Does ATP production increase with oxygen availability?

Question

I'm not a biologist so pardon any ignorance on my part. I'm working on a speculative evolution project and I'm looking to understand how the partial pressure of oxygen effects the maximum aerobic performance of muscle. This paper gives the maximum aerobic performance of 100 Watts per KG of muscle. This limit is stated to be observed for both insects and vertebrate fliers and is in turn used to calculate the aerobic flight capacities of various animals. The paper also mentions that squamate muscle tissue can achieve 450 W/kg anaerobically.

I have used the equations listed in the linked paper to calculate the size limits of my speculative world's fauna. The only problem is that this assumes an aerobic power output of 100W/kg of muscle. It is my understanding that aerobic respiration in muscle cells is driven by ATP production and that ATP production is dependant on a constant supply of oxygen. It seems logical that the maximum aerobic power output should be higher if there is more oxygen available.

For context, the atmosphere of this speculative world contains 13.5% O2 at a pressure of 12atm. This equates to a partial pressure of oxygen of 1.62 - approximately ~8x higher than our current atmosphere. In these conditions, there is 8 times the amount of oxygen available for respiration. If oxygen availability is the sole factor in ATP production (thus aerobic muscle power), then this means the aerobic power output would net 800W/kg of muscle (assuming the biology of these creatures are the same as known animals). This is almost double what lizards can produce anaerobically which doesn't seem likely.

My question is how would ATP production scale with available oxygen? I assume there comes a point where mitochondria simply cannot process ATP any faster, which would imply a maximum aerobic power output. I have read that some athletes breathe canned air to reduce fatigue. Does more oxygen equate to more power or does it simply mean that muscle cells would not fatigue as quickly? If I've made any mistakes in my reasoning then please correct them. Thanks.

Answer 1

The factors limiting ATP production are the rate of fuel (glucose, fats, amino acids, etc.) metabolism and its efficiency (ATP molecules per fuel molecule).

It is possible to produce ATP with zero oxygen by the glycolytic pathway; if this were not true, there would be no anaerobic organisms on Earth (which there clearly are). Muscle can do this too for short periods of time, producing lactic acid. In fact, many researchers believe that this pathway can produce ATP the fastest of any route of glucose consumption, even though it is least efficient. In other words, the number of ATP per glucose is small (only 2), but glucose "flows" through this pathway so fast that it is still generated faster than by respiration, which produces 30-32 ATP per glucose, but can process far fewer molecules of glucose per second. The actual rate of ATP generation by mitchondria is only limited by O2 concentration, in a chemical kinetics sense, in hypoxia, i.e. when a tissue does not have adequate blood supply, as in certain tumors.

The main effect of oxygen availability is likely size scaling--if you have more O2, you can get it through a larger body more easily. It's not that the muscle cells themselves generate more energy, it's that you can supply more muscle fibers that are farther from the lungs/gills/whatever. That's why in the carboniferous period on Earth, where there was considerably more O2, many animals (particularly invertebrates) were much larger than they are today.