Glutamine
Glutamine is the most abundant naturally occurring, nonessential amino acid in the human body, and one of the few amino acids that can directly cross the blood–brain barrier. Humans obtain glutamine through catabolism of proteins in foods they eat. In states where tissue is being built or repaired, like growth of babies, or healing from wounds or severe illness, glutamine becomes conditionally essential.
Serine
-serine was thought to exist only in bacteria until relatively recently; it was the second amino acid discovered to naturally exist in humans, present as a signaling molecule in the brain, soon after the discovery of -aspartate. Had amino acids been discovered in humans sooner, the glycine site on the NMDA receptor might instead be named the -serine site. Apart from central nervous system, -serine plays a signaling role in peripheral tissues and organs such as cartilage, kidney and corpus cavernosum.