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}}