Tetrapyrrole

Tetrapyrroles are compounds containing four pyrrole rings. With the exception of corrin, the four pyrrole rings are interconnected through one-carbon (methine or methylene) bridges, either in a linear or cyclic fashion.

Linear tetrapyrroles, using three one-carbon bridges, include:
 * Bilanes (e.g. bilirubin)
 * Phycobilins (found in cyanobacteria)

Cyclic tetrapyrroles, using four one-carbon bridges, include:
 * Porphyrins (e.g. heme)
 * Chlorophylls

Corrins are cyclic tetrapyrroles that have replaced one of the conventional methine bridges with a direct interpyrrole bond.

テトラピロール 四吡咯