Haemoglobin and myoglobin as inhibitors of hydroxyl radical generation in a model system of "iron redox" cycle.

Methionine was oxidized to ethylene by an "Iron Redox" system containing H2O2, Fe-EDTA and ascorbate, generating hydroxyl radicals or another species of similar reactivity. Oxy or met forms of haemoglobin and myoglobin were found to inhibit methionine oxidation. Methionine oxidation was elevated in the "Iron Redox" system by increasing ascorbic acid concentration. However, in the presence of metmyoglobin or methaemoglobin, the increases in ascorbic acid did not lower the haemproteins' inhibitory effects but rather increased them. The pro-oxidative or anti-oxidative activities of haemproteins in biological oxidative reactions seem to be dependent on compartmentalization and on the presence and concentrations of reducing compounds and H2O2.