|PROSITE documentation PDOC00512|
Heme oxygenase (EC 18.104.22.168) (HO)  is the microsomal enzyme that, in animals, carries out the oxidation of heme, it cleaves the heme ring at the α methene bridge to form biliverdin and carbon monoxide. Biliverdin is subsequently converted to bilirubin by biliverdin reductase.
In mammals there are three isozymes of heme oxygenase: HO-1 to HO-3. The first two isozymes differ in their tissue expression and their inducibility: HO-1 is highly inducible by its substrate heme and by various non-heme substances, while HO-2 is non-inducible. It has been suggested  that HO-2 could be implicated in the production of carbon monoxide in the brain where it is said to act as a neurotransmitter.
In the genome of the chloroplast of red algae as well as in cyanobacteria, there is a heme oxygenase (gene pbsA) that is the key enzyme in the synthesis of the chromophoric part of the photosynthetic antennae . An heme oxygenase is also present in the bacteria Corynebacterium diphtheriae (gene hmuO), where it is involved in the acquisition of iron from the host heme .
There is, in the central section of these enzymes, a well conserved region centered on a histidine residue. We have used this region as a signature pattern.Last update:
May 2004 / Text revised.
PROSITE method (with tools and information) covered by this documentation:
|Title||Heme oxygenase: function, multiplicity, regulatory mechanisms, and clinical applications.|
|Source||FASEB J. 2:2557-2568(1988).|
|Title||Carbon monoxide: killer to brain messenger in one step.|
|3||Authors||Richaud C., Zabulon G.|
|Title||The heme oxygenase gene (pbsA) in the red alga Rhodella violacea is discontinuous and transcriptionally activated during iron limitation.|
|Source||Proc. Natl. Acad. Sci. U.S.A. 94:11736-11741(1997).|
|Title||Utilization of host iron sources by Corynebacterium diphtheriae: identification of a gene whose product is homologous to eukaryotic heme oxygenases and is required for acquisition of iron from heme and hemoglobin.|
|Source||J. Bacteriol. 179:838-845(1997).|