Is mitochondrial reactive oxygen species production proportional to oxygen consumption? A theoretical consideration

It has been assumed that at the whole organismal level, the mitochondrial reactive oxygen species (ROS) production is proportional to the oxygen consumption. Recently, a number of researchers have challenged this assumption, based on the observation that the ROS production per unit oxygen consumed in the resting state of mitochondrial respiration is much higher than that in the active state. Here, we develop a simple model to investigate the validity of the assumption and the challenge of it. The model highlights the significance of the time budget that mitochondria operate in the different respiration states. The model suggests that under three physiologically possible conditions, the difference in ROS production per unit oxygen consumed between the respiration states does not upset the proportionality between the whole animal ROS production and oxygen consumption. The model also shows that mitochondrial uncoupling generally enhances the proportionality. The organismal reactive oxygen species (ROS) production per oxygen consumption (ROS/Oxy) is a constant across animals, if animals allocate their mitochondria to the resting and active states in the same proportion. If one animal allocates more to the resting state than the other animal, then it has a higher ROS/Oxy, and vice versa.