29. Amino Acids

What alkyl halide is used in the acetamidomalonic ester synthesis to prepare

b. phenylalanine?

What alkyl halide is used in the acetamidomalonic ester synthesis to prepare

a. lysine?

Reaction of a polypeptide with carboxypeptidase A releases Met. The polypeptide undergoes partial hydrolysis to give the following peptides. What is the sequence of the polypeptide?

1. Ser, Lys, Trp

2. Gly, His, Ala

3. Glu, Val, Ser

4. Leu, Glu, Ser

5. Met, Ala, Gly

6. Ser, Lys, Val

7. Glu, His

8. Leu, Lys, Trp

9. Lys, Ser

10. Glu, His, Val

11. Trp, Leu, Glu

12. Ala, Met

After the polypeptide shown below was treated with maleic anhydride, it was hydrolyzed by trypsin. (After a polypeptide is treated with maleic anhy- dride, trypsin will cleave the polypeptide only on the C-side of arginine.)

Gly-Ala-Asp-Ala-Leu-Pro-Gly-Ile-Leu-Val-Arg-Asp-Val-Gly-Lys-Val-Glu-Val-Phe-Glu-Ala-Gly- Arg-Ala-Glu-Phe-Lys-Glu-Pro-Arg-Leu-Val-Met-Lys-Val-Glu-Gly-Arg-Pro-Val-Gly-Ala-Gly-Leu-Trp

a. After a polypeptide is treated with maleic anhydride, why does trypsin no longer cleave it on the C-side of lysine?

b. How many fragments are obtained from the polypeptide?

How would a protein that resides in the nonpolar interior of a membrane fold compared with the water-soluble protein just discussed?

Indicate the peptides produced from cleavage by the indicated reagent:

a. His-Lys-Leu-Val-Glu-Pro-Arg-Ala-Gly-Ala by trypsin

b. Leu-Gly-Ser-Met-Phe-Pro-Tyr-Gly-Val by chymotrypsin

A decapeptide undergoes partial hydrolysis to give peptides whose amino acid compositions are shown. Reaction of the intact decapeptide with Edman's reagent releases PTH-Gly. What is the sequence of the decapeptide?

1. Ala, Trp

2. Val, Pro, Asp

3. Pro, Val

4. Ala, Glu

5. Trp, Ala, Arg

6. Arg, Gly

7. Glu, Ala, Leu

8. Met, Pro, Leu, Glu

Which bonds in the backbone of a peptide can rotate freely?

Show the steps in the synthesis of the tetrapeptide in Problem 34, using Merrifield's method.

Why is excess ammonia used in the preceding reaction?

Show how valine can be prepared by

a. a Hell–Volhard–Zelinski reaction.

Show how valine can be prepared by

c. a reductive amination.

Which of the following C-terminal peptide bonds is more readily cleaved by carboxypeptidase A? Explain your choice.

Ser-Ala-Leu or Ser-Ala-Asp

Show how you would synthesize any of the standard amino acids from each starting material. You may use any necessary reagents.

(a)

Show how the following amino acids might be formed in the laboratory by reductive amination of the appropriate α-ketoacid.

(a) alanine