BCKDK or branched chain alpha-keto acid dehydrogenase kinase is an important regulator of the valine, leucine, and isoleucine catabolic pathways. BCKDK is found in the mitochondrion where it phosphorylates and inactivates BCKD. The branched-chain alpha-keto dehydrogenase complex (BCKDH) catalyzes the rate-limiting step in the oxidation of branched-chain amino acids and BCKDK inactivates the BCKDH complex by catalyzing serine phosphorylation of the E1-alpha subunit (1). BCKDH kinase catalyzes the serine phosphorylation of the E1- alpha subunit of BCKDH (2).