Hæmoglobin – Methæmoglobin Mixtures

Abstract

WE¹ have recently had an opportunity of confirming, in a case of familial methæmoglobinæmia, the shift to the left in the oxygen dissociation curve of hæmoglobin which Darling and Roughton² found in hæmoglobin – methæmoglobin mixtures. They suggest that the shift in the curve may be explained by the existence of intermediate compounds, the affinity of which for oxygen is greater than that of hæmoglobin. On this assumption, the formation of methæmoglobin from hæmoglobin does not take place in a single step; but the four iron atoms of the hæmoglobin molecule may be oxidized separately and successively. If the iron in the hæmoglobin (or oxyhæmoglobin) molecule is represented as (Fe⁺⁺)₄, the iron in the intermediate mixed molecules would be (Fe⁺⁺⁺) (Fe⁺⁺)₃, (Fe⁺⁺⁺)₂ (Fe⁺⁺)₂, (Fe⁺⁺⁺)₃ (Fe⁺⁺), and that in methæmoglobin itself (Fe⁺⁺⁺)₄. As the shift in the dissociation curve is fairly large, it is evident that quite appreciable amounts of the intermediate compounds would be present in methæmoglobin – hæmoglobin mixtures, and might afford spectroscopic evidence of their presence. Apart from its theoretical interest, the question is of some practical importance, for alterations in the absorption spectrum due to this cause Would necessitate modifications in the estimation of blood methæmoglobin made by optical methods, for example, that of Evelyn and Malloy³.