Organic Chemistry 354 Open Book Quiz - December 2, 1999
Dr. Sundin
- 1. The antibiotic Syringomycin contains a nonapeptide. In addition to the
common amino acids, it also contains derivatives, Dab and Dhb, of
a-aminobutyric acid. Determine its amino acid
sequence based on the analytical data below.
- Complete hydrolysis: Arg = 1; Asp = 1; Dab = 2; Dhb = 1; Phe= 1; Ser = 2;
Thr = 1.
- Edman degradation gave Ser. Carboxypeptidase A gave Thr. Partial hydrolysis
gave a complex mixture from which only four tripeptides (see below) were isolated
in high enough yield and purity to be characterized. They are:
Arg-Phe-Dhb
Dab-Arg-Phe
Dhb-Asp-Thr
Ser-Dab-Dab
Answer
- 2. In solution at a pH of 5.97, Glycine (Gly) has a net charge of zero.
However, at a pH of 2 Gly has a net charge of +1 while at a pH of 11 Gly
has a net charge of -1.
- a. Give the detailed structure of the predominant species at each pH value.
Answer
- b. Peptides also exhibit different net charges at different pH’s.
For each of the following tripeptides, determine the net charge (it will be
either +3, +2, +1, 0, -1, -2, or -3) at pH’s of 2 and 11.
- 1. Asp-Glu-Ala at pH = 2 at pH = 11
Answer
- 2. Asp-His-Glu at pH = 2 at pH = 11
Answer
- 3. Leu-Pro-Ser at pH = 2 at pH = 11
Answer
- 3.Give the detailed structure of Asp-Glu-Ala.
Answer
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