This enzyme system catalyses the oxidative decarboxylation of branched-chain alpha-keto acids derived from L-leucine, L-isoleucine, and L-valine to branched-chain acyl-CoAs. It belongs to the 2-oxoacid dehydrogenase system family, which also includes EC 22.214.171.124, pyruvate dehydrogenase system, EC 126.96.36.199, 2-oxoglutarate dehydrogenase system, EC 188.8.131.52, glycine cleavage system, and EC 184.108.40.206, acetoin dehydrogenase system. With the exception of the glycine cleavage system, which contains 4 components, the 2-oxoacid dehydrogenase systems share a common structure, consisting of three main components, namely a 2-oxoacid dehydrogenase (E1), a dihydrolipoamide acyltransferase (E2), and dihydrolipoamide dehydrogenase (E3). The reaction catalysed by this system is the sum of three activities: EC 220.127.116.11, 3-methyl-2-oxobutanoate dehydrogenase (2-methylpropanoyl-transferring), EC 18.104.22.168, dihydrolipoyllysine-residue (2-methylpropanoyl)transferase, and EC 22.214.171.124, dihydrolipoyl dehydrogenase. The system also acts on (S)-3-methyl-2-oxopentanoate and 4-methyl-2-oxopentanoate.
EC 126.96.36.199 created 1972, modified 2019, modified 2020