Tetrapyrrole

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Tetrapyrroles is a loose term that refers to a class of chemical compounds that contain four pyrrole or pyrrole-like rings. The pyrrole/pyrrole derivatives are linked by (=(CH)- or -CH
2
-
units), in either a linear or a cyclic fashion. Pyrroles are a five-atom ring with four carbon and one nitrogen atoms. Tetrapyrroles are common cofactors in biochemistry and their biosynthesis and degradation feature prominently in the chemistry of life.

Some tetrapyrroles are the active cores of some 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, that forms a coordination compound with the pyrroles and plays a central role in the biochemical function of those molecules.

Structure[edit]

Linear tetrapyrroles (called bilanes) include:[1]

Bilirubin ZZ.png Biliverdin3.svg Phycoerythrobilin.svg Luciferin dinoflagellate.svg Uroporphyrinogen III skeletal.svg
Bilirubin Biliverdin Phycoerythrobilin Dinoflagellate (R = H) and
krill (R = OH) luciferin
uroporphyrinogen III, the only authentic tetrapyrrole shown in this article

Cyclic tetrapyrroles having four one-carbon bridges include:[2]

Cyclic tetrapyrroles having three one-carbon bridges and one direct bond between the pyrroles include:

Heme group of hemoglobin C-3 position Chlorophyll a.svg Cobalamin.svg
Heme group of hemoglobin
with a porphin macrocycle.
The chlorin section of the chlorophyll a molecule.
The green box shows a group that varies between chlorophyll types.
Cobalamin structure includes a corrin macrocycle.

The tetrapyrrole portions of the molecules typically act as chromophores because of a high degree of conjugation in them. Therefore, these compounds are commonly colored.

References[edit]