Fax +41 61 306 12 34 E-Mail karger@karger.ch www.karger.com Minireview J Mol Microbiol Biotechnol 2005;10:223–233 DOI: 10.1159/000091567 Key Bacterial Multi-Centered Metal Enzymes Involved in Nitrate and Sulfate Respiration G. Fritz a O. Einsle b M. Rudolf a A. Schiffer a P.M.H. Kroneck a a Fachbereich Biologie, Universität Konstanz, Konstanz, and b Institut für Mikrobiologie und Genetik, Abteilung Molekulare Strukturbiologie, Georg-August-Universität Göttingen, Göttingen, Germany Introduction The biogeochemical cycling of the basic elements of life including carbon, nitrogen, oxygen, and sulfur, has attracted the interest of many researchers over the past decades. Of similar importance, the biogeochemistry of the essential transition metals has been extensively stud- ied because of their functions as cofactors, or as part of cofactors in enzymes, and as structural elements in pro- teins. Note that metal proteins comprise one third to one half of known proteins. Many processes essential for life strictly depend on transition metal ions and their ability to catalyze multi-electron redox and hydrolytic transfor- mations. The essential transition metal ions for terres- trial organisms include vanadium to zinc of the first-row transition metal series and molybdenum and tungsten in the second- and third-row series [Kroneck, 2005; Schu- macher et al., 1997]. Basic elements, such as nitrogen or sulfur, can exist in the biosphere in several oxidation states, ranging from N(5+) in nitrate to N(3–) in ammonia, and S(6+) in sul- fate to S(2–) in hydrogen sulfide [Klimmek, 2005; Rudolf and Kroneck, 2005]. Interconversions of these various species constitute their biogeochemical cycles which are sustained by complex biological processes, with bacteria playing a prominent role. Specialized metal enzymes do- Key Words Adenosine-5  -phosphosulfate reductase  Cytochrome c nitrite reductase  Nitrate ammonification  Sulfite reductase  Sulfate respiration Abstract Many essential life processes, such as photosynthesis, respiration, nitrogen fixation, depend on transition met- al ions and their ability to catalyze multi-electron redox and hydrolytic transformations. Here we review some recent structural studies on three multi-site metal en- zymes involved in respiratory processes which represent important branches within the global cycles of nitrogen and sulfur: (i) the multi-heme enzyme cytochrome c ni- trite reductase, (ii) the FAD, FeS-enzyme adenosine-5  - phosphosulfate reductase, and (iii) the siroheme, FeS- enzyme sulfite reductase. Structural information comes from X-ray crystallography and spectroscopical tech- niques, in special cases catalytically competent interme- diates could be trapped and characterized by X-ray crys- tallography. Copyright © 2005 S. Karger AG, Basel Peter M.H. Kroneck Universität Konstanz, Mathematisch-Naturwissenschaftliche Sektion Fachbereich Biologie DE–78457 Konstanz (Germany) Tel. +49 7531 882 103, Fax +49 7531 882 966, E-Mail peter.kroneck@uni-konstanz.de © 2005 S. Karger AG, Basel 1464–1801/05/0104–0223$22.00/0 Accessible online at: www.karger.com/mmb Dedicated to Norbert Pfennig in honor of his 80th birthday.