Table 2.
Selected EXAFS fits to the NO-bound and Fe(II)–unligated states of Tt H-NOX.a
| Tt H-NOX Fe(II)–NO | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
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| fit 1 | fit 2 | fit 3 | fit 4 | ||||||||
| shell | r | σ 2 | shell | r | σ 2 | shell | r | σ 2 | shell | r | σ 2 |
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| 1 Fe-NO | 1.75 | 5.1 | 1 Fe-NO | 1.73 | 3.0 | 1 Fe-NO | 1.74 | 5.4 | |||
| 4 Fe-Np | 1.99 | 3.9 | 4 Fe-Np | 1.97 | 3.3 | 4 Fe-Np + 1 Fe- NHis |
1.97 | 5.1 | 4 Fe-Np | 1.97 | 3.4 |
| 1 Fe-NHis | 2.32 | 6.5 | |||||||||
| 8 Fe••Cα | 3.01 | 3.3 | 8 Fe••Cα | 2.99 | 3.6 | 8 Fe••Cα | 2.99 | 3.6 | 8 Fe••Cα | 2.99 | 3.5 |
| 16 Fe••Cα/Np | 3.18 | 6.8 | 16 Fe••Cα/Np | 3.16 | 7.2 | 16 Fe••Cα/Np | 3.16 | 7.2 | 16 Fe••Cα/Np | 3.16 | 7.1 |
| 4 Fe••Ch | 3.10 | 37.5 | 4 Fe••Ch | 3.34 | 4.9 | 4 Fe••Ch | 3.34 | 4.9 | 4 Fe••Ch | 3.35 | 4.5 |
| 8 Fe••Cβ | 4.36 | 6.3 | 8 Fe••Cβ | 4.31 | 5.5 | 8 Fe••Cβ | 4.31 | 5.4 | 8 Fe••Cβ | 4.31 | 5.5 |
| 16 Fe••Cβ/Np | 4.39 | 12.6 | 16 Fe••Cβ/Np | 4.34 | 11.0 | 16 Fe••Cβ/Np | 4.33 | 10.8 | 16 Fe••Cβ/Np | 4.33 | 11.0 |
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| F | 0.369 | F | 0.286 | F | 0.315 | F | 0.270 | ||||
| ΔE0 | 8.40 | ΔE0 | 3.76 | ΔE0 | 3.43 | ΔE0 | 3.48 | ||||
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| Tt H-NOX Fe(II)–unligated | |||||||||||
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| fit 5 | fit 6 | fit 7 | fit 8 | ||||||||
| shell | r | σ 2 | shell | r | σ 2 | shell | r | σ 2 | shell | r | σ 2 |
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| 4 Fe-Np | 2.02 | 7.2 | 4 Fe-Np + 1 Fe-NHis |
2.02 | 10.0 | 4 Fe-Np | 2.02 | 7.2 | 4 Fe-Np + 1 Fe-NHis |
2.03 | 10.3 |
| 1 Fe-NHis/O | 2.69 | 2.6 | 1 Fe-O | 2.38 | 3.2 | ||||||
| 8 Fe••Cα | 3.11 | 13.4 | 8 Fe••Cα | 3.12 | 15.9 | 8 Fe••Cα | 3.09 | 15.0 | 8 Fe••Cα | 3.12 | 14.2 |
| 4 Fe••Ch | 3.40 | −0.3 | 4 Fe••Ch | 3.40 | −0.4 | 4 Fe••Ch | 3.40 | −0.5 | 4 Fe••Ch | 3.40 | −0.8 |
| 8 Fe••Cβ | 4.39 | 3.7 | 8 Fe••Cβ | 4.39 | 4.0 | 8 Fe••Cβ | 4.39 | 3.8 | 8 Fe••Cβ | 4.39 | 3.3 |
| 16 Fe••Cβ/Np | 4.42 | 7.5 | 16 Fe••Cβ/Np | 4.42 | 8.0 | 16 Fe••Cβ/Np | 4.42 | 7.7 | 16 Fe••Cβ/Np | 4.42 | 6.7 |
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| F | 0.381 | F | 0.436 | F | 0.362 | F | 0.411 | ||||
| ΔE0 | 4.95 | ΔE0 | 4.94 | ΔE0 | 4.98 | ΔE0 | 4.98 | ||||
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r is in units of Å; σ2 is in units of 10−3 Å2; ΔE0 is in units of eV. All fits are to unfiltered data. F represents a goodness-of-fit parameter. Fourier transform ranges: k = 2.0 – 13.85 Å−1 (resolution = 0.134 Å) for Tt H-NOX Fe(II)–NO; k = 2.0 – 12.0 Å−1 (resolution = 0.157 Å) for Tt H-NOX Fe(II)–unligated. Values of r for the Fe••Cα single scattering and Fe••Cα/Np multiple scattering paths were constrained to a constant difference from one another, while σ2 for the multiple scattering path was constrained to be twice that of the single scattering path. A similar constraint was placed on the Cβ and Cβ/Np combination. Inclusion of the Fe••Cα/Np multiple scattering paths was not required for fits of Fe(II)-unligated data.