The single branched-chain α-ketoacid dehydrogenase complex (BCKDC) in mitochondria catalyzes the irreversible oxidative decarboxylation of branch-chain α-ketoacids (BCKA), the second common step in the degradation of branched-chain amino acids (BCAA) leucine, isoleucine, and valine. The homeostasis of BCAA is critical in health and disease, participating in the reduction oxidative stress, which in turn promotes survival in rats with advanced liver cirrhosis and supports mitochondrial biogenesis in cardiac and skeletal muscle. In patients with inherited maple syrup urine disease (MSUD), the accumulation of BCAA and BCKA caused by the dysfunction of BCKDC leads to sometimes fatal acidosis, neurological derangement, and mental retardation. Additionally, high blood BCAA concentrations are linked to the development of insulin resistance and are useful metabolic markers in type 2 diabetes risk assessment[1]. Branched-chain alpha-keto acid dehydrogenase kinase (BDK; EC 2.7.11.4) is one of the regulating enzymes of BCKDC (BDP; 3.1.3.16 is the other enzyme), and phosphorylates and inactivates the BCKDC. The inactivation of BCKDC through phosphorylation by BDK results in increased BCAA concentrations in animal tissues. Therefore, modulation of BDK activity constitutes a major mechanism for BCAA homeostasis in vivo[2].