Question

Which of the following is NOT capable to block the action of cytochrome oxidase?

• A. Carbon monoxide
• B. Cyanide
• C. Carbon dioxide
• D. Hydrogen sulphide

Hint:

Complex IV Inhibitors: Cyanide ($ ext{CN}^-$), Carbon Monoxide (CO), Azide ($ ext{N}_3^-$), Hydrogen Sulfide ($ ext{H}_2 ext{S}$). Carbon Dioxide ($ ext{CO}_2$) is NOT an inhibitor.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Cytochrome c oxidase (Complex IV) inhibitors coordinate with the heme $a_3-\text{Cu}_B$ binuclear catalytic center.

Step 2: Detailed Explanation:
Inhibitors of Cytochrome c Oxidase (Complex IV):
1. Cyanide ($\text{CN}^-$): Coordinates strongly to $\text{Fe}^{3+}$ in heme $a_3$, halting electron transfer to $\text{O}_2$.
2. Carbon Monoxide (CO): Competes with $\text{O}_2$ for binding to reduced $\text{Fe}^{2+}$ in heme $a_3$.
3. Hydrogen Sulphide ($\text{H}_2\text{S}$), Azide ($\text{N}_3^-$): Potent inhibitors of the binuclear iron-copper center.
4. Carbon Dioxide ($\text{CO}_2$): A physiological metabolic end product that does not inhibit Complex IV.

Step 3: Final Answer:
Therefore, Carbon dioxide is NOT capable of blocking cytochrome oxidase, matching option (C).