Schiff base
The active site contains the zwitterionic pair Glu-45/Lys-133. The Lysine, which is involved in the formation of the Schiff base is coordinated by a phosphate ion and two solvent water molecules. The first water molecule serves as a shuttle between the Glutamate and the substrate, staying bound to the enzyme throughout the catalytic cycle. The second water molecule is a product of the dehydration of the carbinolamine that leads to the formation of the Schiff base. It also functions as the nucleophile during hydrolysis of the enzyme-product Schiff base, leading to the release of pyruvate.