Oxygen serves as the final electron acceptor in the mitochondrial electron transport chain and as this, it is a key factor in regulation of energy expenditure.
By controlling oxygen intake, levels of ADP-ribose on the ATP synthase can be manipulated and mitochondria ATP production regulated accordingly. When oxygen levels are low (e.g., during strenuous exercise), NAD+ concentrations fall below ADP-ribose concentrations and there is competition for ADP-ribose among three enzymes: Complex I, complex II, and complex III [complex III has higher affinity for ADP-ribose than does complex II]. If the activity of these enzymes is relatively equal, little or no ATP will be produced because these complexes do
