Determinations of Uranium(VI) Binding Properties with some Metalloproteins (Transferrin, Albumin, Metallothionein and Ferritin) by Fluorescence Quenching
Résumé
The interactions between uranium and four metalloproteins (Apo-HTf, HSA, MT and Apo-EqSF) were investigated using fluorescence quenching measurements. The combined use of a microplate spectrofluorometer and logarithmic additions of uranium into protein solutions allowed us to define the fluorescence quenching over a wide range of [U]/[Pi] ratios (from 0.05 to 1150) at phy-siologically relevant conditions of pH. Results showed that fluorescence from the four metalloproteins was quenched by UO 2 2+ . Stoichiometry reactions, fluorescence quenching mechanisms and complexing properties of metalloproteins, i.e. binding constants and binding sites densities, were deter-mined using classic fluorescence quenching methods and curve-fitting software (PROSECE). It was demonstrated that in our test conditions, the metalloprotein complexation by uranium could be simulated by two specific sites (L 1 and L 2). Results showed that the U(VI)–Apo-HTf complexation con-stant values (log K 1 =7.7, log K 2 =4.6) were slightly higher than those observed for U(VI)–HSA complex (log K 1 =6.1, log K 2 =4.8), U(VI)–MT complex (log K 1 =6.5, log K 2 =5.6) and U(VI)–Apo-EqsF complex (log K 1 =5.3, log K 2 =3.9). PROSECE fitting studies also showed that the complexing capacities of each protein were different: 550 moles of U(VI) are complexed by Apo-EqSF while only 28, 10 and 5 moles of U(VI) are complexed by Apo-HTf, HSA and MT, respectively.
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