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lipoic acid:see coenzymecoenzyme
, any one of a group of relatively small organic molecules required for the catalytic function of certain enzymes. A coenzyme may either be attached by covalent bonds to a particular enzyme or exist freely in solution, but in either case it participates intimately in
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6,8-epi-dithio-octanoic acid, a widespread naturally occurring coenzyme, related to enzymes of the class of oxidoreductases. It exists in the form of crystals with melting point 59°-60°C and was first isolated from bull’s liver in 1941 (30 mg of lipoic acid was obtained from 10 tons of liver).
Lipoic acid participates in the transfer of acyl groups (acid radicals) and in biological oxidation reactions (for example, oxidative decarboxylation of pyruvic and ketoglutaric acids for conversion into acetyl-CoA and succinyl-CoA, respectively, with liberation of carbon dioxide). The oxidized form of lipoic acid is transformed into a reduced form, which is then reconverted into the oxidized form upon action of a specific enzyme:
Lipoic acid is the growth factor (vitamin) in certain microorganisms; it exists in composite protein form in the cells of plant and animal tissues.