Plot of Fe–W1 distance as a function of X-ray dose from the two measured MSS series. The SFX structure determined using SACLA is plotted as the zero-dose point (magenta). The elongation of the bond length with dose is well fitted by a linear function (red line). The deviation at higher doses is associated with a dissociation of W1 from the immediate vicinity of the heme Fe. The extrapolation to zero dose (dashed red line) gives a value of 2.37 (±0.05) Å which is very close to the 2.40 (±0.13) Å value of this parameter in the SFX structure. Error bars shown are the estimated standard uncertainty in bond length obtained from the DPI value of the Fe and W1 atoms (see Materials and methods).