This is an aldos because we have an H and a carbon atom attached to the carbon of the carbonyl. Now, that's the general idea of what happens, but what exactly happens within the active side of this enzyme? So let's take a look at the following four picture diagrams. So let's begin with diagram one. Now, if we go into the active side of this enzyme, we'll basically see a bunch of these alpha beta barrels. So we'll see these structures, and in the active side, there are basically two catalytic residues that catalyze this reaction and they catalyze via an acid base reaction.