Photophysics of Mag-fura-2: a fluorescent indicator for intracellular Mg 2+

Abstract

Mag-fura-2 is the first commercial fluorescent indicator for the determination of intracellular Mg 2+ concentrations. To investigate the reversible reaction of Mg 2+ with this indicator in the ground and excited states, steady-state and time-resolved fluorescence measurements were done. The following values of the rate constants at room temperature in aqueous solution at pH 7.2 were recovered by global compartmental analysis from the fluorescence decay surface: k 01=4×10 8 s −1, k 21=8×10 8 M −1 s −1, k 02=6×10 8 s −1, k 12=4×10 7 s −1. k 01 and k 02 denote the deactivation rate constants of the Mg 2+-free and bound forms of the indicator in the excited state, k 21 the second-order rate constant of association of Mg 2+ with Mag-fura-2 in the excited state, and k 12 is the first-order rate constant of dissociation of the excited Mg 2+:indicator complex. The excited-state complex-forming reaction does not interfere with the fluorimetric determination of K d.