular Biology, Chemistry, Mag-fura-2, SBFO, APTRA-BTC, STATE DISSOCIATION-CONSTANT, DECAY SURFACES, INTRACELLULAR MG2+, GLOBAL ANALYSIS, FREE MAGNESIUM, 0301 Analytical Chemistry, 0306 Physical Chemistry (incl. Structural), Chemical Physics, 3406 Physical chemistry

Abstract:

A test based on time-resolved fluorescence experiments (Anal. Biochem.245, 28-37, 1997) allows one to assess the interference of the excited-state association with the fluorimetric determination of the ground-state dissociation constant K-d Of fluorescent ion:indicator complexes. If an inflection point occurs in the plot of the fluorescence signal vs - log[ion] in the ion concentration range where both decay times are invariant, this inflection point can be associated with the correct K-d Here we apply this test to the fluorescent ion indicators SBFO (for Na+), Mag-fura-2 (for Mg2+), and APTRA-BTC (for Ca2+). In all three cases the decay times are invariant in the concentration ranges of the respective ions where the fluorescence titrations show unique inflection points, indicating that the fluorimetrically determined K-d values are the true K-d values.