Organic Chemistry

998 CHAPTER 23 Amino Acids, Peptides, and Proteins

56. Determine the amino acid sequence of a polypeptide from the following results:
    a. Complete hydrolysis of the peptide yields the following amino acids: Ala, Arg, Gly, 2 Lys, Met, Phe, Pro, 2 Ser, Tyr, Val.
    b. Treatment with Edman’s reagent gives PTH-Val.
    c. Carboxypeptidase A releases Ala.
    d. Treatment with cyanogen bromide yields the following two peptides:
    
    
    1. Ala, 2 Lys, Phe, Pro, Ser, Tyr
    
    
    2. Arg, Gly, Met, Ser, Val
       e. Treatment with chymotrypsin yields the following three peptides:
    
    
    3. 2 Lys, Phe, Pro
    
    
    4. Arg, Gly, Met, Ser, Tyr, Val
    
    
    5. Ala, Ser
       f. Treatment with trypsin yields the following three peptides:
    
    
    6. Gly, Lys, Met, Tyr
    
    
    7. Ala, Lys, Phe, Pro, Ser
    
    
    8. Arg, Ser, Val
    
    
    
    


57. The C-terminal end of a protein extends into the aqueous environment surrounding the protein. The C-terminal amino acids are
    Gln, Asp, 2 Ser, and three nonpolar amino acids. Assuming that the for formation of a hydrogen bond is and the
    for removal of a hydrophobic group from water is calculate the for folding the C-terminal end of the
    protein into the interior of the protein under the following conditions:
    a. All the polar groups form one intramolecular hydrogen bond.
    b. All but two of the polar groups form intramolecular hydrogen bonds.


58. Professor Mary Gold wanted to test her hypothesis that the disulfide bridges that form in many proteins do so after the minimum
    energy conformation of the protein has been achieved. She treated a sample of lysozyme, an enzyme containing four disulfide
    bridges, with 2-mercaptoethanol and then added urea to denature the enzyme. She slowly removed these reagents so that the
    enzyme could refold and reform the disulfide bridges. The lysozyme she recovered had 80% of its original activity. What would be
    the percent activity in the recovered enzyme if disulfide bridge formation were entirely random rather than determined by the
    tertiary structure? Does this experiment support Professor Gold’s hypothesis?

¢G° - 4 kcal>mol, ¢G°

¢G° - 3 kcal>mol

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