Figure 2.

Calculated Coulomb potential map of thermolysin with the atomic model in this study showing the active site with the zinc ion. The structure is determined from data merged from two nanocrystals. The (2F _obs − F _calc) map is contoured at the 1σ level and is depicted in blue. The residual (F _obs − F _calc) map is contoured at the +3σ level (depicted in green) and the −3σ level (depicted in red). (a) Before correcting for dynamical scattering. (b) After correcting for dynamical scattering. (c) After correcting for dynamical scattering and considering the zinc charge. The positive peak in the residual map that appears in the final model (green arrow) could be attributed to a hydroxy or chloride ion, which bridges the zinc ion and the guanidinium group capping Arg203.