Fig. 3.

Correlation between hinge angle (bars) and the distance between centroids (filled triangles) of the [4Fe:4S] and P cluster of the nitrogenase proteins in a series of states ordered along a potential reaction coordination for nucleotide hydrolysis. (Inset) The hinge angle is defined by the rotation angle about an axis along the dimer interface required to superimpose one subunit of a specified Fe-protein structure onto a subunit of the ADP-AlF₄⁻-stabilized Fe protein, after initially superimposing the other subunits in these structures.