Amino acid analysis (AAA) is performed by liquid-phase hydrolysis of the peptide with constant-boiling hydrochloric acid (6N HCl) followed by pre-column derivatization of the free amino acids. The derivatized amino acids are separated by RP-HPLC. Integration of the individual peaks allows the determination of the amino acid composition of the peptide hydrolysate. However, the indole moiety of Trp is destroyed during hydrolysis; the side-chain amide groups of Asn and Gln and the lactam cycle of Pyr, will be hydrolyzed yielding Asp and Glu, respectively. Hence, these amino acids are listed as Asx and Glx in the AAA result.