Glutamate (neurotransmitter)
Glutamate is a major constituent of a wide variety of proteins; consequently it is one of the most abundant amino acids in the human body. Under ordinary conditions enough is obtained from the diet that there is no need for any to be synthesized. Nevertheless, glutamate is formally classified as a non-essential amino acid, because it can be synthesized from alpha-Ketoglutaric acid, which is produced as part of the citric acid cycle by a series of reactions whose starting point is citrate. Glutamate cannot cross the blood-brain barrier unassisted, but it is actively transported into the nervous system by a high affinity transport system, which maintains its concentration in brain fluids at a fairly constant level.
Boletus edulis
A comparative study of the amino acid composition of eleven Portuguese wild edible mushroom species showed "Boletus edulis" to have the highest total amino acid content, about 2.3 g per 100 g of dried mushroom. This total includes a full complement of 20 essential and nonessential amino acids. Analysis of the free amino acids (that is, those not bound up in protein) revealed glutamine and alanine to be the principal amino acids (each about 25% of total compounds); a separate analysis concluded that lysine is another predominant compound.