Cleavage of a polypeptide by CNBr and chymotrypsin yielded fragments with the fo

Question

Cleavage of a polypeptide by CNBr and chymotrypsin yielded fragments with the following amino acid sequences:

CNBr treatment:

1. Arg-Ala-Tyr-Gly-Asn

2. Leu-Phe-Met

3. Asp-Met

Chymotrypsin

4. Met-Arg-Ala-Tyr

5. Asp-Met-Leu-Phe

6. Gly-Asn

a). What is the sequence of the intact polypeptide? Please show the sequence in one-letter abbreviations.

b). Please draw the structure of the first CNBr peptide.

c). Does this peptide absorb ultraviolet light? Explain.

d). If you cleave this peptide with trypsin, what fragments you will get?

e). Please estimate the molecular weight of this peptide.

Explanation / Answer

a) Intact polypeptide CNBr treated : Arg-Ala-Tyr-Gly-Asn-Leu-Phe-Met-Asp-Met.

CNBr cleaves from the C-terminal of methionine.

Intact polypeptide Chemotrypsin treated : Met-Arg-Ala-Tyr-Asp-Met-Leu-Phe-Gly-Asn

Chemotrypsin cleaves from the C terminal of aryl amino acids like Phe or Tyr.

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