Calcein as a Fluorescent Probe for Ferric Iron

Abstract

The recent use of calcein (CA) as a fluorescent probe for cellular iron has been shown to reflect the nutritional status of iron in mammalian cells (Breuer, W., Epsztejn, S., and Cabantchik, Z. I. (1995) J. Biol. Chem. 270, 24209 -24215). CA was claimed to be a chemosensor for iron(II), to measure the labile iron pool and the concentration of cellular free iron(II). We first study here the thermodynamic and kinetic properties of iron binding by CA. Chelation of a first iron(III) involves one aminodiacetic arm and a phenol.

Solution behaviour of myo-inositol hexakisphosphate in the presence of multivalent cations. Prediction of a neutral pentamagnesium species under cytosolic/nuclear conditions

“…A very high affinity of phytate for Fe(III) and Al(III) has been previously suggested by several workers [12,51]. A ''free Fe(III)'' treatment, similar to that used for divalent cations in relation to EDTA, showed that InsP 6 has an affinity for Fe(III) in the range of that of the multidentate chelator calcein (further discussed below) [52]. We detected only 1:1 complexes with the trivalent cations.…”

“…The fluorescent iron chelator, calcein, is an experimental tool regarded as likely to help resolve this issue [52,60]. We reasoned that if InsP 6 -complexed iron existed in cells, it would necessarily be as Fe(III), for two related reasons.…”

“…Second, Fe(III), unlike Fe(II), has an affinity for InsP 6 that is clearly higher than that of Mg 2+ . With the help of the thermodynamic data for the calcein-Fe(III) equilibrium of Thomas et al [52], we addressed the question of whether any InsP 6 -complexed Fe(III) existing in vivo would be detectable by the use of calcein. For this purpose, the calcein concentration was taken to be 20 lM (corresponding to the cellular concentration of the probe under measuring conditions; [60]), InsP 6 concentration to be the highest reported (60 lM) and Fe(III) concentration was arbitrarily taken as 10 lM.…”

Intracellular Chelation of Iron by Bipyridyl Inhibits DNA Virus Replication

“…The fluorescence of calcein (CA) is quenched upon iron binding; the amount of CA-bound iron is subsequently determined by the amount of CA fluorescence recovered upon addition of a competing, membrane-permeant iron chelator like BIP or SIH. Although there is some controversy about the specificity of CA for Fe 2ϩ versus Fe 3ϩ (45), the data clearly show that chelators like BIP and SIH are Fe 2ϩ -specific indicating that in the cell CA is chelating Fe 2ϩ . This chelatable Fe 2ϩ constitutes ϳ20% of the total iron in both mammalian and yeast cells in culture (30,35).…”

Off–on switchable chemosensor based on rhodamine armed with morpholine moiety

“…Although significant contributions to the development of spectroscopic sensing for Fe 3+ have been made over the last few decades [14][15][16][17], there have been relatively few fluorescent probes for Fe 3+ which showed "off-on" signal. It might be due to its paramagnetic nature which leads to fluorescence quenching.…”