HMOX2 is microsomal enzyme that cleave heme ring at the alpha methane bridge to produce the antioxidant biliverdin, inorganic iron and carbon monoxide. Biliverdin is subsequently converted to bilirubin by bilibverdin reductase. This protein appears to be constitutively expressed in mammalian tissues. HMOX2 is involved in the production of carbon monoxide (CO) in brain, where CO is thought to act as a neurotransmitter.