Stereochemistry of iron in deoxyhaemoglobin
Abstract
X-ray crystallography has shown that in deoxyhaemoglobin the iron atoms are displaced by 0.56+/-0.03 Å from the mean porphyrin plane, whereas in liganded haemoglobins they lie either in or close to that plane1,2. Perutz3 proposed this shift as one principal factor responsible for haem-haem interaction. Eisenberger et al. used extended X-ray absorption fine structure (EXAFS) to measure the Fe-N distance in deoxyhaemoglobin and concluded that the irons lie only 0.2+0.1-0.2 Å from the plane of the porphyrin nitrogens and that the mechanism of Perutz is therefore invalid4. We have now compared the EXAFS of deoxyhaemoglobin with that of the ferrous `picket fence' 2-methylimidazole complex in which the displacement of the iron from the plane of the porphyrin nitrogens is known to be 0.399+/-0.004 and 0.426+/-0.004 Å from the mean porphyrin plane (ref. 5). The two EXAFS spectra are very similar, consistent with similar displacements of the irons. We find the same Fe-N distance of 2.06+/-0.01 Å in deoxyhaemoglobin as Eisenberger et al., but show that the displacement of the iron cannot be calculated from that distance.
- Publication:
-
Nature
- Pub Date:
- February 1982
- DOI:
- 10.1038/295535a0
- Bibcode:
- 1982Natur.295..535P