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. And this stimulates the removal of a hydrogen ion from the methyl group by aspertain 375. So together, these residues act on this acetyl coenzyme A and allows the formation of that enol intermediate molecule that now contains that pi bond between these two carbons of the acetyl group. Now, let's move on to four and five.