There is but a single enzyme-catalyzed reaction in the human body known to generate carbon monoxide (CO) as one of its products. Which of the following enzymes represents the one that catalyzes this CO-producing reaction?

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Quizplus · Accepted Answer

Heme oxygenase is the enzyme responsible for the degradation of heme, resulting in the production of biliverdin, free iron, and carbon monoxide (CO) as byproducts. Heme is oxidized, with the heme ring being opened by the endoplasmic reticulum enzyme, heme oxygenase (see Figure 33-5). The oxidation step requires heme as a substrate, and any hemin (Fe³⁺) is reduced to heme (Fe²⁺) prior to oxidation by heme oxygenase. The oxidation occurs on a specific carbon producing the linear tetrapyrrole biliverdin, ferric iron (Fe³⁺), and CO. This is the only reaction in the body that is known to produce CO. Most of the CO is excreted through the lungs, with the result that the CO content of expired air is a direct measure of the activity of heme oxidase in an individual.

There Is but a Single Enzyme-Catalyzed Reaction in the Human