Catalyzes the phosphorylation and inactivation of the branched-chain alpha-ketoacid dehydrogenase complex, the key regulatory enzyme of the valine, leucine and isoleucine catabolic pathways. Key enzyme that regulate the activity state of the BCKD complex. ATP + L-seryl-[3-methyl-2-oxobutanoate dehydrogenase] = ADP + H(+) + O-phospho-L-seryl-[3-methyl-2-oxobutanoate dehydrogenase] Monomer. Ubiquitous. Expression in female liver is influenced by circadian rhythm. Autophosphorylated. Mutant animals are born at the expected Mendelian ratio, but they exhibit a decreased fertility. They are healthy at birth. At 3 weeks of age, they start showing growth retardation. At 12 weeks, they are 15% smaller than their wild-type littermates. Adults develop neurological abnormalities, such as tremors, epileptic seizures and hindlimb clasping. These neurological deficits can be completely abolished when mice are fed with a diet enriched in branched amino acids. Belongs to the PDK/BCKDK protein kinase family.