The bacterial sulfane dehydrogenase SoxCD is a distantly related member of the sulfite oxidase (SO) enzyme family that is proposed to oxidize protein-bound sulfide) (sulfane) of SoxY as part of a multienzyme mechanism of thiosulfate metabolism. This study characterized the molybdenum cofactor of SoxCD(1), comprising the catalytic molybdopterin subunit SoxC and the truncated c-type cytochrome subunit SoxD(1). Electron paramagnetic resonance spectroscopy of the Mo-v intermediate generated by dithionite reduction revealed low- and high-pH species with g and A(Mo-95.97) matrices nearly identical to those of SO, indicating a similar pentacoordinate active site in SoxCD(1). However, no sulfite-induced reduction to Mo-v was detected, nor could a strongly coupled H-1 signal or a phosphate-inhibited species be generated. This indicates that the outer coordination sphere controls substrate binding in SoxCD, permitting access only to protein-bound sulfur via the C-terminal tail of SoxY.