Cleaving the N,N Triple Bond: The Transformation of Dinitrogen to Ammonia by Nitrogenases - The Metal-Driven Biogeochemistry of Gaseous Compounds in the Environment - page 143

Chapter 7
Cleaving the N,N Triple Bond:
The Transformation of Dinitrogen
to Ammonia by Nitrogenases

Chi Chung Lee, Markus W. Ribbe, and Yilin Hu

Contents
ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148

1 INTRODUCTION ......................................................................... 148

2 THE STRUCTURAL AND BIOCHEMICAL PROPERTIES
OF Mo-NITROGENASE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150

2.1 The Fe Protein and Its Associated Metal Clusters ................................. 151

2.1.1 The Polypeptide . . . . . . . . . . . . . ................................................ 151

2.1.2 The [Fe 4 S 4 ] Cluster . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152

2.2 The MoFe Protein and Its Associated Metal Clusters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154

2.2.1 The Polypeptide . . . . . . . . . . . . . ................................................ 154

2.2.2 The P-cluster . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156

2.2.3 The FeMoco . . . . ............................................................. 156

3 THE CATALYTIC MECHANISM OF Mo-NITROGENASE . . . . . . . . . . . . . . . . . . . . . . . . . . 157

3.1 The Thorneley-Lowe Model . ...................................................... 158

3.1.1 The Fe Protein Cycle ....................................................... 158

3.1.2 The MoFe Protein Cycle . . .................................................. 160

3.2 Further Development and Modifications of the Thorneley-Lowe Model ......... 162

3.2.1 Intermediates of the MoFe Protein Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162

3.2.2 The Reductive Dihydrogen Elimination Mechanism ...................... 164

3.2.3 The Alternating Dinitrogen Reduction Pathway . . . . . . . . . . . . . . . . . . . . . . . . . . . 165