Figure 4

ESI-MS spectra of interacting systems, involving the Cu(II) complexes, L-cysteine, and reduced glutathione. ESI-MS spectrum of the mixture of physiological levels of cysteine (290 μM) and glutathione (6 μM) in 50 mM ammonium acetate in water (a; red line); the interacting system containing cysteine (290 μM) + glutathione (6 μM) + complex 5 (1 μM) in the mixture of 50 mM ammonium acetate and methanol (1:1, v/v) immediately after the preparation (b; green line); the interacting system containing cysteine (290 μM) + glutathione (6 μM) + complex 5 (7 μM) in the mixture of 50 mM ammonium acetate and methanol (1 : 1, v/v) immediately after the preparation (c; blue line), both (i.e. lines b and c) showing the appearance of the specific ions, connected either with the oxidative mechanism of the interaction or the ligand-exchange mechanism (for more details See Section Interactions with sulfur-containing biomolecules).