Question

A peptide (compound A) was hydrolyzed and found to contain equimolar quantities of Arg, Val, Tyr, Glu, Lys, Ala, and Gly.

When compound A is treated with trypsin, the following compounds are produced: Arg, Ala-Lys, and a peptide (Compound B) containing Glu, Gly, Tyr, and Val. Treatment of Compound B with chymotrypsin yields Val-Tyr and Glu-Gly

Short term treatment of Compound A with carboxypeptidase yields free Gly as the first detectable amino acid.

N-terminal analysis of Compound A with FDNB (the same thing you did in lab) yields DNP-Ala (FDNB-Ala derivative) in the ether phase extracted from the acidified acid hydrolysate.

What is the sequence of the peptide from (Compound A)?

Answer 1

Sequence is as shown:

Ala-Lys-Arg-Val-Try-Glu-Gly

1. Action of FDNB(Fluoro-2,4-dinitrobenzene) shows that N- terminal is Ala by formation of DNP-Ala

2. Action of carboxypeptidase shows that C- terminal is Gly.

As carboxypeptidases acts on terminal carboxylic group and hence Gly separates.

3. When trypsin acts, it cleaves peptides chain at carboxylic end of Lys and Arg.

Ala-Lys-Arg-Val-Try-Glu-Gly = Ala-Lys+ Arg+ Compound B

4. Chymotrypsin cleaves N - terminal to the bond of Try.

Val- Try-Glu-Gly=Val-Try+Glu-Gly.