Cytochrome oxidase (Complex IV) is the rate-limiting enzyme in the electron transport chain responsible for reducing oxygen to water and is linked to oxidative phosphorylation.

“so the more direct measurements would be measurements of oxygen consumption but also could be the enzyme that is responsible for that oxygen consumption and that's where it comes to our work and what we found in the brains of those Alzheimer patients we found that the enzyme called cytochrome oxidase or cytochrome C obviously the complex for in the electron transport chain the electron transfer is the the last trail the last and the rate-limiting enzyme and the one that actually reduces oxygen to water that is linked to oxidative phosphorylation the creation of ATP”