(b) When this peptide was digested by CNBr (which cuts the carboxyl side of Met)

Question

(b) When this peptide was digested by CNBr (which cuts the carboxyl side of Met), two fragments were obtained with the following sequences; Val-Lys-Thr-Phe-Gly-Arg Ala-Arg-Glu-Met Using the oxerlap peptides, determine the entire amino acid sequence of this peptide. Bonus. (10 pts) Answer each of the following questions regarding the tripeptide Asp-Cys-Ala Aspartic acid Cysteine Ala 1.99 1.92 2.35 9.90 10.78 9.87 3.30 8.33 a) Name the amino-terminal residue. b) Give the net charge at pH 1. Explain. c) Give the net charge at pH 12. Explain.

Explanation / Answer

B) As the peptide was cut by CNbr and it cuts at the C terminal of met then the met has to be in middle because then only it can produce 2 fragments.

So the sequence is

Ala arg glu met val cys thr phe gly arg.

Bonus

a) Amino terminal residue is Aspartic acid.

b) The charge will be +1 at pH 1 because amino terminal will be protonated and all the carboxylic group will have 0 charge.

C) The charge will be -3 at pH 12 because amino group will be deprotonated and aspartic acid has two carboxyl group that will be deprotonated and C terminal will also be deprotonated and because three carboxylic groups are deprotonated the charge will be -3.

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