Questions with Answers- Proteins & Enzymes
A.
A peptide with 12 amino acids has the following amino acid composition:
2 Met, 1 Tyr, 1 Trp, 2 Glu, 1 Lys, 1 Arg, 1 Thr, 1 Asn, 1 Ile, 1 Cys
Reaction of the intact peptide with fluorodinitrobenzene followed by acid hydrolysis creates a
derivative of Ile.
A specific cleavage of the intact peptide produces fragments with the following sequences:
Glu-Cys-Asn-Met-Lys
Met-Glu-Thr-Arg-Trp
Ile-Tyr (Questions 1-5)
1._____ Which reagent was used for the specific cleavage?
a)
chymotrypsin
b)
trypsin
c)
V8 protease
d)
cyanogen bromide
2._____ Which amino acids would be released when the intact peptide was treated first with
V8 protease followed by treatment with cyanogen bromide?
a) Glu and Met
b)
Glu and Lys
c) Met and Lys
d) Glu, Met, and Lys
3._____
Which treatment would result in the release of Lys and Arg from the intact peptide?
a) trypsin
b) trypsin followed by dansyl chloride
c) trypsin followed by carboxypeptidase
d) trypsin followed by mild acid
4._____
If this intact peptide is sequenced using the Edman degradation, which step will
be part of the procedure?
a)
The Edman reagent will react with all 12 amino acids simultaneously.
b) Lithium borohydride will react with an
α
-carboxyl group.
c)
Phenylisothiocyanate will react with an
α
-amino group.
d)
Strong acid will be used to cleave off one modified amino acid.
5._____
If this peptide is normally part of a multimeric protein composed of four identical
subunits, what procedure might be needed prior to performing the Edman
degradation?
a)
The four subunits should be separated and sequenced individually.
b)
Two specific cleavages should be done to create two sets of fragments.
c)
Peptide bonds should be broken using hydrazine.
d)
Disulfide bonds should be reduced with mercaptoethanol.
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