Question: histidine has ionizable groups with pka?
Answer: Histidine has ionizable groups with pKa values of 1.8, 6.0, and 9.2, as shown below. A biochemist makes up 100 mL of a 0.100 M solution of histidine at a pH of 5.40. She then adds 40 mL of 0.10 M HCl.