Activated oxygen species in the oxidation of glutathione - A kinetic study

The generation of the superoxide ion in the oxidation of glutathione (GSH) by molecular oxygen has been demonstrated in the absence and in the presence of a catalytic amount of copper ion. An effort has been made to quantify the production of superoxide ion by an NMR method utilising Cu,Zn superoxide dismutase and to correlate it to the reaction mechanism. The oxidation process is first-order with respect to GSH and molecular oxygen, the ratio Delta[GSH]/Delta[O-2] being 4.0 +/- 0.1. The rate of superoxide ion generation is independent of the GSH concentration and increases linearly with the O-2 concentration. The addition of Cu2+ increases the rate of GSH oxidation and of O-2 consumption. Also in this case the oxidation process is first-order with respect to GSH and O-2, while a saturation effect with respect to Cu2+ is observed. A kinetic scheme involving the formation of a short-living charge-transfer complex between GSH and oxygen is proposed to explain the experimental data.