Determine the amino acid sequence. Make sure you write your sequence in the prop

Question

Determine the amino acid sequence. Make sure you write your sequence in the proper orientations.

Complete acid hydrolysis of the protein gives the following composition: Asp, Arg, Cys, Ile, Met, Phe, Pro, Tyr

Trypsin digestion yields a hexapeptide containing (Cys, Ile, Met, Phe, Pro, Tyr) and a dipeptide containing Asp and Arg.

Reaction with NCBr yields a dipeptide of Phe and Pro, and a hexapeptide of all the others.

Chymotrypsin digestion yields two peptides of composition (Asp, Arg, Cys, Tyr) and (Ile, Met,

Phe, Pro).

The (Phe, Pro) dipeptide cannot be cleaved by carboxypeptidase A.

Explanation / Answer

Based on the given data, the peptide has eight amino acids. Based on the Trypsin digestion, we know that Asp and Arg are linked with peptide bound. Thus, dipeptide with polarity is: Arg- Asp.

Based on the reaction with CNBr, we know that Phe and Pro are linked with peptide bound. Thus, Phe-Pro (it cannot be cleaved by carboxypeptidase A), so this dipeptide is not at carboxy-terminal. Based on the CNBr action this peptide is present after Met, so peptide sequence is:

Cys-Arg- Asp-Tyr-Phe-Pro Met-Ile

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