Several tests were performed on a tripeptide. Below, state what you can determin

Question

Several tests were performed on a tripeptide. Below, state what you can determine about the structure of the tripeptide from each of the tests. Finally, provide the sequence of the tripeptide. A) When reacted with fluorodinitrobenzene (FDNB) and hydrolyzed to completion, the mixture contained dinitrophenyltryptophan. From this I can conclude B) Limited digestion with carboxypeptidase released threonine. From this I can conclude: C) This peptide had no net charge after addition of one mole equivalent of HCl. From this I can conclude: D) Amino acid analysis revealed that this peptide contained no asparate or asparagine From this I can conclude: E) The single letter amino acid sequence of this peptide is

Explanation / Answer

A) Flurodinitrobenzene is used to determine the N terminal amino acid. Here, after reaction with FDNB, mixture contains diphenyltryptophan. From this we can conclude the N terminal amino acid is tryptophan.

B) Limited digestion with carboxypeptidase releases threonine. So, the C terminal amino acid is threonine.

C) No charge left after addition of one mole of HCl. Therefore, the tripeptide must contain negative amino acids like aspartic acid and glutamic acid.

D) Peptide does not contain asprtate or asparagine. So, the negative amino acid is glutamate or glutamic acid.

E) Amino acid sequence is N terminus-tryptophan-glutamate-threonine-C terminus

Single letter amino acid sequence is N terminus - W-E-T - C terminus.

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