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?