6. (15 pts) Determine the amino acid sequence of a polypeptide from the followin

Question

6. (15 pts) Determine the amino acid sequence of a polypeptide from the following data. Show and explain your work Complete hydrolysis of the peptide yields Ala, Arg, Gly, 2 Lys, Met, Phe, Pro, 2 Ser, Tyr, and Val. Treatment with Edman's reagent release PTH-Val Carboxypeptidase A releases Ala Treatment with cyanogens bromide yields the following two peptides 1. Ala, 2 Lys, Phe, Pro, Ser, Tyr 2. Arg, Gly, Met, Ser, Val Ticiment sidh rywinils th alowing fphe pepider 1. Gly, Lys, Met, Tyr Treatment with chymotrypsin yields the following three peptides: 1.2 Lys, Phe, Pro 3. Arg, Ser, Val 2. Arg, Gly, Met, Ser, Tyr, Val 3. Ala, Ser

Explanation / Answer

in peptide sequence we write amino acids from N-terminal to C-terminal (left to right)

first we treat peptide with edman's reagent & PTH -Val is released out.... as we know edman's reagent is used for N-terminal analysis so first amino acid is val from N-terminal

val _ _ _ _ _ _ _ _ _ _ _

then carboxypeptidase A release Ala..... carboxypeptidase A is C-terminal exopeptidase which is used to cleave all amino acid except arg, lys, pro if proline is not next residue, so ala is last residue in peptide chain at C-terminal

val _ _ _ _ _ _ _ _ _ _ _ ala

when we treat with cynogen bromide, we get two fragments of peptides, cynogen bromide cleave at met on C-terminal. so in given peptide fragments one will have ala in the last & other will have met in the last

_ _ _ _ _ _ ala;                 val ,_ _ _ _, met

now treating with trypsin yields 3 fragments, trypsin cleave at lys, arg on C-terminal,if proline is not next residue, so in given peptide fragments one will have lys in the last & other will have arg in the last & 3rd fragment will have ala(as ala is last c-terminal amino acid) in the last.

_ _ _ lys;       _ _ _ _ ala;     val (1st aa), ser, arg

when we trat with chymotrypsin yields 3 peptides, chymotrpsin clave at phe, trp, tyr on C-terminal,if proline is not next residue, so in given peptide fragments one will have phe in the last & other will have tyr in the last & 3rd fragment will have ala(as ala is last c-terminal amino acid) in the last.

_ _ _ phe;          _ _ _ _ _tyr;         ser, ala

so after doing all tratment and arranging all result we find following amino acid sequence from N-terminaus to C-terminaus as-

val, ser, arg, gly, met, tyr, lys, lys, pro, phe, ser, ala

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