Tetrapyrroles are a class of chemical compounds containing four pyrrole rings held together by direct covalent bonds or by one-carbon bridges (=(CH)- or -CH
2- units), in either a linear or a cyclic fashion.
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 macroring frames a metal atom, that forms a coordination compound with the pyrroles and plays a central role in the biochemical function of those molecules.
Linear tetrapyrroles (called bilanes) include:
Cyclic tetrapyrroles, using four one-carbon bridges, include: