4. A pentapeptide was found to have the sequence) Aa pentapeptide s reagent, folloposition (not
sequence) Ala Arg Gly Pro Trp. Reaction of the s, gave the DNP derivative of proline. Treatment
of the pentapeptide a aproduced alanine. Treatment of the pentapeptide with trypsin gave a
tetrapeptide hat is the sequence of the pentapeptide? (Spts) which, when treated with
chymotrypsin, produced a tripeptide. W tide. However, after treating it with 5. A student isolated
a protein and assumed it was made up of a single polypep excess dithiothreitol (DTT; see
structure below), two polypeptides were obtained. One of the polypeptides contained 78 amino
acids and the other contained 125 amino acids. Both polypeptides contained 1 Cys and 1 Met
Using the structure of DTT below, sketch what the protein likely looked like before treatment
with DTT (label/name any key amino acids and the ends of your polypeptide). (2pts) A. B. Now,
draw/sketch ALL of the likely products of the reaction labeling/naming any key amino acids.
(3pts) Protein?? Products?? HO DTT
Solution
Ans 4. The sequence of peptide is (N ter)Pro-Gly-Trp-Arg-Ala(C ter)
Sanger\'s reagent reacts with free amino group of N terminal amino acid residue of a peptide and
form a DNP derivative which is released from peptide by hydrolysis. So DNP derivative of
proline indicates that Pro is the first residue at N terminus.
Carboxypeptidases cleaves C terminus amino acid residue, So Ala generation indicates that it is
the first residue at C terminus of peptide.
Trypsin cleaves at carboxyl side of Lys and Arg but the next residue should not be Pro. Hence in
this sequence Arg should be at 4th position from N terminus so that after treatment with trypsin,
it results in a tetrapeptide by cleaving bond between Arg-Ala.
Chymotrypsin cleaves at carboxyl side of aromatic amino acid residues but the next residue
should not be Pro. Hence Trp should be present next to Arg so that after treatment it can results
in a tripeptide formation.
sequence) Ala Arg Gly Pro Trp. Reaction of the s, gave the DNP derivative of proline. Treatment
of the pentapeptide a aproduced alanine. Treatment of the pentapeptide with trypsin gave a
tetrapeptide hat is the sequence of the pentapeptide? (Spts) which, when treated with
chymotrypsin, produced a tripeptide. W tide. However, after treating it with 5. A student isolated
a protein and assumed it was made up of a single polypep excess dithiothreitol (DTT; see
structure below), two polypeptides were obtained. One of the polypeptides contained 78 amino
acids and the other contained 125 amino acids. Both polypeptides contained 1 Cys and 1 Met
Using the structure of DTT below, sketch what the protein likely looked like before treatment
with DTT (label/name any key amino acids and the ends of your polypeptide). (2pts) A. B. Now,
draw/sketch ALL of the likely products of the reaction labeling/naming any key amino acids.
(3pts) Protein?? Products?? HO DTT
Solution
Ans 4. The sequence of peptide is (N ter)Pro-Gly-Trp-Arg-Ala(C ter)
Sanger\'s reagent reacts with free amino group of N terminal amino acid residue of a peptide and
form a DNP derivative which is released from peptide by hydrolysis. So DNP derivative of
proline indicates that Pro is the first residue at N terminus.
Carboxypeptidases cleaves C terminus amino acid residue, So Ala generation indicates that it is
the first residue at C terminus of peptide.
Trypsin cleaves at carboxyl side of Lys and Arg but the next residue should not be Pro. Hence in
this sequence Arg should be at 4th position from N terminus so that after treatment with trypsin,
it results in a tetrapeptide by cleaving bond between Arg-Ala.
Chymotrypsin cleaves at carboxyl side of aromatic amino acid residues but the next residue
should not be Pro. Hence Trp should be present next to Arg so that after treatment it can results
in a tripeptide formation.
