analysis of two of these showed that both had similar amino acid compositions with 26 % half-cystine , 16 % glycine , and very low levels of the aromatic amino acids phenylalanine and tyrosine ( 0.3-0.5 % ) , histidine ( 0.4 % ) , methionine ( about 0.5 % ) , and leucine ( about 1 % ) .
C0002520
amino acid
C0017890
glycine