Problem: The following treatments of a polypeptide yielded the indicated results as amino acids in an acid hydrolysate. What is the primary structure of the polypeptide?
I. Acid hydrolysis 1. (Arg, Asx, 2Cys, Gly, Ile, Leu, Lys, Met, Phe, Pro, Ser)
II. Edman degradation (one cycle) 2. (Leu) 3. (Ser)
III. Carboxypeptidase A (sufficient to remove one residue per chain) 4. (Asp)
IV. 2-mercaptoethanol + iodoacetic acid followed by trypsin hydrolysis. 5. (Arg, Ser) 6. (Asp, Met) 7. (Cys, Gly, Ile, Leu, Phe, Pro) 8. (Cys, Lys)
V. 2-mercaptoethanol + bromoethylamine followed by trypsin hydrolysis:* 9. (Arg, Ser) 10. (Asp, Met) 11. (Cys) 12. (Cys, Gly, Leu) 13. (Ile, Phe, Pro) 14. (Lys)
VI. Chymotrypsin: 15. (no fragments)
VII. Pepsin (pepsin cleaves on the n-terminus of Leu, Phe, Trp, Tyr) 16. (Arg, Asp, 2Cys, Gly, Leu, Lys, Met, Ser) 17. (Ile, Phe, Pro)
* 2-bromoethylamine attaches to Cys and makes a positive amino acid that is cleaved by trypsin