The reaction of ferrous leghemoglobin with hydrogen peroxide to form leghemoglobin(IV)

Abstract

Ferrous leghemoglobin reacts with hydrogen peroxide to form the stable product, leghemoglobin(IV). The reaction follows second order kinetics (k = 2.24 X 10(4) M-1 S-1 at 20 degrees C) and may be regarded as a single-step, two-electron oxidation. Ferric leghemoglobin is not an intermediate. The oxidation state of leghemoglobin(IV) is established by reductive titration with dithionite; 2 eq of dithionite are required to convert 1 mol of leghemoglobin(IV) to ferrous leghemoglobin. An outstanding property of leghemoglobin(IV) is its stability, little change is noted after 12 h at 25 degrees C. Leghemoglobin(IV) differs from the higher oxidation states of other hemoglobins and myoglobins in that it does not react with hydrogen peroxide to form the oxygenated protein.