硫酸還原菌中，亞硫酸還原酶能夠催化將亞硫酸還原為硫分子的反應。先前的研究指出，自Desulfovibrio gigas 中純化所得的異化亞硫酸還原酶（Dissimilatory sulfite reductase, DSR），也就是desulfoviridin，存在三種形態： Dsr-I、Dsr-II、Dsr-III。Dsr-I為α2β2γ2的二分子聚合體（dimer）結構，含有八個四鐵四硫群([4Fe-4S] cluster)、兩個鞍形的西羅血紅素（siroheme）和兩個sirohydrochlorin。 Dsr-II中，與兩個西羅血紅素分別結合的兩個四鐵四硫群被三鐵四硫群取代。不具活性的Dsr-III中，西羅血紅素不帶有中心鐵原子，而且也是用三鐵四硫群與西羅血紅素結合。 三種形態的Dsr都與desulfoviridin有一樣的特徵吸收波長：391nm, 408nm, 586nm, 628 nm，然而各吸收峰的吸收強度不同，在586nm附近的吸收峰的位置也有些微差異。 此外，Dsr-III在433nm有額外的吸收峰。
為了提供一個與厭氧菌生長時相近的環境，我們在無氧箱中仔細純化了三種形態的Dsr，全程用到的溶液都經過了除氧手續。我們觀察到無氧下純化所得的色譜圖（chromatogram）和先前研究中有氧環境所得的有所不同。 在有氧研究中Dsr-I吸收峰最高、Dsr-III最低，與在無氧狀態下得到的結果則呈現相反。由於鐵硫群是三種Dsr形態的主要差異之一，我們用了電子順磁共振(Electron Paramagnetic Resonance)圖譜圖譜來確認無氧下三種形態鐵硫群的差異。EPR圖譜中，Dsr-I和Dsr-III相似，兩者都沒有siroheme的訊號，在鐵硫群訊號方面，則是顯示了接近四鐵四硫群的訊號。Dsr-II則完全沒有訊號。我們認為三種Dsr裡的siroheme可能都處於還原態，而不在EPR中呈現訊號。我們猜測Dsr中鐵硫群原本以四鐵四硫群形式存在，在有氧純化中部份轉換為三鐵四硫群，而產生先前研究中的結果。然而，由於圖譜雜訊過高，此猜測尚無法證實。在紫外－可見光光譜（Ultraviolet–visible spectrum）中，主要的三個吸收峰位置大致相同，但A280的吸收值有比例上的差異，586nm附近的吸收峰並不如先前結果中有三種型態相異的情形，而是都集中在581nm。另外Dsr-I在550nm和425nm的吸收值有微弱的升起。

Angove, Hayley C, Sun Jae Yoo, Barbara K Burgess, and Eckard Münck. 1997. “Mössbauer and EPR Evidence for an All-Ferrous Fe4S4 Cluster with S = 4 in the Fe Protein of Nitrogenase.” Journal of the American Chemical Society 119(37):8730–8731.
Barton, Larry L., and Francisco A. Tomei. 1995. “Sulfate-Reducing Bacteria.” P. 21 in Sulfate-Reducing Bacteria, edited by Larry L. Barton. Plenum Press, New york.
Beinert, H, R H Holm, and E Münck. 1997. “Iron-Sulfur Clusters: Nature’s Modular, Multipurpose Structures.” Science 277(5326):653–659.
Brook, Itzhak. 1984. “Anaerobic infections in childhood.” Review of Infectious Diseases 14(2):45–51.
Brown, Janet N., Michael Hewins, Joop H.M. Van Der Linden, and Roderick J. Lynch. 1981. “Solvent degassing and other factors affecting liquid chromatographic detector stability.” Journal of Chromatography A 204(198 1):115–122.
Chan, M. K, J Kim, and D. C Rees. 1993. “The nitrogenase FeMo-cofactor and P-cluster pair: 2.2 A resolution structures.” Science (New York, N.Y.) 260(5109):792–4.
Chen, K, G J Tilley, V Sridhar, G S Prasad, C D Stout, F a Armstrong, and B K Burgess. 1999. “Alteration of the reduction potential of the [4Fe-4S](2+/+) cluster of Azotobacter vinelandii ferredoxin I.” The Journal of biological chemistry 274(51):36479–87.
Crane, B. R., L. M. Siegel, and E. D. Getzoff. 1995. “Sulfite Reductase Structure at 1.6  : Evolution and Catalysis for Reduction of Inorganic Anions.” Science 270(5233):59–67.
