A) Estimate the net charge of a Glu-Tyr dipeptide at pH 6.0.
B) Estimate the net charge of an Asp-Asp-Asp tripeptide at pH 7.0.
C) Estimate the net charge of a His-Lys-Glu tripeptide at pH 8.0.
N-terminal amine group (α-amino): pKa ≈ 9.0
C-terminal carboxyl group (α-carboxyl): pKa ≈ 2.0
Glutamate (Glu) side chain (γ-carboxyl): pKa ≈ 4.1
Tyrosine (Tyr) side chain (phenol group): pKa ≈ 10.1
Histidine (His) side chain (imidazole, pKa ≈ 6.0)
Aspartate (Asp) side chain carboxyl groups (β-COOH, pKa ≈ 3.9 for each Asp residue)
Lysine (Lys) side chain (ε-amino, pKa ≈ 10.5)