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PHOTOPHYSICS OF THE FLUORESCENT Ca 2+ INDICATOR QUIN‐2
Author(s) -
Bergh Viviane Van den,
Boens Noël,
Schryver Frans C. De,
Gallay Jacques,
Vincent Michel
Publication year - 1995
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1995.tb02342.x
Subject(s) - excited state , reaction rate constant , chemistry , dissociation constant , fluorescence , analytical chemistry (journal) , dissociation (chemistry) , aqueous solution , kinetics , atomic physics , chromatography , physics , biochemistry , receptor , quantum mechanics
The photophysics of the complex forming reaction between Quin‐2 and Ca 2+ were investigated using steady‐state and time‐resolved fluorescence measurements. The fluorescence decay traces were analyzed with global compartmental analysis yielding the following values for the rate constants at room temperature in aqueous solution with EGTA as Ca 2+ buffer: k 01 = 8.6 times 10 8 s −1 , k 21 = 1 times 10 11 M −1 s −1 , k 02 = 8.8 times 10 7 s −1 , k 12 = 4 times 10 4 s −1 . k 01 and k 02 denote the respective deactivation rate constants of the Ca 2+ free and bound forms of Quin‐2 in the excited state. The constant k 21 represents the second‐order rate constant of binding of Ca 2+ and Quin‐2 in the excited state while k 12 is the first‐order rate constant of dissociation of the excited Ca 2+ :Quin‐2 complex. From the estimated values of k 12 and k 21 the dissociation constant K d * in the excited state was calculated. It was found that pK d * (6.4) is slightly smaller than pK d (7.2). There was no interference of the excited‐state complex forming reaction with the determination of K d . Intracellular Ca 2+ concentrations can thus accurately be determined from fluorometric measurements using Quin‐2 as Ca 2+ indicator.