Fig. 3. Schematic representation of possible reaction mechanisms catalyzed by Pfk-2. The arrows indicate the possible paths. Starting for the reactants (upper left corner), the reaction could proceed from: (i and ii) a proton transfer (to both Asp256 or γ-phosphate) followed by a phosphate transfer or (iii) by a phosphate transfer followed by a proton transfer. Blue arrows indicate proton transfer events and green arrows indicate phosphate transfer.