A reinvestigation of turacin, the copper porphyrin pigment of certain birds belonging to the musophagidae

Abstract

The first careful examination of the red pigment occurring in the wing feathers of certain turacos, African birds belonging to the family Musophagidae, N. O. Scansores, was made by Church in 1869, and he it was who proposed the name "Turacin" for this pigment. His observations were extended in 1892, and since then the subject has received study at the hands of Laidlaw (1904) and Fischer and his associates. Fischer and Hilger (1924) reported that turacin was identical with the copper complex of uroporphyrin I. The system of nomenclature developed by Fischer is based upon differences in regard to the positions of the substituent groups upon the pyrrole nuclei comprising the porphine ring system. In the case of the aetio-porphyrins, there are present four methyl and four ethyl groups which may be arranged in such a manner that four possible isomeric aetioporphyrins result. Fischer has named these aetioporphyrins I, II, III and IV, and each may be regarded as the parent substance of a potential series of porphyrin pigments. Replacement of the four ethyl groups by propionic acid residues gives rise to the coproporphyrins which are thus tetracarboxylic acids. When, in addition, four acetic acid residues take the place of the methyl groups, the uroporphyrins result, possessing eight carboxyl groups in the molecule. These relationships are illustrated by the formulae for coproporphyrins I and III, and for uroporphyrin I, reproduced in the accompanying figures (see fig. 1-3).