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. Author manuscript; available in PMC: 2021 Feb 1.
Published in final edited form as: Nitric Oxide. 2019 Dec 20;95:29–44. doi: 10.1016/j.niox.2019.12.002

Figure 4. Pathways of CO synthesis, metabolism, and clearance.

Figure 4.

CO is formed from heme by heme oxygenases 1 and 2 (HO-1, HO-2) in a reaction that requires O2 and produces Fe2+ and biliverdin. Biliverdin is further reduced to bilirubin. CO can bind to various protein-bound heme moieties such as cytochrome oxidase c in tissues and deoxyhemoglobin in blood. CO is carried to the alveoli in the form of carboxyhemoglobin, where it can be exhaled.