The porphyrins and their closely related molecules are essential to all plants and animals. An iron porphyrin, called heme, is the portion of hemoglobin that carries oxygen from the lungs to our body's cells. The heme of another protein, myoglobin, carries oxygen within muscle cells. Other iron porphyrins in the cytochromes transport electrons in metabolic processes. A closely related type of molecule is chlorophyll, a key component of the photosynthetic process.

A porphyrin is a macrocyclic (large cycle) molecule that is made up of four smaller pyrrolenine rings. Each pyrrolenine ring is made up of a nitrogen atom and four carbon atoms. In the porphyrin ring, they are linked to each other by a carbon atom that bridges from the carbon atom nearest the nitrogen atom of one ring to the carbon atom nearest the nitrogen atom of the next ring (called the alpha carbon). The porphyrin ring...