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Figure 1.
Figure 1. Stereo view of the final 2mF[o]–DF[c] electron
density map for oxyHbA, showing (a) the ligand at the α haem
and (b) the β chain. In the α subunit, a small peak of density
(roughly 1.5σ) is found about 2.2 Å from the oxygen
ligand and 3.1 Å from Leu29. Leu29 shows some sign of
adopting more than one rotamer, which may allow a partially
occupied water molecule into the haem pocket. Density is
contoured at 1.5σ. It can be seen that the O2 atom of the
ligand, not directly bonded to the haem, is better defined in
the α pocket than in the β haem pocket density. The lower
electron density in the β subunits is indicative of a weaker
bond to the distal histidine and greater rotation about the
Fe–O bond. Temperature factors for the O2 atoms are similar
(35 Å^2and 33 Å^2 in the α and β subunits,
respectively).
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