The structure of carbon monoxide myoglobin: real-space refinement.

The refinement results in optimum positioning of atoms in the density in most cases, and the juxtaposition of positive and negative density leads to high contrast in the maps and rapid convergence of the refinement. The real-space technique is particularly useful in handling the problem of peak overlap, which is difficult in the neutron case. All refinements to date have been done on the original map, which was phased without hydrogen and deuterium atoms, but the next series of refinements will contain H and D atoms, hydrogen exchange information, and structured water molecules. Comparison of the refinements of CO, Mb and met Mb have shown the iron atom to move nearly into the heme plane. No deuterium atom exists to bond the distal histidine to the CO ligand. Atomic coordinates of all atoms and water molecules will be published on completion of the refinements.