Fig. 5. Environment of proposed catalytic water (shown with
heavy black bonds). (a) Nuclear density (2F[o] – F[c]). (b)
Atomic arrangement in the 1.8-Å-resolution neutron map.
Both diagrams show the water molecule (with an elongated shape
indicating two protons) and the two metal ion-carboxylate-water
motifs. In the electron-density map (data not shown), two
possible conformations exist for Asp-257, one of which agrees
with the nuclear-density results shown here.