So HistoGene 274 uses the hydrogen ion attached onto this nitrogen. It donates that H ion onto the oxygen of this carbonyl group shown here. And what that does is it weakens this double bond between the carbon and the oxygen at the same time as pertain 375 basically acts as a base and it takes away the H ion from the methyl group shown here. And by taking away the H ion, it allows this sigma bond to basically go on and form a pi bond, displacing these two electrons, allowing those two electrons to take that H ion. And so we see that these two catalytic residues essentially allow the formation of the enormity, the double bond that will act as a nucleophile in the next step, as we'll see in just a moment. So in one we have histidine 274, shown here in the acticide, is used to give the carbonyl oxygen that H plus ion.