Porphyria in animals

Porphyrins are found to be widely, although erratically, distributed throughout the animal kingdom. It would indeed have been surprising had it been otherwise since the tetrapyrrole ring system is a key material used in hemoproteins and essential for all biologic oxidative metabolism in the fabric of life. Those anaerobes, which possess no cytochromes or other hemoproteins, may be regarded as degenerate forms in which this biosynthetic ability has been lost. The porphyrins are stable chemical materials that have been detected in fossil shells from the post-Pleistocine and upper-Eocene deposits and are thus many millions of years old.^1,2 In the lower phyla, the black slug, Arion, contains great quantities of uroporphyrin. Among the higher forms of animal life, the group of birds known as the Turacos or plantain-eaters are unique in having utilized the copper complex of uroporphyrin III, called turacin,³ for the deep red areas of pigmentation in their flight feathers (Fig. 1) although there seems to be nothing otherwise unusual about the porphyrin metabolism of these birds.⁴ Other birds also have porphyrins in their feathers and down^5–7 and porphyrins are used in the coloration of eggs. Among the mammals, a few genera appear normally to produce much more porphyrin than others and these belong to the family of rodents. The rat excretes a relatively large quantity of protoporphyrin, which arises by synthesis in Harder's glands.⁸