Biliverdin

Biliverdin is a green tetrapyrrole pigment formed during heme breakdown. Biliverdin reductase converts it into bilirubin.

Heme oxygenase: Heme oxygenase enzymes cleave heme, releasing biliverdin, carbon monoxide, and iron. This enzyme family produces biliverdin by opening heme’s porphyrin ring.
Tetrapyrrole: A tetrapyrrole is a molecule built from four pyrrole rings linked into a larger framework. Biliverdin belongs to this structural family, though its ring framework is open.
Jaundice: Jaundice is yellowing of the skin and eyes caused by elevated bilirubin in tissues. Biliverdin is the immediate precursor to the pigment that accumulates in jaundice.
Iron recycling: Iron recycling is the recovery and reuse of iron released from molecules such as heme. Heme oxygenase releases iron while producing biliverdin, coupling pigment formation to iron recovery.
Biliverdin reductase: Biliverdin reductase is an enzyme that reduces biliverdin to bilirubin using NADPH or NADH. It carries out the next step in biliverdin’s conversion to bilirubin.
Porphyrin: Porphyrins are cyclic tetrapyrrole compounds that bind metal ions at their center. Heme’s porphyrin framework is opened during the reaction that forms biliverdin.
Bile pigment: Bile pigments are colored products of heme breakdown, including biliverdin and bilirubin. Biliverdin is one member of this family of heme-derived pigments.
Heme catabolism: Heme catabolism is the enzymatic breakdown of heme into products that can be excreted or reused. Biliverdin is a short-lived intermediate in this larger disposal pathway.
Bilirubin: Bilirubin is a yellow tetrapyrrole pigment formed by reduction of biliverdin and processed by the liver. This is the product formed when biliverdin reductase reduces the green pigment.
Pyrrole: Pyrrole is a five-membered aromatic ring containing one nitrogen atom. Four pyrrole-derived units form the backbone of biliverdin.

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