Converts 2-oxo acids to branched-chain amino acids. Shows activity with L-Leu, L-Ile and L-Val as amino donors and alpha-keto-glutarate as an amino acceptor, but no activity for D-isomers of Leu, Ile, Val, Asp, Glu or Ala. Acts on methionine and its derivatives and the corresponding 2-oxo acids. Catalyzes the initial deamination of methionine to 4-methylthio-2-oxobutyrate as well as the transamination of other typical intermediates of the methionine chain elongation pathway. a 2-oxocarboxylate + L-methionine = 4-methylsulfanyl-2-oxobutanoate + an L-alpha-amino acid Mostly expressed in phloem. Transient induction by wounding. Follows a diurnal rhythm. Reduced methionine-derived aliphatic glucosinolate accumulation, but increased levels of free methionine and S-methylmethionine. Although all the other members of the family possess a branched-chain amino acid aminotransferase activity, the exact function of BCAT4 remains unclear at present. Belongs to the class-IV pyridoxal-phosphate-dependent aminotransferase family.