The combination between methæmoglobin and peroxides : hydrogen peroxide and ethyl hydroperoxide

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Abstract
Methemoglobin containing little or no catalase was prepared from crystalline horse hemoglobin. Solutions of acid methemoglobin, on addition of H2O2, turn from brown to red, and the characteristic absorption spectrum of acid methemoglobin is replaced by 2 diffuse bands at 589 mu and 545 mu. This change of color and absorption spectrum is due to the formation of a real compound between H2O2 and methemoglobin. The H2O2-methemoglobin is analogous to the compounds formed between methemoglobin and KCN, KF, H2S, and NaN3, from all of which unmodified hemoglobin can be recovered. By spectroscopic and manometric methods it was found that the formation of H2O2-methemoglobin requires 1 molecule of the H2O2 per atom of iron of methemoglobin. Ethyl hydro-peroxide (C2H5OOH) combines with methemoglobin, forming a compound similar in every respect to H2O2-methemoglobin. The formation of ethyl hydroperoxide-methemoglobin also requires 1 molecule of ethyl hydro-peroxide per atom of iron of methemoglobin. Both peroxides (H2O2 and C2H5OOH) oxidize hemoglobin to methemoglobin. While ethyl hydroperoxide does so even in the presence of catalase, H2O2 acts only on hemoglobin more or less free from catalase or when the activity of the latter is inhibited by KCN or NaN3. Both peroxide-methemoglobin compounds are unstable and on standing even at room temp. revert to acid methemoglobin. During this decomposition, H2O2 is not split into molecular oxygen and water and both peroxides seem to be utilized in a true oxidation reaction such as is promoted by peroxidase.

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