The electron flow in Cytochrome C oxidase can be blocked by:
**Core Concept**
Cytochrome C oxidase is a crucial enzyme in the mitochondrial electron transport chain, responsible for transferring electrons from cytochrome C to molecular oxygen, generating a proton gradient for ATP synthesis.
**Why the Correct Answer is Right**
The electron flow in Cytochrome C oxidase is blocked by Cyanide (CN-), a potent inhibitor that binds to the iron atom in the heme a3 subunit, preventing the transfer of electrons to oxygen. This results in the accumulation of reducing equivalents, leading to the inhibition of the electron transport chain and ultimately, the cessation of ATP synthesis. The high affinity of cyanide for the heme a3 subunit makes it a highly effective inhibitor of Cytochrome C oxidase.
**Why Each Wrong Option is Incorrect**
**Option A:** Rotenone is a inhibitor of Complex I (NADH dehydrogenase) of the electron transport chain, not Cytochrome C oxidase.
**Option B:** Antimycin A is an inhibitor of Complex III (cytochrome b-c1 complex) of the electron transport chain, not Cytochrome C oxidase.
**Option C:** Atractyloside is an inhibitor of the ADP/ATP translocase, not an inhibitor of the electron transport chain.
**Clinical Pearl / High-Yield Fact**
Cyanide poisoning is a medical emergency that requires prompt treatment with hydroxocobalamin or other antidotes to reverse the inhibition of Cytochrome C oxidase and restore ATP synthesis.
**Correct Answer:** C. Cyanide