Fig. 2. Active sites of Pfk-2 in chains (a) D and (b) B, containing F6P and FBP, respectively. In (a) the electron density omit map (F_o–F_c) contoured at 2σ for F6P and both MgATP^2– is shown in blue (where ATP_S is the substrate ATP and ATP_A is the allosteric ATP). Residues surrounding F6P are represented. In (b) the corresponding electron density omit map for FBP and MgADP^– is shown in blue. Residues surrounding FBP are represented. The arrows indicate the Mg²⁺ ions positions.