Heme oxygenase 3568423 191764640 2008-02-16T01:12:59Z Dycedarg 1095145 Repairing link to disambiguation page - [[Wikipedia:Disambiguation pages with links|You can help!]] using [[Project:AutoWikiBrowser|AWB]] '''Heme oxygenase''' (HO) is an [[enzyme]] that [[catalyst|catalyzes]] the degradation of [[heme]]. This produces [[biliverdin]], [[iron]], and [[carbon monoxide]]. ==Reaction== Heme oxygenase cleaves the heme ring at the alpha-methene bridge to form either biliverdin or, if the heme is still attached to a [[globin]], [[verdoglobin]]. Biliverdin is subsequently converted to [[bilirubin]] by [[biliverdin reductase]]. The reaction occurs as follows: ::{{chem|Heme + 3 AH|2| + 3 O|2| → biliverdin + Fe<sup>2+</sup> + CO + 3A + 3 H|2|O}} <gallery> Image:Heme.svg |[[heme]] Image:Biliverdin.png|[[biliverdin]] </gallery> This reaction can occur in virtually every [[cell (biology)|cell]]; the classic example is the formation of a [[bruise]], which goes through different colors as it gradually heals: red heme to green biliverdin to yellow bilirubin. Under normal physiological conditions, the activity of heme oxygenase is highest in the [[spleen]], where old [[erythrocyte]]s are sequestrated and destroyed. ==Isoforms== There are three known [[isoform]]s of heme oxygenase. [[HMOX1|Heme oxygenase 1 (HO-1)]] is an inducible isoform in response to stress such as oxidative stress, [[Hypoxia (medical)|hypoxia]], [[heavy metal]]s, [[cytokine]]s, etc. Heme oxygenase 2 (HO-2) is a constitutive isoform which is expressed under homeostatic conditions. Both HO-1 and HO-2 are ubiquitously expressed and catalytically active. A third heme oxygenase (HO-3) is not catalytically active, but is thought to work in oxygen sensing. ==See also== * [[HMOX1]] ==External links== * {{MeshName|Heme+Oxygenase}} * {{EC number|1.14.99.3}} {{Dioxygenases}} {{Porphyrin metabolism enzymes}} [[Category:Enzymes]] {{enzyme-stub}}