And so this is also resonant stabilized, just like the argument, because this is essentially an aromatic ring. Now, the thing about histidine, because it contains a lower PKA, and because it can be protonated or deprotonated at the physiological PH, this is a very common amino acid that exists in the active sites of enzymes. Remember, an enzyme is a biological catalyst that speeds up different reactions, and the active side is the location on that enzyme where that reaction actually takes place. So histidine is very commonly found in the active sites of many different enzymes, as we'll see in our study of biochemistry. So we have Lysine and Arginine, which are always positively charged on their side chain groups at the physiological PH of seven, histidine, which is also basic, like Lysine, Arginine. But the thing about HistoGene is it can either be positively charged or neutral at the normal physiological PH.