1WNW

Heme oxygenase (HO) catalyses the breakdown of heme to release biliverdin, CO, and free iron, and is found in mammals, plants and photosynthetic bacteria. The roles of the heme catabolism process are different in mammals and plants: whilst mammals use HO to degrade excess heme from red blood cells, plants and cyanobacteria use HO activity in order to generate the biliverdin needed for the production of light harvesting complexes. As a result, their is little sequence or structural homology between the mammalian and other forms, indicating that they may have evolved independently. However, the reaction seems to proceed via the same mechanism in both, with key active site residues being the same between the two groups. The bacterial form is described here, but the catalytic residues are the same in both the mammalian and plant forms of the enzyme.