Measurement of free Zn2+ ion concentration with the fluorescent probe mag-fura-2 (furaptra)

Abstract

The fluorescent probe mag-fura-2, previously used to measure [Mg2+], can also be used to measure [Zn2+]. The peak in the excitation spectrum occurs at 323 nm for Zn2+, compared with 335 nm for Ca2+ and Mg2+. This allows simultaneous measurements of [Zn2+] and either [Ca2+] or [Mg2+], by using 3 excitations wavelengths. The dissociation constant for Zn2+ is 20 nM at pH 7.0–7.8, ionic strength 0.15 and 37°C. This allows [Zn2+] to be measured in the range from 0.5 nM to 1 μM. Mag-fura-2 was used to measure [Zn2+] in Zn2+/albumin and Zn2+/histidine mixtures in a physiological buffer at 37°C and pH 7.4. The data obtained enable one to formulate Zn2+-buffers for the 1 to 100 nM Zn2+ range.