Guigliarelli, B, and P Bertrand. 1985. “Interconversions between the 3Fe and 4Fe forms of the iron-sulfur clusters in the ferredoxin from Thermodesulfobacterium commune: EPR characterization and potentiometric titration.” Biochimica et Biophysica Acta (BBA) - Bioenergetics 810(3):319–324.
Howard, James B., and Douglas C. Rees. 1996. “Structural Basis of Biological Nitrogen Fixation.” Chemical reviews 96(7):2965–2982.
Hsieh, Yin-Cheng. 2010. “Structural insights into the enzyme catalysis from comparison of three forms of dissimilatory sulfite reductase from desulfovibrio gigas.” National Tsing Hua University.
Hsieh, Yin-Cheng, Ming-Yih Liu, Vincent C-C Wang, Yen-Lung Chiang, En-Huang Liu, Wen-guey Wu, Sunney I Chan, and Chun-Jung Chen. 2010. “Structural insights into the enzyme catalysis from comparison of three forms of dissimilatory sulphite reductase from Desulfovibrio gigas.” Molecular microbiology 78(5):1101–16.
Janick, P a, and L M Siegel. 1982. “Electron paramagnetic resonance and optical spectroscopic evidence for interaction between siroheme and Fe4S4 prosthetic groups in Escherichia coli sulfite reductase hemoprotein subunit.” Biochemistry 21(15):3538–47.
Kang, L, and J LeGall. 1987. “Spectroscopic properties of siroheme extracted from sulfite reductases.” Journal of Inorganic Biochemistry 30(4):273–290.
Klimmek, O. 2005. “The biological cycle of sulfur.” Metal ions in biological systems.
Moura, I, H D Peck, and D V Dervartanian. 1988. “Characterization of Two Dissimilatory Sulfite Reductases (Desulforubidin and Desulfoviridin) from the Sulfate-Reducing Bacteria. Mossbauer and EPR Studies.” (9):1075–1082.
Moura, Jose J G, Isabel Moura, Thomas A Kent, John D Lipscombl, Boi Hanh Huynhji, Jean Legall, Antonio V Xavier, Eckard Munck, J D Lipscomb, B H Huynh, and E Münck. 1982. “Interconversions of [3Fe-3S] and [4Fe-4S] clusters. Mössbauer and electron paramagnetic resonance studies of Desulfovibrio gigas ferredoxin II.” Journal of Biological Chemistry 257(11):6259–6267.
Murphy, MJ, and LM Siegel. 1973. “Siroheme and sirohydrochlorin. The basis for a new type of porphyrin-related prosthetic group common to both assimilatory and dissimilatory sulfite reductases.” The Journal of biological chemistry 248(19):6911–6919.
Peck Jr., H.D. 1961. “Enzymatic basis for assimilatory and dissimilatory sulfate reduction.” Journal of bacteriology.
Pilbrow, John R., and Graeme R. Hanson. 1993. “Electron Paramagnetic Resonance.” Pp. 330–353 in Methods in Enzymology V.227, edited by James F. Riordan and Bert L. Vallee.
Przysiecki, C T, T E Meyer, and M a Cusanovich. 1985. “Circular dichroism and redox properties of high redox potential ferredoxins.” Biochemistry 24(10):2542–9.
Seki, Y, K Kobayashi, and M. Ishimoto. 1979. “Biochemical studies on sulfate-reducing bacteria. XV. Separation and comparison of two forms of desulfoviridin.” Journal of biochemistry 85(3):705–711.
Sievert, SM. 2007. “The sulfur cycle.”
Stephens, P. J., D. R. Jollie, and a. Warshel. 1996. “Protein Control of Redox Potentials of Iron−Sulfur Proteins.” Chemical Reviews 96(7):2491–2514.
Thomson, Andrew J., A.Edward Robinson, Michael K. Johnson, Richard Cammack, K.Krishna Rao, and David O. Hall. 1981. “Low-temperature magnetic circular dichroism evidence for the conversion of four-iron-sulphur clusters in a ferredoxin from Clostridium pasteurianum into three-iron-sulphur clusters.” Biochimica et Biophysica Acta (BBA) - Bioenergetics 637(3):423–432.
Walden, W C, and D J Hentges. 1975. “Differential effects of oxygen and oxidation-reduction potential on the multiplication of three species of anaerobic intestinal bacteria.” Applied microbiology 30(5):781–5.
Wolfe, Bonnie M, Siu Man Lui, and James A Cowan. 1994. “Desulfoviridin , a multimeric-dissimilatory sulfite reductase from Desulfovibrio vulgaris ( Hildenborough ).” 89:79–89.