The tripeptide +H3N-Leu-His-Glu-COO- has pKa  values of 2.2, 3.6, 6.0 and 9.1.  The  isoelectric point (pI) for this peptide will be

1. Draw the appropriate titration curve for the tripeptide Met-Lys-Val starting at pH 1 and ending at pH 12. Label the pKas and the pI. Draw the two different forms of the molecule that is present at each buffering region. 2. Draw the structure of the peptide Arg-Met-His-Val-Glu and circle the coplanar atoms in one peptide bond. 3. Determine the pI for the peptide given in question 2 above.

H CH₂ H₂C HC-CH3 CH₂ H H₂C (S) H₂C H CH₂ CH₂ CH₂ NH O C NH NH₂ a) Which of the following statements about this peptide are correct? Group of answer choices Treatment of this peptide with trypsin generates two products. This peptide is a substrate for carboxypeptidase A Treatment of this peptide with cyanogen bromide generates a pentapeptide and a tripeptide. Treatment of this peptide with chymotrypsin generates three products. Treatment of this peptide with elastase generates 2 products. None of the above statements are correct. b) What is the sequence of this peptide using one letter abbreviations? c) What is the pH which would correspond to the ionization of the peptide as drawn above? 1, 5, 7, 10, 14

Draw a schematic of the chemical structure of the Leu-Tyr-Met-Lys tetrapeptide, with the correct ionization at neutral pH (pH 7). Also, give an estimate the pl of this tetrapeptide (you are given that the pKa of any acidic R group is 4, the pKa of any basic R group is 11.5, and the pKa of the α-COOH is 2, and the a-NH3 is 9.5). Provide rationale!