The Glycolytic Enzymes

In the ninth step of glycolysis, the cell places the phosphate in an uncomfortable position, making it easy to remove to form ATP. The enzyme enolase removes a water molecule, forming a new double bond in an awkward place in the carbon skeleton of the molecule. PDB entry 2one is a remarkable structure that shows both sides of this reaction, before and after the water is removed. The enzyme contains two identical active sites, shown below, and the crystal structure has captured a different state in each of the active sites. The left image shows the molecule before the reaction has started and the right image shows the molecule after the water has been removed. Enolase uses two metal ions in its reaction. The first is a magnesium ion in this structure, colored light blue here. It anchors the molecule to the enzyme, holding it in the proper place. The second ion then binds and assists with the catalysis. In this structure, a lithium ion was found in one of the active sites in this location. A perfectly-placed histidine also assists in the reaction.