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  • 标题:Infrared spectroscopy of photodissociated carboxymyoglobin at low temperatures
  • 本地全文:下载
  • 作者:J O Alben ; D Beece ; S F Bowne
  • 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:1982
  • 卷号:79
  • 期号:12
  • 页码:3744-3748
  • DOI:10.1073/pnas.79.12.3744
  • 语种:English
  • 出版社:The National Academy of Sciences of the United States of America
  • 摘要:We have studied the infrared spectra of the bound and photodissociated states of Mb-12CO and Mb-13CO from 5.2 to 300 K. The absorbance peaks seen between 1800 and 2200 cm-1 correspond to CO stretching vibrations. In the bound state of Mb-12CO, the known lines A0 at 1969, A1 at 1945, and A2 at 1927 cm-1, have center frequencies, widths, and absorbances that are independent of temperature between 5.2 and 160 K. Above 160 K, A2 gradually shifts to 1933 cm-1. The low-temperature photodissociated state (Mb) shows three lines (B0, B1, B2) at 2144, 2131, and 2119 cm-1 for 12CO. The absorbances of the three lines depend on temperature. B0 is tentatively assigned to free CO in the heme pocket and B1 and B2, to CO weakly bound to the heme or heme pocket wall. The data are consistent with a model in which photodissociation of MbCO leads to B1 and B2. B2 decays thermally to B1 above 13 K; rebinding to A occurs from B1. The barriers between B2 and B1 and between B1 and A are described by activation enthalpy spectra. Heme and the central metal atom in state Mb have near-infrared, EPR, and Mossbauer spectra that differ slightly from those of deoxyMb. The observation of essentially free CO in state B implies that the difference between Mb and deoxyMb is not due to an interaction of the flashed-off ligand with the protein but is caused by an incomplete relaxation of the protein structure at low temperatures.
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