Question

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19. A peptide is composed of the following amino acids: Ala, Arg. Glu, Gly, Lys, Met, Phe, Ser, Tyn Given the following data deduce the sequence of the peptide. Trypsin digestion yielded two fragments with the following composition: Fragment 1: Ala, Arg, Glu, Met, Phe, Ser Fragment 2: Gly, Lys, Tyr Chymotrypsin digestion yielded three fragments with the listed compositions: Fragment 1: Ala, Gly, Lys, Phe Fragment 3: Arg, Glu, Met, Ser Cyanogen Bromide cleavage yielded two fragments with tht indicated compositions: Fragment 1: Arg, Ser Fragment 2: Ala, Glu, Gly, Met, Phe, Tyr, Lys

Answer 1

Amino acids present in the peptide are:

Ala, Arg, Glu, Gly, Lys, Met, Phe, Ser, Tyr

1. Trypsin digestion gave two fragments:

1 - Ala, Arg, Glu, Met, Phe, Ser

2- Gly, Lys, Tyr

Trypsin cleaves the peptide at C terminal of Lys and Arg

thus fragment 1 is : _ _ _ _ _Arg and fragnemt 2 is: _ _Lys

or Possible arrangements are:

_ _Lys _ _ _ _ _ Arg and _ _ _ _ _ Arg_ _Lys

2. Chymotrypsin digestion gave three fragments:

1 - Ala, Gly, Lys, Phe

2- Tyr

3- Arg, Glu, Met, Ser

Chymotrypsin cleaves the peptide at C terminal of Trp, Tyr and Phe

thus fragment 1 is  _ _ _ Phe

as fragment 2 is Tyr. Means Tyr is at the N-terminal of peptide

Thus polypeptide is like: Tyr _ _ _ Phe _ _ _ _

3. Cyanogen bromide digestion gave two fragments:

1 - Arg, Ser

2- Ala, Glu, Gly, Met, Phe, Tyr, Lys

cyanogen bromide cleaves the peptide at C terminal of Met

the sequence should be: _ _ _ _ _ _ Met_ _

Combining the information we get:

A: Tyr _ _ _ Phe _ Met _ _

from trypsin possible fragments are: _ _Lys _ _ _ _ _ Arg OR _ _ _ _ _ Arg_ _Lys

compairing with A, it is clear that _ _Lys _ _ _ _ _ Arg is correct placement of two peptides

thus we get: Tyr _Lys _ Phe _ Met _ Arg

Now in Trypsin we get a fragmet as : Gly, Lys, Tyr

thus Tyr Gly Lys _ Phe _ Met _ Arg

A fragment of Chymotrypsin gives: Ala, Gly, Lys, Phe

thus: Tyr Gly Lys Ala Phe _ Met _ Arg

A fragment of cyano bromide gives: Arg, Ser

thus: Tyr Gly Lys Ala Phe _ Met Ser Arg

Left out blank will therefore be Glu as

Tyr Gly Lys Ala Phe Glu Met Ser Arg

Therefore the sequence of amino acid is:

Tyr Gly Lys Ala Phe Glu Met Ser Arg