2. An amino acid with three ionizable functional groups can exist in different forms and histidine is an example. [17 pts.] (a) Draw the structures of the predominant ionization state of histidine at pH 1, 4, 8 and 12. Include the net charge on the histidine molecule in each ionization state. (b) Write the equilibrium equations for the three ionizable protons present in histidine an assign the proper pKa for each ionization.