And so what happens is a nearby histidine in the active side participates in actually taking away that H atom. And so we see that the H atom is transferred onto this nitrogen and the positive charge is now essentially delocalized among these different atoms in the histidine side chain. But this one now contains a full negative charge. And now this became a very strong nucleophile. And this can participate in forming covalent, a temporary covalent bond. So as we'll see in the next several lectures, chimetrypsin, which this basically describes, uses not only acid based catalysis but it also uses covalent catalysis in decreasing the activation energy of that particular chemical reaction.