by omitting single amino acids from the complete synthetic medium , tyrosine , threonine , methionine , isoleucine , phenylalanine , tryptophan , leucine , valine , and cysteine or cystine were found to be essential for stimulation , while lysine , arginine , histidine , hydroxyproline , proline , glutamic acid , aspartic acid , serine , alanine , and glycine were not essential .
C0002520
amino
C0061472
glutamic acid