A group of organic heterocyclic compounds that are comprised of four modified pyrrole subunits connected via methine bridges and form an aromatic macrocyclic structure, which has one or more side chains attached. Many porphyrins are naturally occurring pigments. Porphyrins with metal ions bound to the porphin ring can be cofactors for biological processes, such as oxygen transport by hemes and photosynthesis by chlorophyll.

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, hematoporphyrin, etc; the porphyrins, in combination with iron, form the heme component in biologically significant compounds such as hemoglobin and myoglobin.

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, hematoporphyrin, etc. The porphyrins, in combination with iron, form the heme component in biologically significant compounds such as hemoglobin and myoglobin.