Glutathione (GSH) is a natural antioxidant found in the human body that has a variety of important functions including the reduction of harmful free radicals that cause oxidative stress, cell damage, and cancer. In the cytosol of cells, there exists a low concentration of iron called the “labile iron pool” which hasn’t been chemically well characterized, although studies have suggested that GSH is one likely candidate for stabilizing the cellular “free” iron. Here, we have characterized the association between GSH, ferrous, copper, and zinc ions using isothermal titration calorimetry in terms of their binding affinity (Ka), binding stoichiometry (n), enthalpy change (ΔH°), entropy change (ΔS°), and Gibbs free energy change (ΔG°). The data showed a range of binding affinities extending from ~104 M–1 for Zn2+, to ~105 M–1 for Fe2+, and ~106 M–1 for Cu2+. The binding stoichiometry was shown to vary between 0.3 and 0.5 metal ion per GSH molecule, suggesting the formation of different structures of the GSH:metal ion complexes. With the exception of Zn2+, ΔH° values for Fe2+ and Cu2+ binding to GSH were negative, suggesting exothermic binding events. The negative ΔS° values were mainly attributed to the conformational changes resulting from the conversion of flexible metal-free GSH molecules to a more rigid structure upon complexation with the metal ion.

Thermodynamics of glutathione binding to Fe(II), Cu(II), and Zn(II): An isothermal titration calorimetry study

256th National Meeting (2018)

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