All amino acids have two ionizable functional groups: an c-amino group (average pk, of 9.4) and an a-carboxylic acid group (average pk of 2.2). Arginine also has an ionizable side chain (R group) with a pK, of about 12.5. One of the possible ionization states of arginine is shown. HNCH-C-OH 1 CH2 CH2 CH NH C=NH NH At what pH would the structure be the predominant ionization state? Consider the ionization state of all three of the functional groups. 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 arginine is shown in the structure. The ratio of the charged (protonated) form to the deprotonated form depends on the pK, 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. 7.4 0 5.3 13.5 12.5