30. Peptides and Proteins

Bradykinin is an important nonapeptide with many biological functions. A student performed a series of experiments to determine its structure and obtained the following results:

1. Complete hydrolysis of the peptide yielded 2 Arg, 2 Phe, 3 Pro, Gly, and Ser.

2. Edman degradation produced PTH-Arg.

3. Treatment with carboxypeptidase A did not produce any fragments.

4. Treatment with chymotrypsin produced Arg, a pentapeptide, and a tripeptide with composition Pro, Ser, Phe.

5. A tripeptide produced during partial acidic hydrolysis was confirmed to be Pro-Gly-Phe.

Use the following information to determine the structure of a synthetic heptapeptide:

1. Complete hydrolysis of the peptide yields 2 Thr, Cys, Met, Trp, Lys, and Phe.

2. Edman degradation produces PTH-Phe.

3. Treatment with carboxypeptidase A cleaves off Thr.

4. Cleavage with cyanogen bromide produces a dipeptide and a pentapeptide

5. Treatment with trypsin produces a tetrapeptide and a tripeptide Thr-Cys-Thr.