Under most biological conditions, however, histidine is considered to be a triprotic acid. This is due to the pKa of the being .A. nitrogen in the imidazole ring possessing a hydrogen but no charge; much lower than the pH values normally found in a cellB. nitrogen in the imidazole ring possessing a hydrogen but no charge; much higher than the pH values normally found in a cellC. carboxylic acid; much lower than the pH values normally found in a cellD. carboxylic acid; much higher than the pH values normally found in a cell