branched-chain α-keto acid dehydrogenase

branched-chain α-ke·to ac·id de·hy·dro·gen·ase (brancht chān keґto asґid de-hiґdro-jən-ās) an enzyme of the oxidoreductase class that is a component of the multienzyme branched-chain α-keto acid dehydrogenase complex (q.v.). The enzyme catalyzes the oxidative decarboxylation of the branched chain amino acids leucine, isoleucine, and valine, transferring the products formed to the lipoamide that is linked to the side chain of a lysine residue of another enzyme of the complex, dihydrolipoyllysine-residue (2-methylpropanoyl)transferase, using a thiamine pyrophosphate cofactor. See also maple syrup urine disease, under disease. Called also α-ketoisovalerate dehydrogenase. In official nomenclature, called 3-methyl-2-oxobutanoate dehydrogenase (2-methylpropanoyl-transferring) [EC 1.2.4.4].