Difference Fourier refinement of metaquohemerythrin

A model for metaquohemerythrin from Themiste dyscritum has been refined in the crystallographic sense of the term by difference Fourier methods at 2.8 and 2.5 Å resolution. Fourteen cycles of refinement reduced R from an initial value of 0.385 for the 9461 reflections from 10 to 2.8 Å to 0.253 for 16 363 reflections from 10 to 2.5 Å resolution. On the basis of peaks in difference maps, 49 water molecules have been added to the model for a total of 3833 atoms in the asymmetric unit.