The suppression of iron release from activated myoglobin by physiological electron donors and by desferrioxamine

Interactions between ferrimyoglobin and hydrogen peroxide have been postulated to lead to the formation of activated ferryl myoglobin. In such systems hydroxyl radical formation has also been demonstrated by its ability to degrade deoxyribose subsequent to the release of iron from the porphyrin ring of the myoglobin. We have investigated the potential for ferrylmyoglobin formation and for iron release from ferrylmyoglobin exposed to hydrogen peroxide; the modulation of the stability of the haem group by membranes and in the presence of desferrioxamine and ascorbate have also been assessed. The results show that iron release from ferrimyoglobin activated by hydrogen peroxide is suppressed in the presence of membranes, apparently by the reduction of the ferryl myoglobin species, and lipid peroxidation occurs. In the presence of desferrioxamine, formation of the ferrylmyoglobin species is suppressed by the electron donating properties of the trihydroxamate moiety, which also functions as a chain-breaking antioxidant when added to peroxidising membranes. The physiological antioxidant ascorbate not only suppresses the formation of the ferryl myoglobin species under the conditions described here, but also reduces the myoglobin iron to the iron II state.