CO is released in reaction catalyzed by-
## **Core Concept**
The question tests the understanding of the biochemical pathway involving the release of carbon monoxide (CO). Heme degradation is a critical process where heme, a toxic molecule, is broken down into biliverdin, iron, and carbon monoxide. This process is primarily facilitated by the enzyme heme oxygenase.
## **Why the Correct Answer is Right**
The correct answer, **D. Heme oxygenase**, is the enzyme responsible for catalyzing the degradation of heme into biliverdin, free iron, and carbon monoxide (CO). This reaction is crucial for the recycling of iron and the detoxification of heme. Heme oxygenase exists in different isoforms, including heme oxygenase-1 (HO-1), which is inducible and plays a significant role in protecting against oxidative stress.
## **Why Each Wrong Option is Incorrect**
- **Option A: Cytochrome P450 reductase** - This enzyme is involved in the reduction of cytochrome P450 during the metabolism of various drugs and steroids but is not directly involved in the release of CO from heme.
- **Option B: Biliverdin reductase** - This enzyme catalyzes the conversion of biliverdin to bilirubin, a step further down the heme degradation pathway, but it does not release CO.
- **Option C: Ferrochelatase** - This enzyme is involved in the biosynthesis of heme, catalyzing the insertion of ferrous iron into protoporphyrin IX, the opposite of heme degradation.
## **Clinical Pearl / High-Yield Fact**
A key clinical point to remember is that carbon monoxide, although toxic in high concentrations, has signaling properties at low concentrations, similar to nitric oxide. Heme oxygenase and the products of heme degradation, including CO, biliverdin (and its conversion to bilirubin), and free iron, have antioxidant and anti-inflammatory effects.
## **Correct Answer: D. Heme oxygenase**