Nonenzymatic reduction of ferric leghemoglobin.

Ferric leghemoglobin isolated from soybean root nodules was reduced nonenzymatically to ferrous leghemoglobin in vitro at pH 5.2 using either 1.0 mM NADH or NADPH as the reductant. In the pH range of 5.2 to 7.0, the highest rates of reduction occurred below pH 6.5 with a maximum rate observed at pH 5.2. Rates of nonenzymatic ferric leghemoglobin reduction above pH 6.5 or at reduced-pyridine nucleotide concentrations below 0.4 mM were insignificant. Oxygen was required for the nonenzymatic reduction. Inhibition of ferric leghemoglobin reduction by superoxide dismutase and catalase indicated that superoxide and hydrogen peroxide may be intermediates in the reaction.