I'm working on an enzyme mechanism where I start with a histidine at a net charge of zero. In the first step, histidine takes a proton from water (giving histidine a +1 charge). At the end of the reaction, histidine is still protonated and one of my products is a carboxylate. Would the carboxylate attack histidine's proton, giving me a carboxylic acid and a deprotonated histidine? The pKa for my carboxylate is around 3, while histidine has a pKa around 6, so I was unsure whether that would prevent the attack from occurring.