Verdohaem and ‘verdoglobins’

Abstract

Verdohaem cannot be reconverted into porphyrin derivatives. It is converted into biliverdin by a hydrolytic process without oxidation. Verdohaem contains the 33 carbon atoms of the bile pigments, not the 34 of haem. In contrast to verdohaem, green haemoglobins (choleglobin, pseudohaemoglobin, cruoralbin) are reconvertible to porphyrin derivatives, though not as readily as sulphhaemoglobin. Heating with alkaline solutions containing dithionite converts them to red haemochromogens, derived from ether-insoluble porphyrins. The myeloperoxidase of leucocytes gives the same reaction. By energetic treatment with mineral acids, the green haemoglobins yield ether-insoluble porphyrin. Their prosthetic group still contains the closed porphyrin ring and 34 carbon atoms. It is thus quite different from verdohaem, and the name ‘verdoglobins’ for the green haemoglobins is misleading. Protein-free pseudohaem compounds can be obtained by treating alkaline solutions of haemins with dithionite and hydrogen peroxide in the presence of cyanide. After removal of cyanide by dialysis, pseudohaematin can be coupled with native globin to a compound with the absorption spectrum of choleglobin, which does not yield biliverdin with acids. It is concluded that the biliverdin which is obtained by the action of acid on choleglobin solutions is not derived from the main component of pseudohaem type, but from an admixture of verdoglobin. Cholehaem (or pseudohaem) compounds are precursors of verdohaem compounds, to which they can be oxidized. Another intermediate, spectroscopically similar to verdohaem, but reconvertible into porphyrin derivatives, like pseudohaem, can be observed, particularly in the meso series. The formation of choleglobin, of pseudohaemoglobin, and of protein-free pseudohaems from the cyanide compounds of haematins is accompanied by by-reactions, the former two reactions by a condensation with cysteine-sulphur from globin, the latter by the introduction of sulphur-containing groups derived from dithionite. Such by-reactions do not occur in the bile pigment formation in vivo and limit the amount of bile pigment obtainable from haemoglobin in vitro .