Question

Use the given experimental data to deduce the sequence of an octapeptide that contains the following amino acids: Ala, Gly (2 equiv), His (2 equiv), Ile, Leu and Phe. Edman degradation cleaves Gly from the octapeptide, and carboxypeptidase forms Leu and a heptapeptide. Partial hydrolysis forms the following fragments: Ile-His-Leu, Gly, Gly-Ala-Phe-His, and Phe-His-Ile.

Short answer

The sequence of an octapeptide is Gly-Gly-Ala-Phe-His-Ile-His-Leu.

Step-by-step solution

Octapeptide

An octapeptide is a continuous polypeptide chain and contains eight amino acids.It cleaves into smaller fragments when octapeptide is treated with chymotrypsin, trypsin, and carboxypeptidase.

Sequence of an octapeptide.

The given fragments are Ile-His-Leu, Gly, Gly-Ala-Phe-His, and Phe-His-Ile.

Here, Phe-His-Ile has Phe-His common to Gly-Ala-Phe-His and Ile is common to Ile-His-Leu. These three fragments are joined together by taking common amino acids as one.

The sequence of octapeptide obtained is Gly-Gly-Ala-Phe-His-Ile-His-Leu. Gly comes at the front of the sequence as it is cleaved by Edman degradation, and Leu comes at last because carboxypeptidase forms Leu and heptapeptide.

The sequence of an octapeptide