Copper proteins ENDOR studies

In frozen solution EPR spectra of copper proteins, ligand and copper hf interactions are only partially resolved, or not at all. It is therefore striking that only few ENDOR studies on copper proteins have been published so far17,199-201). Nevertheless, these few ENDOR results already demonstrate the power of the double resonance technique to probe the coordination environment of the copper-containing sites in these types of proteins. 

In ENDOR studies, maximum spectroscopic information is obtained, if the paramagnetic compounds are diluted into diamagnetic single crystal hosts. However, it is often not possible to find suitable host compounds or to grow sufficiently large crystals. This is particularly true with biological systems, e.g. copper or iron proteins. Crystalline powders or frozen solution samples, on the other hand, can normally be prepared more easily. For such randomly oriented compounds, Rist and Hyde have shown that... 

In other systems, W-band EPR and X-band Fe-ENDOR have been used to characterize a new stable diiron centre found in the E. coli RNR mutant R2-Y122H. The spectrum was fully resolved at 94 GHz and evidence was given to support the view that the centre was a Fe Fe " centre with a strongly coupled radical. Pulsed EPR at 95 GHz has been used to characterize the azurin mutant M121H, a blue copper protein, in a single-crystal study which allowed the complete g tensor to be determined relative to the molecular axes. ... 

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