9. Molybdenum and Tungsten Cofactors and the Reactions They Catalyze
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Martin L. Kirk
Abstract
The last 20 years have seen a dramatic increase in our mechanistic understanding of the reactions catalyzed by pyranopterin Mo and W enzymes. These enzymes possess a unique cofactor (Moco) that contains a novel ligand in bioinorganic chemistry, the pyranopterin ene-1,2-dithiolate. A synopsis of Moco biosynthesis and structure is presented, along with our current understanding of the role Moco plays in enzymatic catalysis. Oxygen atom transfer (OAT) reactivity is discussed in terms of breaking strong metal-oxo bonds and the mechanism of OAT catalyzed by enzymes of the sulfite oxidase (SO) family that possess dioxo Mo(VI) active sites. OAT reactivity is also discussed in members of the dimethyl sulfoxide (DMSO) reductase family, which possess des-oxo Mo(IV) sites. Finally, we reveal what is known about hydride transfer reactivity in xanthine oxidase (XO) family enzymes and the formate dehydrogenases. The formal hydride transfer reactivity catalyzed by xanthine oxidase family enzymes is complex and cleaves substrate C-H bonds using a mechanism that is distinct from monooxygenases. The chapter primarily highlights developments in the field that have occurred since ~2000, which have contributed to our collective structural and mechanistic understanding of the three canonical pyranopterin Mo enzymes families: XO, SO, and DMSO reductase.
Abstract
The last 20 years have seen a dramatic increase in our mechanistic understanding of the reactions catalyzed by pyranopterin Mo and W enzymes. These enzymes possess a unique cofactor (Moco) that contains a novel ligand in bioinorganic chemistry, the pyranopterin ene-1,2-dithiolate. A synopsis of Moco biosynthesis and structure is presented, along with our current understanding of the role Moco plays in enzymatic catalysis. Oxygen atom transfer (OAT) reactivity is discussed in terms of breaking strong metal-oxo bonds and the mechanism of OAT catalyzed by enzymes of the sulfite oxidase (SO) family that possess dioxo Mo(VI) active sites. OAT reactivity is also discussed in members of the dimethyl sulfoxide (DMSO) reductase family, which possess des-oxo Mo(IV) sites. Finally, we reveal what is known about hydride transfer reactivity in xanthine oxidase (XO) family enzymes and the formate dehydrogenases. The formal hydride transfer reactivity catalyzed by xanthine oxidase family enzymes is complex and cleaves substrate C-H bonds using a mechanism that is distinct from monooxygenases. The chapter primarily highlights developments in the field that have occurred since ~2000, which have contributed to our collective structural and mechanistic understanding of the three canonical pyranopterin Mo enzymes families: XO, SO, and DMSO reductase.
Kapitel in diesem Buch
- Frontmatter i
- About the Editors v
- Historical Development and Perspectives of the Series. Metal Ions in Life Sciences* vii
- Preface to Volume 20. Transition Metals and Sulfur: A Strong Relationship for Life ix
- Contents xiii
- Contributors to Volume 20 xix
- Titles of Volumes 1–44 in the Metal Ions in Biological Systems Series xxiii
- Contents of Volumes in the Metal Ions in Life Sciences Series xxv
- 1. Introduction: Transition Metals and Sulfur 1
- 2. Sulfur, the Versatile Non-metal 19
- 3. The Type 1 Blue Copper Site: From Electron Transfer to Biological Function 51
- 4. Purple Mixed-Valent Copper A 91
- 5. The Tetranuclear Copper-Sulfide Center of Nitrous Oxide Reductase 139
- 6. Cytochrome P450. The Dioxygen-Activating Heme Thiolate 165
- 7. Basic Iron-Sulfur Centers 199
- 8. The Cofactors of Nitrogenases 257
- 9. Molybdenum and Tungsten Cofactors and the Reactions They Catalyze 313
- 10. The Siroheme-[4Fe-4S] Coupled Center 343
- 11. Nickel, Iron, Sulfur Sites 381
- 12. Zinc Fingers 415
- SUBJECT INDEX 437
Kapitel in diesem Buch
- Frontmatter i
- About the Editors v
- Historical Development and Perspectives of the Series. Metal Ions in Life Sciences* vii
- Preface to Volume 20. Transition Metals and Sulfur: A Strong Relationship for Life ix
- Contents xiii
- Contributors to Volume 20 xix
- Titles of Volumes 1–44 in the Metal Ions in Biological Systems Series xxiii
- Contents of Volumes in the Metal Ions in Life Sciences Series xxv
- 1. Introduction: Transition Metals and Sulfur 1
- 2. Sulfur, the Versatile Non-metal 19
- 3. The Type 1 Blue Copper Site: From Electron Transfer to Biological Function 51
- 4. Purple Mixed-Valent Copper A 91
- 5. The Tetranuclear Copper-Sulfide Center of Nitrous Oxide Reductase 139
- 6. Cytochrome P450. The Dioxygen-Activating Heme Thiolate 165
- 7. Basic Iron-Sulfur Centers 199
- 8. The Cofactors of Nitrogenases 257
- 9. Molybdenum and Tungsten Cofactors and the Reactions They Catalyze 313
- 10. The Siroheme-[4Fe-4S] Coupled Center 343
- 11. Nickel, Iron, Sulfur Sites 381
- 12. Zinc Fingers 415
- SUBJECT INDEX 437
