ABSTRACT
The tetrapyrroles are a family of pigments based on a common chemical structure that includes the hemes and chlorophylls. The red heme and green chlorophyll pigments, so important in the energy-producing mechanisms of respiration and photosynthesis, are both members of the family of pigments called tetrapyrroles. Hemes (Fig. 1a) are a diverse group of tetrapyrrole pigments, being present as the prosthetic group of both the globins and the cytochromes and the cytochrome P450s that are used in detoxification reactions. The chlorophylls are also a diverse family of pigments, existing in different forms in photosynthetic bacteria, algae and higher plants. Four porphobilinogens then condense head-to-tail in a reaction catalyzed by porphobilinogen deaminase to form a linear tetrapyrrole. Bile pigments exist in both the plant and animal kingdoms, and are formed by breakdown of the cyclic tetrapyrrole structure of heme.
