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heme oxygenase Heme oxygenase (HO, EC 1.14.14.18) catalyzes the rate limiting step in the degradation of heme to biliverdin in a multi-step reaction. HO is essential for recycling iron from heme which is used as a substrate and cofactor for its own degradation to biliverdin, iron, and carbon monoxide. This family serves a variety of specific needs in different branches of life: in vertebrates, HO plays a role in heme homeostasis and oxidative stress response, and cellular signaling in mammals that include isoforms HO-1 and HO-2; in photosynthetic organisms including cyanobacteria, algae, and higher plants, biliverdin is used for photosynthetic pigment formation or light-sensing; and, in pathogenic bacteria, HO is part of a pathway for iron acquisition from host heme and heme products. HO shares tertiary structure similarity to methane monooxygenase (EC 1.14.13.25), ribonucleotide reductase (EC 1.17.4.1) and thiaminase II (EC 3.5.99.2), but shares little sequence homology.
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Jiyao W et al.(2023). "The conserved domain database in 2023.",