Conformational substates of the Fe2+-His F8 linkage in deoxymyoglobin and hemoglobin probed in parallel by the Raman band of the Fe-His stretching vibration and the near-infrared absorption band III
✍ Scribed by H. Gilch; R. Schweitzer-Stenner; W. Dreybrodt; M. Leone; A. Cupane; L. Cordone
- Publisher
- John Wiley and Sons
- Year
- 1996
- Tongue
- English
- Weight
- 859 KB
- Volume
- 59
- Category
- Article
- ISSN
- 0020-7608
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✦ Synopsis
We measured the Y ~~-~, ~
Raman band of horse heart deoxymyoglobin and human deoxyhemoglobin as a function of temperature between 10 and 300 K. A self-consistent spectral analysis of the deoxymyoglobin Raman band reveals that it is underlied by three different sublines with frequencies at f l , = 209 cm-', i12 = 217 cm-', and R, = 225 cm-' and an identical half-width of 13 cm-l. All these parameters were found to be independent of temperature. These sublines were attributed to different conformational substates of the Fe2+-His F8 linkage, which comprise different out-off-plane displacements of the heme iron and tilt angles of the Fe2+-N,(His F8) bond. The intensity ratio 1J12 exhibits a van't Hoff behavior between 150 and 300 K, bends over in a region between 150 and 80 K, and remains constant at lower temperature. In contrast, I2/I1 shows a maximum at 170 K and approaches a constant value at 80 K. These data can be fitted by a modified van't Hoff expression, which accounts for the freezing into nonequilibrium distributions of substrates in a temperature interval AT around a distinct temperature TI and also for the linear temperature dependence of the protein's specific heat. The fits to the above intensity ratios yield a freezing temperature of TI = 117 K and a transition region of AT = 55 K. The v
~~-~~~
Raman band of human deoxyhemoglobin was decomposed into seven sublines with frequencies at 195,202,211,218,226,234, and 240 cm-', with half-widths of 12 cm-'. While the low-frequency sublines are strong at