porphyrin

n. substance found in the protoplasm of plants and animals

A porphyrin is a heterocyclic macrocycle derived from four pyrrole-like subunits interconnected via their α carbon atoms via methine bridges (=CH-). The macrocycle, therefore, is a highly conjugated system, and is consequently deeply coloured—the name porphyrin comes from a Greek word for purple. The macrocycle has 22 pi electrons. The parent porphyrin is porphine, and substituted porphines are called porphyrins. Many porphyrins occur in nature, such as in green leaves and red blood cells, and in bio-inspired synthetic catalysts and devices.
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Porphyrin /por·phy·rin/ any of a group of compounds containing the porphin structure to which a variety of side chains are attached, the nature of [more]Porphyrin - Community and Resources

Noun
1. any of various pigments distributed widely in living tissues
(hypernym) pigment

n. porphyrin, substance found in the protoplasm of plants and animals