Lipoic Acid

In pyruvate oxidation by the pyruvate dehydrogenase complex, the acceptor of the aldehyde generated by thiamine pyrophosphate (TPP) is lipoic acid, also called 6,8-dithiooctanoic acid. The carboxyl group of lipoic acid is joined to dihydrolipoamide transacetylase of the complex via an amide bond linking the carboxyl group of lipoic acid to a lysine -amino group of the enzyme. The resulting reactive species is an amide, called lipoamide. Transfer of the active aldehyde moiety from TPP to the sulfur on carbon 6 of lipoamide involves simultaneous oxidation of that moiety, coupled to reduction of the disulfide. This generates an acyl group, which, in pyruvate dehydrogenase, is transferred next to coenzyme A. Thus, lipoamide is both an electron carrier and an acyl group carrier.

See also: Pyruvate Oxidation, Thiamine Pyrophosphate, Dihydrolipoamide Transacetylase, Lipoamide, Coenzyme A

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