Hemoproteins oxidative attack

In addition to structural changes of this kind occurring, when the hemoproteins take part in oxidation-reduction reactions there is the further possibility of irreversible oxidative attack on the porphyrin ring itself. Lemberg, Legge, and Lockwood (27) have studied this process in the case of hemoglobin and have named the oxidation product chole-globin the precise nature of this compound has not yet been established. 

When the taurine chloramine uptake rate exceeds the rate of NADPH-dependent regeneration of GSH, there is a net loss of cellular GSH level, causing protein-thiol oxidation, ATP loss, and disruption of cellular metabolism. Heme moieties are the other target of chloramine attack on cellular constituents. Oxidation of hemoglobin to methemoglobin (and other hemoproteins to their oxidized derivatives) occurs at 10-fold excess of chloramine taurine molar concentration compared... 

When free peroxidases or catalase react with hydroperoxides, stable green substances, called compounds I and II, are formed they have absorption spectra of yr-cation-radical type [Blumberg (7), Brill (16)]. This has been taken as evidence that stable Fem porphyrin cation radicals are formed by peroxide oxidation in these particular heme proteins [Borg (10), Dolphin (51)]. It is not known why the hydrogen peroxide does not attack the porphyrin ring, as is normal with hemoproteins, nor is it certain whether this radical formation has any biological implication. 

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