Treatment of a polypeptide by dithiothreitol yields two polypeptides that have t

Question

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. Ala, Phe

4. Asn, Cys 2 , Met, Tyr

5. Cys, Gly, Lys

6. Cys 2 , Leu, Trp2, Val

7. Ile, Phe, Va

Can someone please explain how you know where the disulfide bonds go? I already have the answer for this but I just don't understand how to get it. Thank you (:

Also, what does Cys 2 mean?

Explanation / Answer

the disulphide bonds in the amino acids have bond dissociation energy of 60/Kcal /mole which is comparitively lower then carbon bonds. disulphide bonds are ussualy considered a weak link in biomolecules. polarizability of sulphur s-s is susseptible to attack from neucleophiles as well as electrophiles.

clevage occurs from reduction, compounds like sodium bicarbonate carry out the process of scisson.Metal thiolate are formed due to this reaction. the thiolate group S(-) attacks the sulphur of disulphide bond and the bond gets broken.

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