Glutathione-dependent conversion of ferryl leghaemoglobin into the ferric form: a potential protective process in soybean (Glycine max) root nodules

GSH is able to reduce soybean (Glycine max) ferryl-leghaemoglobin [Lb(IV)] formed by the reaction of ferric or ferrous Lb with H2O2; in both cases, ferric Lb is obtained and GSH is incapable of reducing ferric Lb to ferrous Lb. Furthermore, the addition of GSH before H2O2 to ferric Lb prevents side reactions which lead to a species whose spectrum differs markedly from that of Lb(IV). These reactions are likely to occur in vivo, as high GSH concentrations have been detected in soybean nodules. The GSH-dependent reduction of Lb(IV) is associated with the oxidation of GSH to GSSG. E.s.r. experiments show that the glutathione thiyl radical (GS.) is formed during this reaction. In the case of ferric Lb, both ferryl Lb and a globin-derived radical previously described appear to be involved in the formation of GS. Both of these processes may be protective and can help account for the exclusive presence of ferrous (oxygenated or not) Lb in functioning nodules.