Raman spectroscopy iron-sulfur cluster

Resonance Raman Spectroscopy of Iron—Oxo and Iron—Sulfur Clusters in Proteins... 

Valuable spectroscopic studies on the dithiolene chelated to Mo in various enzymes have been enhanced by the knowledge of the structure from X-ray diffraction. Plagued by interference of prosthetic groups—heme, flavin, iron-sulfur clusters—the majority of information has been gleaned from the DMSO reductase system. The spectroscopic tools of X-ray absorption spectroscopy (XAS), electronic ultraviolet/visible (UV/vis) spectroscopy, resonance Raman (RR), MCD, and various electron paramagnetic resonance techniques [EPR, electron spin echo envelope modulation (ESEEM), and electron nuclear double resonance (ENDOR)] have been particularly effective probes of the metal site. Of these, only MCD and RR have detected features attributable to the dithiolene unit. Selected results from a variety of studies are presented below, chosen because their focus is the Mo-dithiolene unit and organized according to method rather than to enzyme or type of active site. 

Indeed it may be that 3Fe clusters are always extruded as [2Fe-2S] clusters, an observation that would have structural implications. The use of resonance Raman and MCD spectroscopy " has allowed valuable distinctions to be made between these clusters, while ESR techniques seem to be of particular value. Thus, the first indication of a 3Fe cluster in an iron-sulfur protein has usually been the observation of a g = 2.01 signal in the ESR spectrum, but it should be noted that there may be confusion with oxidized HiPIP clusters. 

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