Editing Oxidative phosphorylation (section)

==== Hypoxia/anoxia intolerance ====
Most mammals and birds are intolerant to low/no oxygen conditions. For the heart, in the absence of oxygen, the first four [[Electron transport chain|complexes]] of the electron transport chain decrease in activity.<ref name="Lesnefsky_2017" /> This will lead to protons leaking through the [[inner mitochondrial membrane]] without complexes [[Respiratory complex I|I]], [[Complex III|III]], and [[Complex IV|IV]] pushing protons back through to maintain the proton gradient. There is also electron leak (an event where electrons leak out of the electron transport chain), which happens because [[Nadh dehydrogenase|NADH dehydrogenase]] within Complex I becomes damaged, which allows for the production of ROS ([[reactive oxygen species]]) during ischemia.<ref name="Chen_2007">{{cite journal | vauthors = Chen Q, Camara AK, Stowe DF, Hoppel CL, Lesnefsky EJ | title = Modulation of electron transport protects cardiac mitochondria and decreases myocardial injury during ischemia and reperfusion | journal = American Journal of Physiology. Cell Physiology | volume = 292 | issue = 1 | pages = C137-C147 | date = January 2007 | pmid = 16971498 | doi = 10.1152/ajpcell.00270.2006 }}</ref> This will lead to the reversing of [[ATP synthase|Complex V]], which forces protons from the [[Mitochondrial matrix|matrix]] back into the [[Intermembrane space|inner membrane space]], against their [[Fick's laws of diffusion|concentration gradient]]. Forcing protons against their concentration gradient requires energy, so Complex V uses up ATP as an energy source.<ref name="St-Pierre_2000">{{cite journal | vauthors = St-Pierre J, Brand MD, Boutilier RG | title = Mitochondria as ATP consumers: cellular treason in anoxia | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 97 | issue = 15 | pages = 8670–8674 | date = July 2000 | pmid = 10890886 | pmc = 27006 | doi = 10.1073/pnas.140093597 | doi-access = free | bibcode = 2000PNAS...97.8670S }}</ref>