Measurements in Heme Proteins

In the previous sections, we focused on the heme pocket of the heme proteins, whereby the intrinsic paramagnetic centers were used as the probes for structural information. However, the introduction of site-directed spin labeling has revolutionized the world of EPR in the sense that now also intrinsic diamagnetic proteins can be studied by EPR [77,78]. Indeed, in site-directed labeling, a paramagnetic spin label is attached to the protein through reaction of its functional group with the 

Eaton and their coworkers showed in an extensive series of experiments the possibilities of determining spin label to iron distances in spin-labeled ferric heme proteins using a series of cw-EPR, ESE, and saturation recovery (SR) experiments [80-86]. They clearly elucidate how die experimental results and their interpretation are affected by the spin state of die heme iron. These studies are nicely reviewed in [85]. 

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