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The oxygen reduction reaction is an essential reaction for aerobic organisms. Such organisms are powered by the heat of combustion of fuel (food) by O 2.Rather than combustion, organisms rely on elaborate sequences of electron-transfer reactions, often coupled to proton transfer.
In the electron transport chain, electrons are passed through a series of proteins via oxidation-reduction reactions, with each acceptor protein along the chain having a greater reduction potential than the previous. The last destination for an electron along this chain is an oxygen molecule.
Although cellular respiration is technically a combustion reaction, it is an unusual one because of the slow, controlled release of energy from the series of reactions. Nutrients that are commonly used by animal and plant cells in respiration include sugar , amino acids and fatty acids , and the most common oxidizing agent is molecular oxygen ...
For example, an enzyme that catalyzed this reaction would be an oxidoreductase: A – + B → A + B – In this example, A is the reductant (electron donor) and B is the oxidant (electron acceptor). In biochemical reactions, the redox reactions are sometimes more difficult to see, such as this reaction from glycolysis:
In reactions involving donation of a hydrogen atom, oxygen is reduced to water (H 2 O) or hydrogen peroxide (H 2 O 2). Some oxidation reactions, such as those involving monoamine oxidase or xanthine oxidase, typically do not involve free molecular oxygen. [1] [2] The oxidases are a subclass of the oxidoreductases. The use of dioxygen is the ...
Dioxygenases, or oxygen transferases, incorporate both atoms of molecular oxygen (O 2) into the product(s) of the reaction. [ 3 ] Among the most common monooxygenases are the cytochrome P450 oxidases , responsible for breaking down numerous chemicals in the body.
After being carried in blood to a body tissue in need of oxygen, O 2 is handed off from the heme group to monooxygenase, an enzyme that also has an active site with an atom of iron. [9] Monooxygenase uses oxygen for many oxidation reactions in the body. Oxygen that is suspended in the blood plasma equalizes into the tissue according to Henry's law.
The oxygen is rapidly reduced, with two electrons coming from the Fe 2+-cytochrome a 3, which is converted to the ferryl oxo form (Fe 4+ =O). The oxygen atom close to Cu B picks up one electron from Cu +, and a second electron and a proton from the hydroxyl of Tyr(244), which becomes a tyrosyl radical. The second oxygen is converted to a ...