The branched-chain alpha-keto dehydrogenase complex catalyzes the overall conversion of alpha-keto acids to acyl-CoA and CO(2). It contains multiple copies of three enzymatic components: branched-chain alpha-keto acid decarboxylase (E1), lipoamide acyltransferase (E2) and lipoamide dehydrogenase (E3). Within this complex, the catalytic function of this enzyme is to accept, and to transfer to coenzyme A, acyl groups that are generated by the branched-chain alpha-keto acid decarboxylase component. (R)-N(6)-dihydrolipoyl-L-lysyl-[protein] + 2-methylpropanoyl-CoA = (R)-N(6)-(S(8)-2-methylpropanoyldihydrolipoyl)-L-lysyl-[protein] + CoA Binds 1 lipoyl cofactor covalently. Forms a 24-polypeptide structural core with octahedral symmetry. Belongs to the 2-oxoacid dehydrogenase family.