Extended X-ray absorption fine structure determination of iron nitrogen distances in haemoglobin.

EXAFS spectra have been obtained of oxy and deoxy complexes of haemoglobin and of the 'picket fence' porphyrin, using synchrotron radiation as a source of X rays. The fluorescence data were Fourier filtered to obtain distances to the first shell and corrections applied to remove contributions from the axial ligands. In this way, the iron to porphinato nitrogen distances were determined to be 1.98 +/- 0.01 A for both oxygenated complexes and 2.055 +/- 0.01 A for both deoxy forms.