In the olden days (the 1970s), the sequence of amino acids in a protein was determined by running a series of chemical reactions known as the Edman degradation. This technique worked only on short peptide chains, however, and large proteins had to be broken down into small parts in order to be sequenced. One way to chop large proteins into small chains was with enzymes known as proteases. The protease trypsin breaks the amide bond on the CO₂H side of arginine and lysine, and the protease chymotrypsin breaks the amide bond on the CO₂H side of tyrosine, phenylalanine, and tryptophan. An octapeptide treated with trypsin breaks down to the peptides Ala–Gly–Trp–Gly–Lys and Thr–Val–Lys, and the same octapeptide treated with chymotrypsin breaks down to the peptides Gly–Lys and Thr–Val–Lys–Ala–Gly–Trp. What is the sequence of the octapeptide?