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.
Tryptophan synthase
Tryptophan synthase is commonly found in Eubacteria, Archaebacteria, Protista, Fungi, and Plantae. It is absent from animals such as humans. Tryptophan is one of the twenty standard amino acids and one of nine essential amino acids for humans. As such, tryptophan is a necessary component of the human diet.