BCAT1 and glioblastoma: Glioblastoma cells also synthesize large amounts of the excitatory neurotransmitter glutamate from α-ketoglutarate via branched chain amino acid transaminase-1 (BCAT-1) [17] which is released into the tumor microenvironment at high concentrations via the glutamate-cystine antiporter system xc [18, 19].