Oxidative phosphorylation is regulated by the energy needs of cells, primarily the levels of ADP compared to ATP, following Le Chatelier’s Principle of chemical equilibria.
Consider a reaction that goes in both ways. What would happen if the reactants buildup? Obviously, the reaction will be driven forward to spend those reactants and form more products. If the products start to increase more than their equilibrium concentration, in that case the reaction will go reverse towards the reactants. That is what Le Chatelier says.
Now, let’s apply that principle to oxidative phosphorylation which is responsible for much of the ATP generated in cells. What would happen if more reactants, namely the electron carriers NADH and FADH2, ADP, and free phosphate, were present in a cell? Yes, that would drive oxidative phosphorylation forward, leading to higher ATP production. Of these reactants, ADP is the most limiting factor, as cells are capable of maintaining stable ratios of NAD+ and NADH. Thus, the ADP levels in a cell are most likely to alert the electron transport chain to produce more ATP. Alternatively, elevated levels of ATP in a cell or elevated levels of the oxidized forms of the electron carrier molecules would shift oxidative phosphorylation in the opposite direction. That means the flow of electrons through the electron transport chain would be slower and less ATP would be produced.
MCAT Official Prep (AAMC)
• Oxidative phosphorylation is regulated primarily by the energy needs of a cell, and therefore the ratio of ADP to ATP.
Oxidative phosphorylation: The final stage of cellular respiration where the combined action of the electron transport chain and chemiosmotic coupling result in ATP production.
Le Chatelier’s Principle: States that changes in the concentration of reactants (as well as temperature, volume, or pressure) will affect the chemical equilibrium of a chemical reaction.