Somatostatin is a tetradecapeptide of the hypothalamus that inhibits the release of pituitary
growth hormone. Its amino acid sequence has been determined by a combination of Edman
degradations and enzymic hydrolysis experiments. On the basis of the following data, deduce the
primary structure of somatostatin: 1. Eduman degradation gave PTH-Ala. 2. Selective hydrolysis
gave peptides having the following sequences: Phe-Trp Thr-Ser-Cys Lys-Thr-Phe Thr-Phe-Thr-
Ser-Cys Asn-Phe-Phe-Trp-Lys Ala-Gly-Cys-Lys-Asn-Phe 3. Somatostatin has a disulfide bridge
N- -C
Solution
Edmann's method always separates the N- terminal amino acid. Since Edmann method gives
PTH- alanine, the N- terminal amino acid is Alanine.
SO, the part of sequence is:
Ala- gly-Cys-Lys-Asn-Phe.
The complete sequence is:
Ala- Gly-Cys-Lys-Asn-Phe- Phe- Trp-Lys-Thr-Phe-Thr-Ser-Cys
the disulfide linkage is in between Cys (3rd amino acid from N-terminal) and Cys (C- terminal
amino acid)