Glutamic acid (abbreviated as Glu or E). It is not among the human essential amino acids.

Glutamic acid is the single largest contributor to intestinal energy. As a source for umami, ninety-five percent of dietary glutamate is metabolized by intestinal cells in a first pass.  All meats, poultry, fish, eggs, as well as dairy products are excellent sources of glutamic acid. Some protein-rich plant foods also serve as sources.

Glutamate is a key molecule in cellular metabolism. In humans, dietary proteins are broken down by digestion into amino acids, which serves as metabolic fuel for other functional roles in the body.

Glutamate is the most abundant swift excitatory neurotransmitter in the mammalian nervous system. At chemical synapses, glutamate is stored in vesicles. Nerve impulses trigger release of glutamate from the pre-synaptic cell. In the opposing post-synaptic cell, glutamate receptors, such as the NMDA receptor, bind glutamate and are activated. Because of its role in synaptic plasticity, it is believed that glutamic acid is involved in cognitive functions like learning and memory in the brain.

References

Okumoto, S., et al. (2005). "Detection of glutamate release from neurons by genetically encoded surface-displayed FRET nanosensors". Proceedings of the National Academy of Sciences U.S.A 102 (24): 8740-8745. PMID 15939876.? Free text