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 biochemistry roles in living systems, such as hemoglobin and chlorophyll. In these two molecules, in particular, the pyrrole macrocycle ring frames a metal atom, that forms a coordination compound with the pyrroles and plays a central role in the biochemical function of those molecules.
Structure
Linear tetrapyrroles (called
) include:
[ Nomenclature of Tetrapyrroles, Appendix 1. Trivially named porphyrins, chlorins, chlorophylls and bilins, fundamental parents]
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
Cyclic tetrapyrroles having four one-carbon bridges include:
-
Porphin, the simplest tetrapyrrole
-
, including heme, the core of hemoglobin
-
, including those at the core of chlorophyll.
Cyclic tetrapyrroles having three one-carbon bridges and one direct bond between the pyrroles include:
-
, including the cores of , when complexed with a cobalt ion.
File:Heme.svg|Heme group of hemoglobin with a porphin macrocycle.
File:C-3 position Chlorophyll a.svg|The chlorin section of the chlorophyll a molecule. The green box shows a Functional group that varies between chlorophyll types.
File:Cobalamin.svg|Cobalamin structure includes a corrin macrocycle.
The tetrapyrrole portions of the molecules typically act as because of a high degree of conjugation in them. Therefore, these compounds are commonly colored.