HiPIP ENDOR

Figure 15. Comparison of H-ENDOR spectra of the HiPIPs from E. hal. II (left panel) and E. hal. I and its variant F36G (right panel). Spectra were recorded at the field posititms indicated in EPR spectrum (left panel, top). The gray circles mark the interaction of HCB Phe48 in E. hal. II and correspondingly of HCB Phe36 in E.hal. I. This interaction vanishes in the F36G variant.

Figure 17. ENDOR spectra of Fe-enriched HiPIP of E. hal. II at three g-selections (a) g = 2.143, (b) g = 2.053, and (c) g = 2.030 (refer to EPR spectrum in Fig. 15). Two groups of Fc resonances are marked with arrows and are partly overlapping with proton lines (indicated by sticks).

ENDOR patterns as (basic) doublets separated by about 1 MHz and centered at about 16.5 MHz (mixed-valence) and 9.25 MHz (ferric pair). Therefore, as for the [2Fe2S] clusters, there should be considerable overlap with proton resonances when the measurements are taken at the usual X-band frequencies. Fortunately, the results for E. halophila II are shown in Figure 17 for three g-factors have better resolution than the ones discussed above for the [2Fe2S] clusters. Although there is no distinction possible between the individual irons within one tine group, the mixed-valence pair and the ferric pair are nicely distinguishable from the protons when the Fe sample is used for comparison (data not shown). Comparison with the available data based mostly on MSssbauer spectroscopy from several HiPIP... 

Dilg AWE, Capozzi F, Mentler M, Iakovleva O, Luchinat C, Bertini I, Parak FG. 2001. Comparison and characterization of the [Fe4S4] centre in the wild-type and C77S mutated HiPIPs from Chromatium vinosum monitored by Mdssbauer, Fe ENDOR and EPR spectroscopies. JBiol Inorg Chem 6 232-246. 

---