All amino acids have two ionizable functional groups: an α-amino group (average pKa of 9.4) and an α-carboxylic acid group (average pKa of 2.2). Lysine also has an ionizable side chain (R group) with a pKa of about 10.5. One of the possible ionization states of lysine is shown in the image.
At what pH would the structure be the predominant ionization state? Consider the ionization state of all three of the functional groups.
The protonated form of the R group of lysine is shown in the structure. The ratio of the charged (protonated) form to the deprotonated form depends on the pKa of the R group and the pH of the solution. Select all the pH values at which the charged form of the R group would predominate.
2.2
10.5
11.6
4.2