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.
PRR23C
Proline is predicted to be the most abundant amino acid in proline-rich protein 23C "Homo sapiens". In comparison to the prevalence of amino acids in other human proteins, it is predicted that proline-rich protein 23C "Homo sapiens" has a higher abundance of proline along with very low abundances of asparagine, threonine, and lysine. Orthologs for this protein are predicted to also have a high abundance of proline.