Porphyrin vs. Heme — What's the Difference?

Porphyrins ( POR-fər-in) are a group of heterocyclic macrocycle organic compounds, composed of four modified pyrrole subunits interconnected at their α carbon atoms via methine bridges (=CH−). The parent of porphyrin is porphine, a rare chemical compound of exclusively theoretical interest.

Heme, or haem (spelling differences) is a substance precursive to hemoglobin, which is necessary to bind oxygen in the bloodstream. Heme is biosynthesized in both the bone marrow and the liver.In microbiological terms, heme is coordination complex "consisting of an iron ion coordinated to a porphyrin acting as a tetradentate ligand, and to one or two axial ligands." The definition is loose, and many depictions omit the axial ligands.

Any of various organic compounds containing four pyrrole rings, occurring universally in protoplasm, and functioning as a metal-binding cofactor in hemoglobin, chlorophyll, and certain enzymes.

A deep red, iron-containing compound, C34H32FeN4O4, that constitutes the nonprotein component of hemoglobin and certain other proteins.

(organic compound) Any of a class of heterocyclic compounds containing pyrrole rings arranged in a square or other similar shape; they are important in biochemistry in a form with a metal atom in the central cavity (hemoglobin with iron, chlorophyll with magnesium, etc.).

(biochemistry) The component of hemoglobin (and other hemoproteins) responsible for binding oxygen. It consists of an iron ion that binds oxygen and a porphyrin ring that binds the globin molecules; one molecule binds one molecule of oxygen.

Any of various pigments distributed widely in living tissues

A complex red organic pigment containing iron and other atoms to which oxygen binds