Download Exercise 2

Chemistry 255
Name(s):
Exercise 2 — Peptides
1. Draw the appropriate titration curve for the tripeptide Met-Val-Lys, starting at
pH 1 and ending at pH 12. On the curve label the pKas and the pI. Below the
titration curve, using structures, show the equilibria that occur at the buffering
region(s) and the equivalence point(s).
2. Give the products of a trypsin digestion of the peptide:
his-phe-lys-val-asp-asp-arg-val-val
3. Draw the full structure of the one predominant form of each fragment as it would
exist at pH 7.4. Pay attention to side chains and charges!
4. Indicate the positions of each of the peptide fragments on an isoelectric focusing
gel, and state the pH at that position. Though the pKs of each of the linked residues
differ slightly from pKs of the individual amino acids they originally were, assume that
the values given in table 4.1 are appropriate.
5. Though the peptide in question 2 is not nearly long enough to be a true protein, it
might be part of a protein. Would this peptide prefer to be on the outside of the
protein’s tertiary structure, or the inside? Explain your choice.