the nonessential amino acids alanine , beta-alanine , arginine , asparagine , aspartic acid , citrulline , cysteine , cystine , glutamic acid , glutamine , d-glutamine , histidine , hydroxyproline , ornithine , proline , serine , tyrosine , and d-tryptophan ;
C0020388
hydroxyproline
C0033382
proline