Question

The peptide Vasopressin is an antidiuretic hormone secreted by the pituitary gland of the brain. It has the sequence:

Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-Gly

A) Write out this sequence in one-letter code
B) Name the C-terminal residue
C) Give the net charge at pH 7
D) Draw the structure of the peptide showing side chains and identifying the peptide bonds

Answer 1

Ans. A. One-letter code: CYFQNCPRG

B. C-terminal residue = Gly (G)

C. Net Charge on peptide at pH 7.0 = 1.997 = 2.0

Calculation: Note: The residues with acidic side chain and C-terminal are written in RED/BOLD. Their corresponding charge is written in columns of “Acidic residues”. Ignore all other charge/values in “black ink”. The sum of charge in “RED ink” is the total –ve charge on the peptide at specified pH.

The residues with basic side chain and N-terminal are written in Blue/BOLD. Their corresponding charge is written in columns of “Basic residues”. Ignore all other charge/values in “black ink”. The sum of charge in “Blue ink” is the total +ve charge on the peptide at specified pH.

The charge on each residue/ group is calculated using Henderson-Hasselbalch equation as shown in respective column.

#D.