Amino acid composition analysis of an oligopeptide 7 residues long shows that it contains only Asp, Leu, Lys, Met, Phe, Tyr residues. The following facts were observed: 1) Trypsin treatment had no apparent effect.
2) PTH-derivative after one cycle of Edman degradation was phenol-containing amino acid.
3) Brief chymotrypsin treatment yielded several products, including dipeptide and tetrapeptide. The amino acid composition of tetrapeptide was Leu, Lys, Met.
4) Cyanogen bromide treatment yielded a dipeptide, a tetrapeptide and free Lys.
What is the amino acid sequence of this heptapeptde