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 calcium ions. Homodimer. Expressed in neurons of the retina. Localizes to the inner and outer plexiform layers, the inner and outer nuclear layer and the outer segments of photoreceptors. In eukaryotes there are cytoplasmic, mitochondrial and chloroplastic isozymes. Belongs to the class-I pyridoxal-phosphate-dependent aminotransferase family.