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The equilibria in the system V^IVO²⁺-glutathione in aqueous solution were studied in the pH range 2–11 by a combination of pH-potentiometry and spectroscopy (EPR, visible absorption and circular dichroism). The results of the various methods are consistent and the equilibrium model includes the species MLH₃, MLH₂, MLH, ML₂H₂, MLH_–1, and MLH_–2 and several hydrolysis products (where H₄L denotes totally protonated glutathione); individual formation constants and spectra are given. ML₂H₂ is the predominant species at physiological pH. Plausible structures for each stoichiometry are discussed. The related V^IVO²⁺ systems of S-methylglutathione and γ-L-glutamyl-L-cysteinyl ethyl ester were studied by means of the same spectroscopic techniques in order to support the established binding modes for the glutathione complexes. The importance of glutathione and oxidized glutathione in binding V …