Figure 2

Enzymatic Synthesis of Carbon Monoxide. Heme is catabolised by heme oxygenases (HO), to form biliverdin, carbon monoxide, and iron. Carbon monoxide can activate soluble guanylyl cyclase, which causes an increase in cyclic guanosine monophosphate levels (cGMP). Biliverdin is subsequently converted to bilirubin by biliverdin reductase.