Generation of hydroxyl radicals by soybean nodule leghaemoglobin.

Leghaemoglobin, a protein present in root nodules of soybean (Glycine max (L.) Merr.), generates the highly reactive hydroxyl radical (·OH) upon incubation with hydrogen peroxide (H2O2). The H2O2 appears to cause breakdown of the haem, releasing iron ions that convert H2O2 into ·OH outside the protein. Oxyleghaemoglobin (oxygenated ferrous protein) is more sensitive to attack by H2O2 than is metleghaemoglobin (ferric protein). The possibility of oxyleghaemoglobin breakdown by H2O2 and formation of damaging ·OH may explain why the root nodule is equipped with iron-storage proteins and enzymes that can remove H2O2.