A group of compounds containing the porphin structure, four pyrrole rings connected by methine bridges in a cyclic configuration to which a variety of side chains are attached. The nature of the side chain is indicated by a prefix, as uroporphyrin, haematoporphyrin, etc. The porphyrins, in combination with iron, form the haem component in biologically significant compounds such as haemoglobin and myoglobin.

(12 Dec 1998)