Although tryptophan contains a heterocyclic amine, it is considered a neutral amino acid. Explain why the indole nitrogen of tryptophan is more weakly basic than one of the imidazole nitrogens of histidine.

Draw the structure of the predominant form of

(e) a mixture of alanine, lysine, and aspartic acid at (i) pH 6;

Draw the structure of the predominant form of

(a) isoleucine at pH 11.

Draw the structure of the predominant form of

(d) glutamic acid at pH 7.

Draw the structure of the predominant form of

(e) a mixture of alanine, lysine, and aspartic acid at (iii) pH 2.

Aspartame (Nutrasweet®) is a remarkably sweet-tasting dipeptide ester. Complete hydrolysis of aspartame gives phenyl alanine, aspartic acid, and methanol. Mild incubation with carboxypeptidase has no effect on aspartame. Treatment of aspartame with phenyl isothiocyanate, followed by mild hydrolysis, gives the phenylthiohydantoin of aspartic acid. Propose a structure for aspartame.

Draw the following amino acids in all possible protonation states as you move from high pH to low pH.

b. His

Draw the electrophoretic separation of Ala, Lys, and Asp at pH 9.7.

Predict the predominant form and net charge of tyrosine (Y) at pH 10. What is the net charge?