Catalyzes the first reaction in the catabolism of the essential branched chain amino acids leucine, isoleucine, and valine. 2-oxoglutarate + L-leucine = 4-methyl-2-oxopentanoate + L-glutamate 2-oxoglutarate + L-isoleucine = (S)-3-methyl-2-oxopentanoate + L-glutamate 2-oxoglutarate + L-valine = 3-methyl-2-oxobutanoate + L-glutamate Homodimer. During embryogenesis, expressed in the brain and kidney. Overexpressed in MYC-induced tumors such as Burkitt's lymphoma. Belongs to the class-IV pyridoxal-phosphate-dependent aminotransferase family.