Porphyrinogen

In biochemistry, a porphyrinogen is a member of a class of naturally occurring compounds with a tetrapyrrole core, a macrocycle of four pyrrole rings connected by four methylene bridges. They can be viewed as derived from the parent compound hexahydroporphine by the substitution of various functional groups for hydrogen atoms in the outermost (20-carbon) ring.

Porphyrinogens are intermediates in the biosynthesis of porphyrins, cofactors with a porphine core which are found in many enzymes and proteins including myoglobin, hemoglobin, cytochromes, and chlorophylls.

Porphyrins differ from porphyrinogens by having the four pyrrole rings linked by methine bridges =CH− instead of methylene bridges −CH2−, and by lacking the hydrogen atom in two of the four amine −NH− groups, turning them into imines =N−. In the biosynthesis of porphyrins, the parent porphyrinogen is dehydrogenated by protoporphyrinogen oxidase.

Because of their limited delocalization, porphyrinogens are colorless. Loss of all four central hydrogen atoms in the core yields a tetravalent anion that can act as a ligand to metal cations, creating a coordination compound. Subsequent biosynthetic intermediates en route to porphyrins are deeply colored and often phytotoxic.

Natural porphyrinogens

Porphyrogens that occur in living organisms usually have sidechains replacing some or all of the hydrogen atoms in two outermost carbon atoms of each pyrrole ring (as opposed to the hydrogen atoms in the methylene bridges).

Non-natural porphyrinogens

A variety of synthetic porphyrinogens have been produced and studied in laboratories.