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17 August 1994 Photophysical study of the Ca2+ indicator Fura-2 and the K+ indicator PBFI
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The fluorescent indicators Fura-2 and PBFI are widely used for the determination of intracellular concentrations of Ca2+ and K+, respectively. To investigate the complex forming reaction between Fura-2 and Ca2+, and between PBFI and K+ in the ground and excited states, steady-state and time-resolved measurements were performed. The fluorescence decay surfaces were analyzed with global compartmental analysis yielding the following values for the rate constants at room temperature in aqueous solution: (1) for Fura-2: k01 equals 1.2 X 109 s-1, k21 equals 1.0 X 1011 M-1x-1, k02 equals 5.5 X 108s-1, k12 equals 2.2 X 107s-1 (2) for PBFI: k01 equals 1.1 X 109s-1, k21 equals 2.7 X 108M-1s-1, k02 equals 1.8 X 109s-1, k12 equals 1.4 X 109s-1 k01 and k02 denote the deactivation rate constants of the free and bound forms of the indicator, respectively k21 represents the bimolecular rate constant of binding of the cation by the indicator whereas k12 is the rate constant of dissociation of the cation:indicator complex. For both probes the effect of the excited-state reaction can be neglected in the determination of Kd and/or the ion concentration.
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Viviane Van den Bergh, Katrien Meuwis, Noel Boens, Frans C. De Schryver, Michel Vincent, Jacques Gallay, and Marcel Ameloot "Photophysical study of the Ca2+ indicator Fura-2 and the K+ indicator PBFI", Proc. SPIE 2137, Time-Resolved Laser Spectroscopy in Biochemistry IV, (17 August 1994); doi: 10.1117/12.182705;

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