Tetrapyrroles are a class of chemical compounds that contain four pyrrole or pyrrole-like rings. The pyrrole/pyrrole derivatives are linked by (methine group| or methylene bridge| units), in either a linear or a cyclic fashion. Pyrroles are a five-atom ring with four carbon atoms and one nitrogen atom. Tetrapyrroles are common cofactors in biochemistry and their biosynthesis and degradation feature prominently in the chemistry of life.
Some tetrapyrroles form the active core of compounds with crucial biochemical roles in living systems, such as hemoglobin and chlorophyll. In these two molecules, in particular, the pyrrole macrocycle ring frames a metal atom, which forms a coordination compound with the pyrroles and plays a central role in the biochemical function of those molecules.
Structure
Linear tetrapyrroles (called bilanes) include:
- Heme breakdown products (e.g., bilirubin, biliverdin)
- Phycobilins (found in cyanobacteria)
- Luciferins as found in dinoflagellates and euphausiid shrimps (krill)
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File:Bilirubin ZZ.png|Bilirubin
File:Biliverdin3.svg|Biliverdin
File:Phycoerythrobilin.svg|Phycoerythrobilin
File:Luciferin dinoflagellate.svg|Dinoflagellate (R=H) and krill (R=OH) luciferin
File:Uroporphyrinogen III skeletal.svg|uroporphyrinogen III, an authentic tetrapyrrole
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Cyclic tetrapyrroles having four one-carbon bridges include: