Table 1. EXAFS simulation parameters of lyophilized HYDA1 proteinsa.
| N [per Fe ion]/R [Å]/2σ2 × 103 [Å2] | RF [%] | ||||||
|---|---|---|---|---|---|---|---|
| HYDA1: | Fe-C/O | Fe-S | Fe-Fe, [2FeH] | Fe-Fe, [4FeH] | Fe…O/N | ||
| [4FeH] | −O2 | – | 4/2.28/7 | – | 3/2.73/10 | – | 9.0 |
| +O2 | – | 4/2.28/7 | – | 3/2.73/10 | – | 12.2 | |
| [6FeH] | −O2 | 1/1.91/5# | 3.5/2.27/10 | 0.5/2.55/2# | 2/2.72/7 | 1/3.00/5# | 12.5 |
| +O2 | 1/1.87/5# 0.82*/1.86/5# | 3.5/2.26/9 3.65*/2.26/10& | 0.5/2.58/2# 0.5/2.57/2# | 2/2.71/10 1.87*/2.71/7& | 1/3.05/5# 1/3.07/5# | 14.4 14.7 | |
| +O2 +H2O | 3.07*/2.04/5# | 1.73*/2.29/10& | 0.05*/2.55/2# | 0.39*/2.71/7& | 0.34*/3.18/5# | 13.8 | |
aN, coordination number; R, interatomic distance; 2σ2, Debye-Waller parameter; RF, fit error sum calculated for reduced distances of 1–3 Å25. Data correspond to EXAFS spectra in Fig. 4b. Fit restraints: N-values were fixed to the given numbers in the fits representing the expected coordination numbers for the [4Fe4S] cluster in HYDA1[4FeH] or the approximate N-values for a complete H-cluster in HYDA1[6FeH]21,28, *except for N-values that were allowed to vary in the fits; &the same 2σ2-values were used for respective fits of spectra plus or minus O2; #2σ2 values that were fixed in the simulations. For [6FeH] +O2, the fit result for unrestricted N-values (*) emphasizes that the Fe-CO/N and Fe-S bonds and the Fe-Fe interactions in the H-cluster are fully preserved in the presence of O2.