Acid dissociation reaction for E-amino group (side chain of Lys): (R)E-NH3+ # (R)E-NH2 + A. For a weak acid such as the side chain &-amino group of a lysine residue in a protein, if the pKa of that specific residue's E-amino group is exactly 10.0, in an environment in which the pH = 9.0, what would be the ratio of base to acid ( [ε-NH2]/[ε-NH3+1 )?