Converts 2-oxo acids to branched-chain amino acids. Acts on leucine, isoleucine and valine. Also involved in methionine chain elongation cycle of aliphatic glucosinolate formation. Catalyzes the conversion of 5-methylthiopentyl-2-oxo and 6-methylthiohexyl-2-oxo acids to their respective Met derivatives, homomethionine and dihomo-methionine, respectively. 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 a 2-oxocarboxylate + L-methionine = 4-methylsulfanyl-2-oxobutanoate + an L-alpha-amino acid Inhibited by Ser- or Thr-derived imine. Amino-acid biosynthesis; L-isoleucine biosynthesis; L-isoleucine from 2-oxobutanoate: step 4/4. Amino-acid biosynthesis; L-leucine biosynthesis; L-leucine from 3-methyl-2-oxobutanoate: step 4/4. Amino-acid biosynthesis; L-valine biosynthesis; L-valine from pyruvate: step 4/4. A number of isoforms are produced. According to EST sequences. Expressed in the phloem cells. Diurnally expressed. No effect on the levels of free amino acids in seeds, but reduced levels of Val, Ser and Thr in leaves. Increased levels of Met-derived glucosinolates in leaves. Branched-chain amino acids are synthesized in chloroplasts, whereas the degradation takes place in mitochondria. Belongs to the class-IV pyridoxal-phosphate-dependent aminotransferase family.