Question

Reaction of a polypeptide with carboxypeptidase A releases Met. The polypeptide undergoes partial hydrolysis to give the following peptides.

What is the sequence of the polypeptide?

1. Ser, Lys, Trp4. Leu, Glu, Ser 7. Glu, His 10. Glu, His, Val

2. Gly, His, Ala 5. Met, Ala, Gly8. Leu, Lys, Trp11. Trp, Leu, Glu

3. Glu, Val, Ser 6. Ser, Lys, Val 9. Lys, Ser 12. Ala, Met

Short answer

The sequence of the given polypeptide is Ser-Glu-Leu-Trp-Lys-Ser-Val-Glu-His-Gly-Ala-Met.

Step-by-step solution

Polypeptide

Polypeptides constitute a continuous peptide chain that does not have branches. Protein is a term used to denote a polypeptide comprising greater than fifty amino acids.

Identifying the sequence of the polypeptide

The reaction of the polypeptide with carboxypeptidase A releases Met.

Hence, the C-terminal amino acid of the given polypeptide is Met.

Fragment 12 tells us the amino acid near Met is Ala.

Fragment 5 tells us the next amino acid is Gly.

Fragment 2 tells the next amino acid is His.

Fragment 7 tells the next amino acid is Glu.

Fragment 10 tells the next amino acid is Val.

Fragment 3 tells the next amino acid is Ser.

Fragment 9 tells the next amino acid is Lys.

Fragment 1 tells the next amino acid is Trp.

Fragment 8 tells the next amino acid is Leu.

Fragment 11 tells the next amino acid is Glu.

Fragment 4 tells the next (first ) amino acid is Ser.

Hence, the sequence of the given polypeptide is Ser-Glu-Leu-Trp-Lys-Ser-Val-Glu-His-Gly-Ala-Met.