A major contributor to the pronounced field at this site is the presence of the neighboring His195 residue, due to the strong partial negative charges on the N atoms in its imidazole ring pointing towards the FeMoco. As indicated before (cf. Figure ), the protonation state of this residue has been the cause of significant controversy: both a (neutral) mono-protonated form, with the proton on either the e or d site of the imidazole ring, as well as a di-protonated, cationic form (imidazolium), has been suggested for this residue at different stages of the catalytic mechanism. In Figure , we assumed this residue to be in its e mono-protonated form, as this is the experimentally determined protonation state of the resting E0 state, and calculations by Bjornsson and co-workers suggest that it is likely also the most stable one in the E4 state, i.e., right before N2 coordination. Remarkably, our calculations reveal that, in qualitative terms, the electrostatic environment around the FeMoco is fairly robust with respect to changes in the His195 protonation state. For the alternative d form, the FZ is enhanced further by a significant margin, reaching values as high as -2.8 VÅ -1 (Figure ). For the di-protonated form, the direction of the OLEF is reversed in the region around the introduced protons on His195 (locally reaching values as high as +1.5 VÅ -1 ), but it nevertheless retains a non-negligible negative direction, with magnitudes up to -0.7 VÅ -1 , in all the other directions surrounding the Fe2 site (Figure ). Interestingly, upon excluding the charges stemming from the adjacent His195 during the electric field calculation altogether, an almost uniform negative electric field is computed in all directions around the Fe2 site away from the FeMoco, with the OLEF reaching magnitudes up to -0.6 VÅ -1 (Figure ). Furthermore, the attenuation of the field's magnitude with distance is remarkably small. This is reflected by the size of the quivers in the first ring around Fe2, which have nearly the same size as those in the outer ring. This highlights the fact that the field is not caused exclusively by a handful of charges in close proximity to the FeMoco, but that it is in fact a large collection of distant charges/dipoles that contribute to the overall OLEF (cf. Eq. 1; if 𝑟 ! is already big for most 𝑖 at the outer evaluation radius around the metal site, then the field strength is barely reduced by increasing the distance from the edge of the protein by 1.5 Å, to reach the inner evaluation radius).