deficiency. disruption of amino acid metabolism can affect brain development and neurophysiology to affect behavior. for example, fetal protein deficiency decreases the number of neurons in the ca1 region of the hippocampus. glutamate glutamate is a proteinogenic amino acid and neurotransmitter, though it is perhaps publicly best known in its sodium salt form: monosodium glutamate (msg). it is also a flavor on its own, producing the umami or savory flavor found in many fermented foods such as cheese. as an amino acid it acts as a source of fuel for various cellular functions and as a neurotransmitter. glutamate operates as an excitatory neurotransmitter and is released when a nerve impulse excites a glutamate producing cell. this in turn binds to neurons with glutamate receptors, stimulating them. deficiencies and treatments glutamate is a nutrient that is extremely difficult to be deficient in, as, being an amino acid, it is found in every food that contains protein. additionally it is found, as previously mentioned, in fermented foods and in foods containing monosodium glutamate. as such, good sources of glutamate include meat, fish, dairy products and a wide array of other foods. glutamate is also absorbed extremely efficiently by the intestines. however, there are instances of glutamate deficiency occurring, but only in cases where genetic disorders are present. one such example is glutamate formiminotransferase deficiency and can cause either minor or profound physical and intellectual disabilities, depending on the severity of the condition. this disorder is extremely rare however, as only twenty people have so far been identified with this condition. glutamate, while critically important in the body also acts as an excitotoxin in high concentrations not normally found outside of laboratory conditions, although it can occur following brain injury or spinal cord injury. phenylalanine l-phenylalanine is biologically converted into l-tyrosine, another one of the dna-encoded amino acids, and beta-phenethylamine. l-tyrosine in turn is converted into l-dopa, which is further converted into dopamine, norepinephrine (noradrenaline), and epinephrine (adrenaline). the latter three are known as the catecholamines. phenethylamine is further converted into n-methylphenethylamine. phenylalanine uses the same active transport channel as tryptophan to cross the blood–brain barrier, and, in large quantities, interferes with the production of serotonin. phenylketonuria toxic levels of phenylalanine accumulate in the brains of patients with phenylketonuria leading to severe brain damage and intellectual disability. to prevent brain damage, these individuals can restrict dietary phenylalanine intake by avoiding protein and supplementing their diet with essential amino acids.