Question

Which among the following is an inhibitor of complex I of ETC?

• A. Carboxin
• B. Carbon monoxide
• C. Rotenone
• D. Antimycin A

Answer 1

The correct option is C Rotenone

Electron transport chain (ETC) is in the inner mitochondrial membrane and it has four complexes that accept and carry electrons released from $NADH+H^{+}$ and $FAD{H}_2$. As the electrons move through different complexes, they release energy. This energy is utilized to pump protons from the matrix to the intermembrane space. This increases the concentration of protons in the intermembrane space and creates a driving force. Later protons move through complex V (ATP synthase) into the matrix and there is synthesis of ATP.

Rotenone is an inhibitor of complex I of the ETC (Electron transport chain). Complex I is also known as NADH dehydrogenase complex. It has FMN (flavin mononucleotide) and iron-sulfur centres. $NADH+H^{+}$ generated during glycolysis and the Krebs cycle gets oxidised in complex I and electrons released from $NADH+H^{+}$ are accepted by FMN of complex I.
From FMN, electrons are transferred to Fe-S (iron- sulfur) centre of complex I. From Fe-S, electrons are transferred to ubiquinone, a mobile carrier of electrons. Rotenone inhibits the flow of electrons from Fe-S (iron-sulfur protein) to ubiquinone.

Carboxin is an inhibitor of complex II of ETC.

Carbon monoxide is an inhibitor of complex IV of ETC.

Antimycin A is an inhibitor of complex III of ETC.