ABSTRACT
The tetrapyrroles are a family of pigments based on a common chemical structure that includes the hemes and chlorophylls. Hemes are cyclic tetrapyrroles that contain iron and are commonly found as the prosthetic group of hemoglobin, myoglobin and the cytochromes. The chlorophylls are modified tetrapyrroles containing magnesium that occur as light-harvesting and reaction center pigments of photosynthesis in plants, algae and photosynthetic bacteria. Hemes 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. Heme biosynthesis takes place primarily in immature erythrocytes, with the remainder occurring in the liver. Several genetic defects in heme biosynthesis have been identified that give rise to the disorders called porphyrias. Heme oxygenase is a member of the cytochrome P450 family of enzymes, and requires NADPH and O2.
