Instead, what it does is it forms a shift base between the catalytic lysine residue in the active side of the enzyme and the incoming keto substrate molecule. So to see exactly what we mean, let's actually take a look at the details of the reaction mechanism. So this is the portion of the lysine residue found in the active site of the enzyme, and this is the incoming substrate molecule. So remember, we have two substrate molecules. This is one of them in this step, and this is the second one in this step. So we have the keto substrate molecule, and in this particular case, the keto substrate that we're going to look at is the CETO heptulose seven phosphate.