Glutamine
In human blood, glutamine is the most abundant free amino acid.
Taste
The savory taste (known in Japanese as "umami") was identified by Japanese chemist Kikunae Ikeda of Tokyo Imperial University, which signals the presence of the amino acid L-glutamate, triggers a pleasurable response and thus encourages the intake of peptides and proteins. The amino acids in proteins are used in the body to build muscles and organs, transport molecules (hemoglobin), antibodies, and the organic catalysts known as enzymes. These are all critical molecules, and as such it is important to have a steady supply of amino acids, hence the pleasurable response to their presence in the mouth.