Chapter 27, Problem 59P

An octapeptide contains the following amino acids: Arg, Glu, His, Ile, Leu, Phe, Tyr, and Val. Carboxy peptidase treatment of the octapeptide forms Phe and a heptapeptide. Treatment of the octapeptide with chymotrypsin forms two tetrapeptides, $A$ and $B$. Treatment $A$ of with trypsin yields two dipeptides, $C$ and $D$. Edman degradation cleaves the following amino acids from each peptide: Glu (octapeptide), Glu $\left(A\right)$, Ile $\left(B\right)$, Glu $\left(C\right)$, and Val $\left(D\right)$. Partial hydrolysis of tetrapeptide $B$ forms Ile–Leu in addition to other products. Deduce the structure of the octapeptide and fragments $A-D$.