A decapeptide undergoes partial hydrolysis to give peptides whose amino acid composition is shown. Reaction of the intact decapeptide with Edman’s reagent releases PTH-Gly. What is the sequence of the decapeptide?

1.Ala, Trp

2. Val,Pro,Asp

3. Pro, Val

4. Ala, Glu

5. Trp, Ala, Arg

6.Arg, Gly

7.Glu, Ala, Leu

8. Met, Pro, Leu, Glu

The decapeptides are peptides comprised of ten amino acids. The peptides are the amino acid chains interconnected by the peptide bond. The RCONHR’ bond is called the peptide bond. The peptides are composed of two, three, four, five, and ten amino acids known as a dipeptide, tripeptide, tetrapeptide, pentapeptide, and decapeptides.

The N-terminal aminoacid is Gly. Look for a peptide fragment that contains Gly.

Fragment 6 tells that the second amino acid is Arg.

Fragment 5 tells that the next two can be Trp-Ala or Ala-Trp.

Fragment 4 tells that the Glu is next to the Ala. So the third and fourth ones will be Trp-Ala, and the fifth one is Glu.

Fragement 7 tells that the sixth amino acid is Leu.

Fragement 8 tells that the next two are Met-Pro or Pro-Met.

Fragment 3 tells that Pro is next to Val, so the seventh and eighth amino acids must be Met-Pro, and the ninth one is Val.

Finally, fragment 2 tells that the last amino acid is Asp.

Therefore the amino acid sequence is shown below.

Gly-Arg-Trp-Ala-Glu-Leu-Met-Pro-Val-Asp