Oxidative phosphorylation in mitochondria is often monitored by measuring oxygen consumption. When oxidative phosphorylation is proceeding rapidly, the mitochondria will rapidly consume oxygen. If there is little oxidative phosphorylation, only small amounts of oxygen will be used. You are given a suspension of isolated mitochondria and directed to add the following compounds in the order from a to h. With the addition of each compound, all of the previously added compounds remain present. Required:
Predict the effect of each addition on oxygen consumption by the isolated mitochondria.

(a) No effect; mitochondria cannot metabolize glucose.

(b) No effect; no fuel is present to power the synthesis of ATP.

(c) The [O2] falls because citrate is a fuel and ATP can be formed from ADP and Pi.

(d) Oxygen consumption stops because oligomycin inhibits ATP synthesis, which is coupled to the activity of the electron-transport chain.

(e) No effect, for the reasons given in part d.

(f) [O2] falls rapidly because the system is uncoupled and does not require ATP synthesis to lower the proton-motive force.

(g) [O2] falls, though at a lower rate. Rotenone inhibits Complex I, but the presence of succinate will enable electrons to enter at Complex II.

(h) Oxygen consumption ceases because Complex IV is inhibited and the entire chain backs up.

Explanation: