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Coenzyme Q 10 (CoQ 10 / ˌ k oʊ k j uː ˈ t ɛ n /), also known as ubiquinone, is a naturally occurring biochemical cofactor (coenzyme) and an antioxidant produced by the human body. [ 1 ] [ 2 ] [ 3 ] It can also be obtained from dietary sources, such as meat, fish, seed oils, vegetables, and dietary supplements .
A ubiquinol is an electron-rich (reduced) form of coenzyme Q (ubiquinone). The term most often refers to ubiquinol-10, with a 10-unit tail most commonly found in humans.. The natural ubiquinol form of coenzyme Q is 2,3-dimethoxy-5-methyl-6-poly prenyl-1,4-benzoquinol, where the polyprenylated side-chain is 9-10 units long in mammals.
Ubiquinol (QH 2) binds to the Q o site of complex III via hydrogen bonding to His182 of the Rieske iron-sulfur protein and Glu272 of Cytochrome b. Ubiquinone (Q), in turn, binds the Q i site of complex III. Ubiquinol is divergently oxidized (gives up one electron each) to the Rieske iron-sulfur '(FeS) protein' and to the b L heme.
Cytochrome c diffuses. The first ubiquinol (now oxidised to ubiquinone) is released, whilst the semiquinone remains bound. Round 2: A second ubiquinol is bound by cytochrome b. The 2Fe/2S center and B L heme each pull an electron off the bound ubiquinol, releasing two protons into the intermembrane space.
Resonance structures of a semiquinone. Semiquinones (or ubisemiquinones, if their origin is ubiquinone) are free radicals resulting from the removal of one hydrogen atom with its electron during the process of dehydrogenation of a hydroquinone, such as hydroquinone itself or catechol, to a quinone or alternatively the addition of a single hydrogen atom with its electron to a quinone. [1]
Ubiquinol oxidases (EC 1.10.3.11) are enzymes in the bacterial electron transport chain that oxidise ubiquinol into ubiquinone and reduce oxygen to water. These enzymes are one set of the many alternative terminal oxidases in the branched prokaryotic electron transport chain. [1]