FCH 530 Homework 2
1. Treatment of a polypeptide by dithiothreitol yields two polypeptides that have the
following amino acids:
1. Ala-Phe-Cys-Met-Tyr-Cys-Leu-Trp-Cys-Asn
2. Val-Cys-Trp-Val-Ile-Phe-Gly-Cys-Lys
Chymotrypsin-catalyzed hydrolysis of the intact polypeptide yields polypeptide
fragments with the following amino acid compositions:
3.
4.
5.
6.
7.
Ala, Phe
Asn, Cys2, Met, Tyr
Cys, Gly, Lys
Cys2, Leu, Trp2, Val
Ile, Phe, Val
Indicate the positions of the disulfide bonds in the original polypeptide.
2. The following treatments of a polypeptide yielded the indicated results. What is the
primary structure of the polypeptide?
I. Acid hydrolysis:
1. (Arg2, Cys2, Gln, Ile, Leu, Lys, Met, Phe, Trp)
II. Edman degradation (one cycle)
2. (Met)
3. (Phe)
III. Carboxypeptidase A (sufficient time to remove one residue per chain):
4. (Ser)
V. Trypsin
5. (Lys, Met)
6. (Arg , Cys2, Trp, Gln, Ser, Ile)
7. (Arg, Leu, Phe)
VI. Chymotrypsin
7. (Arg2, Cys2,Ile, Leu, Lys, Met, Trp)
8. (Phe)
9. (Ser, Gln)
VII. Dithiothreitiol + iodoacetic acid followed by trypsin hydrolysis
10. (Lys, Met)
11. (Cys, Gln, Ser, Trp)
12. (Arg, Leu, Phe)
13 (Arg, Cys, Ile)
VIII. Dithiothreitol + 2-bromoethylamine followed by trypsin hydrolysis
13. (Lys, Met)
14. (Cys)
15. (Gln, Ser, Trp)
16. (Arg, Leu, Phe)
17. (Cys)
18. (Arg, Ile)
X. Dithiothreitiol + iodoacetic acid followed by chymotrypsin
23. (Cys, Lys, Met, Trp)
24. (Gln, Ser)
25. (Phe)
26. (Arg2, Cys, Ile, Leu)
XI.
28.
29.
30.
Pepsin
(Phe)
(Arg2 ,Met, Lys, Cys2 , Ile, Leu)
(Gln, Ser, Trp)
XII. Dithiothreitiol + iodoacetic acid followed by pepsin
32. (Cys, Met, Lys)
33. (Gln, Ser, Trp)
34. (Arg2, Cys, Ile, Leu)
35. (Phe)
What is the primary structure of the polypeptide?
Draw out the structure of the original polypeptide at pH 7.0. (show all amino acids and
side chains)
What are the pKs of the ionizable groups?
What is the pI of this polypeptide?
3. Define primary structure, secondary structure, tertiary structure, and quaternary
structure and give an example as it applies to biochemistry.
4. Give an example how CNBr would be important for protein sequencing.
5. Write out an example of an -amino group protection and an -carboxyl group
protection.
Draw the Newman projections for the following diastereomers of Thr. What are the RS
configurations for each stereoisomer?