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) (By similarity). Required during sugar starvation and acts under the control of a sugar-sensing mechanism involving Ser/Thr kinases and phosphatases. (R)-N(6)-lipoyl-L-lysyl-[dihydrolipoyllysine-residue (2-methylpropanoyl)transferase] + 3-methyl-2-oxobutanoate + H(+) = (R)-N(6)-(S(8)-2-methylpropanoyldihydrolipoyl)-L-lysyl-[dihydrolipoyllysine-residue (2-methylpropanoyl)transferase] + CO2 Heterotetramer of alpha and beta chains. Expressed in the non-photosynthetic organs such as siliques, flowers and roots. Barely detected in non senescent green leaves, accumulated slightly at the early stage of leaf senescence and strongly expressed at the late stage of leaf senescence. By dark treatment. Down-regulated by sucrose in a hexokinase dependent manner. Up-regulated by Leucine and its derivative alpha-keto acid (KIC).