What is the sequence for the following HEXAPEPTIDE? (10 points) • be sure to pro

Question

What is the sequence for the following HEXAPEPTIDE? (10 points) • be sure to provide WORK/ANSWER for Points B-F!

Observations from Sequencing Experiments

A. amino acid content: Y, R, M, K, G, D

B. Reaction with 1-fluoro-2,4-dinitrobenzene yielded DNP-G.

C. Treatment with chymotrypsin yielded two tripeptides.

D. Treatment with trypsin yielded three dipeptides.

E. Treatment with carboxypeptidase yielded methionine.

F. N-terminal sequencing of one the chymotrypsin-produced tripeptides yielded DNP-K.

Explanation and Summary of Protein Sequencing Techniques

1. 1-fluoro-2,4-dinitrobenzene (DNFB) is used to identify the N-terminal amino acid of a peptide, and provides the following product: DNP-AA (where AA = the N-terminal amino acid of the peptide).

2. Trypsin is an enzyme that cleaves a peptide at the C-terminal side of R and K.

3. Chymotrypsin is an enzyme that cleaves a peptide at the C-terminal side of F, Y, and W.
4. Carboxypeptidase is an enzyme that cleaves off the C-terminal amino acid of any peptide.

Explanation / Answer

(C terminal)        M            D            K          Y              R             G    (N terminal)

Since 1-fluoro-2,4-dinitrobenzene (DNFB) is used to identify the N-terminal amino acid of a peptide, N terminal of the hexapeptide is G. it is given that N-terminal sequencing of one the chymotrypsin-produced tripeptides yielded DNP-K. Therefore one of the tripeptide say first one has K as N terminal residue making K the third amino acid. Chymotrypsin is an enzyme that cleaves a peptide at the C-terminal side of F, Y, and W and it yielded two tripeptides therefore it will be on position 4. Carboxypeptidase is an enzyme that cleaves off the C-terminal amino acid of any peptide and it yielded methionine. Therefore M occupies the first position. Since Trypsin is an enzyme that cleaves a peptide at the C-terminal side of R and K and treatment with trypsin yielded three dipeptides, D will occupy the second position and R will occupy the fifth position.

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