CO acts by inhibiting which component of respiratory chain
**Core Concept**
Carbon monoxide (CO) poisoning is a significant occupational hazard and a leading cause of poisoning worldwide. The mechanism of CO toxicity involves the inhibition of cellular respiration, which ultimately leads to tissue hypoxia. In the context of the respiratory chain, CO acts by binding to a specific component, disrupting the normal electron transport process.
**Why the Correct Answer is Right**
CO binds to the iron atom in cytochrome c oxidase (Complex IV), which is a crucial enzyme in the mitochondrial electron transport chain. By binding to the iron atom, CO prevents the enzyme from transferring electrons to oxygen, thereby inhibiting the production of ATP. This results in cellular hypoxia, despite adequate oxygen supply, leading to tissue damage and organ dysfunction.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because CO does not directly inhibit Complex I of the respiratory chain, which is responsible for the transfer of electrons from NADH to ubiquinone.
**Option B:** This option is incorrect as CO does not directly inhibit Complex II of the respiratory chain, which is involved in the transfer of electrons from succinate to ubiquinone.
**Option C:** This option is incorrect because CO does not directly inhibit Complex III of the respiratory chain, which is responsible for the transfer of electrons from ubiquinone to cytochrome c.
**Clinical Pearl / High-Yield Fact**
In CO poisoning, the carboxyhemoglobin (COHb) level is a critical determinant of severity. A COHb level of 20-30% is generally considered to be of moderate severity, while levels above 40% are associated with significant tissue hypoxia and organ dysfunction.
**Correct Answer:** C. Cytochrome c oxidase (Complex IV).