文章基本信息

标题：Structure-function relations in hemoglobin as determined by x-ray absorption spectroscopy
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作者：P Eisenberger ; R G Shulman ; G S Brown 等
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1976
卷号：73
期号：2
页码：491-495
DOI：10.1073/pnas.73.2.491
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Conclusions concerning the structure around the iron atom in oxy- and carbonmonoxyhemoglobin have been obtained by fluorescent x-ray absorption studies. The bis-imidazole heme complex was used as a model system of known structure. The ligated forms of hemoglobin, and cytochrome c at high pH, gave spectra which were very similar to the bis-imidazole complex, where the average Fe-N bond distance is known to be 1.98 A. By comparison it was possible to determine that the average Fe-N bond distances were 1.99 A in oxyhemoglobin, 1.98 A in carbonmonoxyhemoglobin, and 1.98 A in cytochrome c at pH less than 10.5, with an experimental accuracy of +/-0.02 A. An experimental comparison between oxy- and deoxyhemoglobin A showed much larger spectral changes than amongst the ligated forms. A comparison was made between the low oxygen affinity form of deoxy HbA and the high affinity form of doexy Hb Kempsey (alpha2beta992 Asp leads to Asn). All the spectral features coincided, allowing us to conclude that the average iron-ligand bond differences must be less than or equal to 0.02 A. Since the strain energy is proportional to the square of this displacement, we show that the strain energy at the iron is less than or equal to 4 X 10(-3) eV. This is negligible compared to the difference of binding energy of the high and low affinity forms, which is 0.15 eV, showing that the energies responsible for the increase of oxygen affinity are not localized at the heme.