Be sure to answer all parts. An octapeptide contains the following amino acids:

Question

Be sure to answer all parts. An octapeptide contains the following amino acids: Asp, Gln, Ala, His, Arg, Tyr, Leu, Glu Carboxypeptidase treatment of the octapeptide forms His and a heptapeptide. Treatment of the octapeptide with Trypsin forms forms two tetrapeptides, A and B. Treatment of A with Chymotrypsin yields two dipeptides, C and D. Edman degradation cleaves the following amino acids from each peptide: Ala (octapeptide).Ala (A).Glu (B).Ala (C).Leu(D).Partial hydrolysis of tetrapeptide B forms Glu-Gln in addition to other products. Deduce the structure of the octapeptide and fragments A-D. Octapeptide: (select) ??(select) ??(select) ??(select) ? (select) ??(select) ??(select) ?-(select) A: (select) ?-(select) ? (select) ? (select) ? B: | (select) ?-(select) ?-(select) ?-(select) ? C: (select) select) ' D: (select) ? (select) ?

Explanation / Answer

Octapeptide: Ala- Arg- Leu-Tyr- Glu-Gln- Asp- His

A: Ala- Arg- Leu-Tyr

B: Glu-Gln- Asp- His

C: Ala-Arg

D: Leu-Tyr

Carboxy peptidase – Cleaves at the C-terminal

Trypsin - carboxyl side of tyrosine, tryptophan, phenylalanine, leucine, and methionine

Trypsin cleaves at C-terminal end of basic amino acids (arginine and lysine). In general, we write the C-terminal ends on right side of the peptide sequence and the amino acid ends on the left side of the sequence.

Edman degradation – Cleaves from the N-terminal

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