Heme oxygenase !

Heme oxygenase breaks the heme ring, releasing biliverdin, iron and carbon monoxide.

Updated 2026-11-01

Loading the 3D model…

Key facts

Heme + 3 O₂ + electrons from NADPH → biliverdin IXα + Fe²⁺ + CO.
It is anchored to the endoplasmic reticulum and gets its electrons from NADPH–cytochrome P450 reductase.
It cuts the α bridge of the ring; it is the main source of endogenous CO (that is why exhaled CO rises in hemolysis).
HO-1 is abundant in spleen and liver macrophages; HO-2 is constitutive in brain and testis.

HO-1 is induced by its substrate (heme), oxidative stress, hypoxia, heavy metals and inflammation (via Nrf2).

Its products are protective: biliverdin and bilirubin are antioxidants, and CO has vasodilating and anti-inflammatory effects.
HO-1 deficiency (very rare) causes severe hemolysis, inflammation and endothelial damage.
In hemolysis it works harder: more unconjugated bilirubin, more exhaled CO and more recycled iron.

Think of the answer, then tap the question to see it.

What are the three products of heme oxygenase?

Biliverdin, Fe²⁺ and carbon monoxide.

Why does exhaled CO rise in hemolysis?

Because more heme is broken down, and heme oxygenase is the body's main source of CO.

Which heme oxygenase isoform is inducible?

HO-1, induced by heme, oxidative stress and inflammation; HO-2 is constitutive.

Educational information, not medical advice. For any symptom, see a health professional.

Sources: HMOX1: Heme oxygenase 1 (human) (UniProt, 2026); 1N45: X-RAY CRYSTAL STRUCTURE OF HUMAN HEME OXYGENASE-1 (HO-1) IN COMPLEX WITH ITS SUBSTRATE HEME (RCSB Protein Data Bank, 2026); Reactome | Heme degradation (Reactome, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake

Representative model, for educational purposes only.