Both the reductase and nitrogenase components of the complex are iron-sulfer proteins, in which iron is bonded to the sulfer atom of a cysteine residue and to inorganic.
The reductase (also called the iron protein or Fe protein), a dimer of identical 30-kd subunits, contains a [4Fe-4S] cluster.
An ATP/ADP binding site is also present at the subunit interface.
The role of the reductase is to transfer electrons from a high-potential donor, such as reduced ferredoxin, to the nitrogenase component.
Hydrolysis of ATP triggers electron transfer to the nitrogenase component and leads to the dissociation of the complex.
The reductase has the shape of a butterfly, with the ATP/ADP site located at the head.
The fluttering of its wings plays and essential role in electron transfer.
The nitrogenase component, an α2β2 tetramer (240 kd), also has a provocative structure.
Electrons enter at the P-cluster, which is located at an αβ interface.
Two [4Fe-4S] cubes are joined by sulfer atoms, which are in turn linked to cysteine residues.
Electrons flow from the P-cluster to the FeMo-cofactor, a very unusual redox center.
Because molybdenum is present in this cluster, the nitrogenase component is also called the molybdenum-iron protein. (MoFe protein)
The FeMo cofactor consists of two [M-3Fe-3S] clusters that are joined by three sulfer atoms.
Molybdenum occupies the M site in one cluster, and iron in the other.
The FeMo-cofactor is the site of nitrogen fixation.
It seems likely that N2 binds in the central cavity of this cofactor.
The formation of multiple Fe-N interactions in this complex weakens the nitrogen bond and thereby lowers the activation barrier for reduction.
Both the reductase and nitrogenase components of the complex are iron-sulfer proteins, in which iron is bonded to the sulfer atom of a cysteine residue and to inorganic.The reductase (also called the iron protein or Fe protein), a dimer of identical 30-kd subunits, contains a [4Fe-4S] cluster. An ATP/ADP binding site is also present at the subunit interface.The role of the reductase is to transfer electrons from a high-potential donor, such as reduced ferredoxin, to the nitrogenase component.Hydrolysis of ATP triggers electron transfer to the nitrogenase component and leads to the dissociation of the complex.The reductase has the shape of a butterfly, with the ATP/ADP site located at the head.The fluttering of its wings plays and essential role in electron transfer.The nitrogenase component, an α2β2 tetramer (240 kd), also has a provocative structure. Electrons enter at the P-cluster, which is located at an αβ interface.Two [4Fe-4S] cubes are joined by sulfer atoms, which are in turn linked to cysteine residues. Electrons flow from the P-cluster to the FeMo-cofactor, a very unusual redox center.Because molybdenum is present in this cluster, the nitrogenase component is also called the molybdenum-iron protein. (MoFe protein)The FeMo cofactor consists of two [M-3Fe-3S] clusters that are joined by three sulfer atoms. Molybdenum occupies the M site in one cluster, and iron in the other.The FeMo-cofactor is the site of nitrogen fixation.It seems likely that N2 binds in the central cavity of this cofactor. The formation of multiple Fe-N interactions in this complex weakens the nitrogen bond and thereby lowers the activation barrier for reduction.
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