Pr chromophore undergoes a cis–trans isomerization between carbons 15 and 16 and rotation of the C14-C15 single bond on red light exposure.

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Nitrogenase is a complex consisting of the MoFe protein (dinitrogenase or component I) a heterotetramer, and the Fe protein (dinitrogenase reductase or component II) a homodimer.

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Fe protein 

contains 2 identical subunits (dimer) – nif H

Each subunit has MW of 30 ~ 72 kD.

Each subunit contains an Fe-S cluster (4Fe and 4S2-).

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MoFe protein 

2 pairs of identical subunits (tetramer, nif D & nif K)

A total of MW 180 ~ 235kD

Each subunit has 2 Mo-Fe-S clusters.

Both Fe proteins and MoFe proteins are sensitive to O2. 

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#Id: 9272

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#Id: 9273

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