1.2- Dithiolenes resonance Raman spectroscopy

To date only DMSO reductase from R. sphaeroides forma specialis denitrificans (71) (Section III.A.4) has been studied by resonance Raman spectroscopy (40). The oxidized and reduced forms of DMSO reductase show vibrations in the 335- to 385-cm region that shift upon enrichment of the enzyme with S and that have been assigned to Mo—S vibrations. The most prominent feature is the band at 350 cm in oxidized DMSO reductase, which shifts to 341 cm upon S enrichment. For the oxidized state of the enzyme (presumably Mo(VD) the 350-cm band has been assigned to a Mo—S(dithiolene) vibration... 

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. 

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