The degree of ligation of T state human haemoglobin crystals is reduced by
inositol hexaphosphate (IHP). The structure of a partially ligated haemoglobin
has been refined using fast Fourier restrained-least-squares techniques. Manual
interventions were required to escape from local minima and introduce a large
number of solvent molecules. Individual isotropic temperature factors were
refined for all atoms and the final average atomic temperature factor is 32.3
A2. The final R factor is 19.6% for all data between 10 and 1.5 A. The final
model consists of 4560 protein atoms and 313 solvent molecules. The occupancies
of the ligand atoms and the anisotropic behaviour of the iron atoms have been
refined, demonstrating that the alpha haem groups are only partially ligated and
that there is no ligation of the beta haems. Density for the IHP indicates that
it is not well ordered even though changes in the ligation and structure of the
haemoglobin indicate its presence.
