Chemistry Reference
In-Depth Information
N-terminal amino acid is alanine, the C-terminal one is tryptophan, and the name is
alanylglycylvalyltyrosylcystylphenylalanylleucyltryptophan.
17.50
The linear sequence of vasopressin is:
(N terminus)
Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-Gly (C terminus)
Each of the cysteine amino acid residues has the -CH
2
SH moiety as the R group.
a. In the presence of a mild oxidizing agent (H
2
O
2
), a disulfide linkage will form
between both cysteine residues.
b. The linear form of this short peptide would be less compact than the cyclic form.
Also, relative to the open chain form, the ring formed by the disulfide version would
present the various R groups on the other amino acids in unique ways to other
proteins for regulating biological processes.
17.51
The point of this problem is to illustrate that it is deceptively easy to use the three-
letter abbreviations in designating peptide structures. Although Try-Gly-Gly-Phe-
Met appears quite simple, the full structure is not. With a molecular formula of
C
29
H
36
O
6
N
6
S, this pentapeptide has a molecular weight of 596 and is quite a
complex polyfunctional molecule.
H
O
O
O
H
O
H
O
H
2
N
C
C
NH
CH
2
C
NH
CH
2
C
NH
C
C
NH
C
C
OH
CH
2
CH
2
CH
2
CH
2
CH
3
S
N
H
17.52
The complete hydrolysis tells us what eight amino acids are in angiotensin II.
Reaction with Sanger's reagent indicates that Asp is the N-terminal amino acid.
Partial digestion with carboxypeptidase indicates that Phe is the C-terminal amino
acid. We can now write the following partial structure:
Asp-(Arg, His, Ile, Pro, Tyr, Val)-Phe
Trypsin cleaves peptides at the carboxyl side of Arg and chymotrypsin cleaves
peptides at the carboxyl side of Tyr and Phe. Since we already know that Phe is the
C-terminal amino acid, the chymotrypsin treatment tells us that Tyr is the fourth
amino acid from the N-terminus, and we can write the following partial structure:
Asp-(Arg, Val)-Tyr-Ile-His-Pro-Phe
The trypsin treatment tells us that Arg is the second amino acid from the N-terminus.
Therefore, angiotensin II is:
Asp-Arg-Val-Tyr-Ile-His-Pro-Phe
