Another strategy to account for the missing electronic polarization in fixed charge force fields is to use scaled charges, which is formally equivalent to including the electronic polarization as a dielectric continuum. This mean-field theory, called Electronic Continuum Correction (ECC), prescribes scaling all ionic charges by a factor 1/ √ ϵ ∞ ≃ 0.75, and has been shown to improve the description of ion-protein and ion-phosphate interactions. Using ECC force fields for the active site Mg 2+ ions considerably improved the active site stability, with a stable structure over 500 ns in 2 of the 4 replicas. Using it for all charged 13 residues in the active site even further stabilizes the structure (see Figure ).