Biochemistry 6th Edition by Reginald Garrett,Charles Grisham

Exercise 4

Solving the sequence of an oligopeptide from sequence analysis data
Analysis of the blood of a catatonic football fan revealed large concentrations of a psychotoxic octapeptide. Amino acid analysis of this octapeptide gave the following results:
The following facts were observed:
a. Partial acid hydrolysis of the octapeptide yielded a dipeptide of the structure

b. Chymotrypsin treatment of the octapeptide yielded two tetrapeptides, each containing an alanine residue.
c. Trypsin treatment of one of the tetrapeptides yielded two dipeptides.
d. Cyanogen bromide treatment of another sample of the same tetrapeptide yielded a tripeptide and free Tyr.
e. End group analysis of the other tetrapeptide gave Asp.
What is the amino acid sequence of this octapeptide?