Biosynthesis of L-glutamate from L-aspartate or L-cysteine. Important regulator of levels of glutamate, the major excitatory neurotransmitter of the vertebrate central nervous system. Acts as a scavenger of glutamate in brain neuroprotection. The aspartate aminotransferase activity is involved in hepatic glucose synthesis during development and in adipocyte glyceroneogenesis. Using L-cysteine as substrate, regulates levels of mercaptopyruvate, an important source of hydrogen sulfide. Mercaptopyruvate is converted into H(2)S via the action of 3-mercaptopyruvate sulfurtransferase (3MST). Hydrogen sulfide is an important synaptic modulator and neuroprotectant in the brain. 2-oxoglutarate + L-aspartate = L-glutamate + oxaloacetate 2-oxoglutarate + L-cysteine = 2-oxo-3-sulfanylpropanoate + L-glutamate (2S)-2-aminobutanoate + 2-oxoglutarate = 2-oxobutanoate + L-glutamate 2-oxoglutarate + 3-sulfino-L-alanine = 3-sulfinopyruvate + L-glutamate Inhibited by L-aspartate. Optimum pH is 9.7. Homodimer. Expressed in liver and kidney. In liver and kidney, by glucocorticod hormones. Levels in the liver also increase 2-fold on animals fed on a high protein diet or during fasting. By hypoxia during cerebral ischemia. In eukaryotes there are cytoplasmic, mitochondrial and chloroplastic isozymes. Belongs to the class-I pyridoxal-phosphate-dependent aminotransferase family.