An Experimental and Quantum Chemical Investigation of CO Binding to Heme Proteins and Model Systems: A Unified Model Based on 13C, 17O, and 57Fe Nuclear Magnetic Reson
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- 作者：Michael T. McMahon ; Angel C. deDios ; Nathalie Godbout ; Renzo Salzmann ; David D. Laws ; Hongbiao Le ; Robert H. Havlin ; and Eric Oldfield
- 刊名：Journal of the American Chemical Society
- 出版年：1998
- 出版时间：May 20, 1998
- 年：1998
- 卷：120
- 期：19
- 页码：4784 - 4797
- 全文大小：218K
- 年卷期：v.120,no.19(May 20, 1998)
- ISSN：1520-5126
文摘
We have investigated the question of how CO ligands bind to ironin metalloporphyrins andmetalloproteins by using a combination of nuclear magnetic resonance(NMR), 57Fe Mössbauer, and infraredspectroscopic techniques, combined with density functional theoreticalcalculations to analyze the spectroscopicresults. The results of 13C NMR isotropic chemicalshift, 13C NMR chemical shift anisotropy, 17ONMRisotropic chemical shift, 17O nuclear quadrupole couplingconstant, 57Fe NMR isotropic chemical shift,57FeMössbauer quadrupolar splitting, and infrared measurementsindicate that CO binds to Fe in a close to linearfashion in all conformational substates. The13C-isotropic shift and shift anisotropy for anAo substate modelcompound:Fe(5,10,15,20-tetraphenylporphyrin)(CO)(N-methylimidazole),as well as the 17O chemical shift,and the 17O nuclear quadrupole coupling constant (NQCC) arevirtually the same as those found in the Aosubstate of Physeter catodon CO myoglobin and lead to mostprobable ligand tilt (
) and bend (
ddle">) angles of0
deg.gif"> and 1deg.gif"> when using a Bayesian probability or Z surfacemethod for structure determination. The infrared
CO for the model compound of 1969cm-1 is also that found for Aoproteins. Results for the A1 substate(including the 57Fe NMR chemical shift andMössbauer quadrupole splitting) are also consistent with closetolinear and untilted Fe-C-O geometries ( = 4deg.gif">, ddle"> = 7deg.gif">),with the small changes in ligand spectroscopicparameters being attributed to electrostatic field effects. Whentaken together, the 13C shift, 13C shiftanisotropy,17O shift, 17O NQCC, 57Feshift, 57Fe Mössbauer quadrupole splitting, andCO all strongly indicate very closeto linear and untilted Fe-C-O geometries for all carbonmonoxyhemeproteins. These results represent thefirst detailed quantum chemical analysis of metal-ligand geometriesin metalloproteins using up to sevendifferent spectroscopic observables from three types of spectroscopyand suggest a generalized approach tostructure determination.
) and bend (ddle">) angles of0deg.gif"> and 1deg.gif"> when using a Bayesian probability or Z surfacemethod for structure determination. The infraredCO for the model compound of 1969cm-1 is also that found for Aoproteins. Results for the A1 substate(including the 57Fe NMR chemical shift andMössbauer quadrupole splitting) are also consistent with closetolinear and untilted Fe-C-O geometries ( = 4deg.gif">, ddle"> = 7deg.gif">),with the small changes in ligand spectroscopicparameters being attributed to electrostatic field effects. Whentaken together, the 13C shift, 13C shiftanisotropy,17O shift, 17O NQCC, 57Feshift, 57Fe Mössbauer quadrupole splitting, andCO all strongly indicate very closeto linear and untilted Fe-C-O geometries for all carbonmonoxyhemeproteins. These results represent thefirst detailed quantum chemical analysis of metal-ligand geometriesin metalloproteins using up to sevendifferent spectroscopic observables from three types of spectroscopyand suggest a generalized approach tostructure determination.