Determining Amino Acid Sequence

[Myelinated-Man]

1. A peptide (compound A) was hydrolysed and found to contain equimolar quantities of arg, val, tyr, glu, lys, ala and gly.

 

(a) Exhaustive treatment of compound A with trypsin yields the following compounds:

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.

(b) Short-term treatment of compound A with carboxypeptidase yields free glycine as the first detectable amino acid.

© N-terminal analysis of compound A with FDNB yields DNP-alanine in the ether phase extracted from the acid hydrolysate.

 

What is the sequence of the peptide?

 

Given this info, the N-terminal AA is alanine, and the C-terminal AA is glycine. Not sure where to go from here, as am very new to the topic.

 

2. Acid hydrolysis of 1 mmol of a pentapeptide yields 2 mmol of glutamic acid, 1 mmol of lysine and no other amino acids. Trypsin splits the original pentapeptide into two fragments. Upon electrophoresis at pH 7.0, one of the fragments moves towards the anode and the other towards the cathode. Treatment of one of the tryptic fragments with FDNB, followed by acid hydrolysis yields DNP-glutamic acid. Treatment of the original peptide with chymotrypsin yields two dipeptides and free glutamic acid.

 

Give an amino acid sequence for the pentapeptide that is consistent with the foregoing data.

 

No clue.

[CharonY]

For both questions first check how trypsin and chymotrypsin cleave proteins/peptides.