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    Determining the sequence of a peptide after digestions

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    A.In trying to identify the amino acid sequence of the plant hormone of a 12-mer peptide;
    The following were found:
    1.One of the chymotrypsin digestion products was identified as RGDTY
    2.Trypsin digestion of the 11-mer peptide gives GQLFR and another 6-mer peptide
    3.Cyanogen Bromide (CNBr) gives an 11-mer peptide and homserine lactone
    4.Carboxyl peptidase C first released Glu and then released Ile, then Tyr
    Identify the sequence of this peptide?

    B.When cysteine is treated with bromoethylamine (BrCH2CH2NH3+), the resulting modifies side chain can be recognized by trypsin.
    DRAW the structure of the modified side chain of cysteine by bromoethylamine and EXPLAIN WHY trypsin can recognize it?

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    Solution Preview



    YIE must be the last 3 amino acids due to the carboxypeptidase C treatment, which indiscriminately cleaves the c-terminal residue.

    Since trypsin cleaves only one time, there must be only one Arg or Lys residue, meaning that the Arg residue found in the chymotrypsin and the trypsin digests must be ...

    Solution Summary

    In this solution we explore how to determine the primary sequence of a peptide given the products that appear when we treat with enzymes, including trypsin, chymotrypsin, and carboxypeptidases. In the second part of the question, a modification to cysteine residues (treatment with bromoethylamine) is considered.