Characterization of two dissimilatory sulfite reductases (desulforubidin and desulfoviridin) from the sulfate-reducing bacteria. Moessbauer and EPR studies

In this paper, the authors report a detailed Moessbauer investigation of two different sulfite reductases, namely, desulforubidin from D. baculatus and desulfoviridin from D. gigas. In order to better characterize the prosthetic groups, they have also studied the EPR spectra and determined the iron and heme contents of the /sup 57/Fe-enriched enzymes. They found that desulforubidin contains exchange-coupled siroheme-(4Fe-4S) units which are similar to those found in the hemoprotein subunit of E. coli sulfite reductase. To their surprise, they discovered that the majority of the purified desulfoviridin contains demetalized sirohydrochlorin, with only a minor portion of the sample containing siroheme. The siroheme in desulfoviridin was also found to be coupled with a (4Fe-4S) cluster.