Key bacterial multi-centered metal enzymes involved in nitrate and sulfate respiration.

Many essential life processes, such as photosynthesis, respiration, nitrogen fixation, depend on transition metal ions and their ability to catalyze multi-electron redox and hydrolytic transformations. Here we review some recent structural studies on three multi-site metal enzymes involved in respiratory processes which represent important branches within the global cycles of nitrogen and sulfur: (i) the multi-heme enzyme cytochrome c nitrite 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 techniques, in special cases catalytically competent intermediates could be trapped and characterized by X-ray crystallography. Copyright 2005 S. Karger AG, Basel.