What would happen if Complex II of the electron transport chain was inhibited?
I understand that ATP can still be produced even if Complex II was inhibited since it is Complexes I,III, IV that directly pump the protons from the matrix into intermembrane space.
I was wondering if anyone could explain the effect on FADH2 when Complex II is inhibited. Thank you very much :)
When Complex II of the electron transport chain is inhibited, it directly affects the flow of electrons and subsequently impacts the production of ATP. Complex II, also known as succinate dehydrogenase, is involved in the transfer of electrons from FADH2 to coenzyme Q (CoQ), which is then passed on to Complex III.
To understand the effect on FADH2 when Complex II is inhibited, let's start with the normal electron transport chain process:
1. In the Krebs cycle, FADH2 is produced as an intermediate step when succinate is converted to fumarate.
2. FADH2 is then oxidized by Complex II, and the electrons are transferred to CoQ.
3. The electrons from CoQ are passed along the electron transport chain through Complexes III and IV, leading to the production of ATP.
Now, if Complex II is inhibited, the flow of electrons from FADH2 to CoQ is halted, and the subsequent transfer of electrons through Complexes III and IV is also affected. This results in several consequences:
1. Decreased ATP production: Since Complex III and Complex IV require an input of electrons from CoQ to efficiently pump protons across the inner mitochondrial membrane, the ATP production rate will be significantly decreased when Complex II is inhibited. However, some ATP can still be produced through Complex I, which receives electrons from NADH.
2. Accumulation of FADH2: With Complex II inhibition, FADH2 will accumulate because it cannot be oxidized by Complex II. The failure to transfer electrons from FADH2 means they cannot contribute to the electron transport chain to produce ATP.
3. Increased succinate levels: Since Complex II is also part of the Krebs cycle, its inhibition can cause an accumulation of succinate. This feedback mechanism occurs because succinate normally serves as a substrate for Complex II; if it cannot be converted to fumarate, there will be an excess of succinate.
In summary, the inhibition of Complex II in the electron transport chain disrupts the normal flow of electrons, leading to decreased ATP production and an accumulation of FADH2 and succinate.