Müller A, Schneider K, Knüttel K, Hagen WR. EPR spectroscopic characterization of an 'iron only' nitrogenase. S = 3/2 spectrum of component 1 isolated from Rhodobacter capsulatus.
FEBS Lett 1992;
303:36-40. [PMID:
1317300 DOI:
10.1016/0014-5793(92)80472-s]
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Abstract
The alternative nitrogenase of Rhodobacter capsulatus, isolated from a nifHDK deletion mutant, has been purified to near homogeneity and identified as an 'iron only' nitrogenase. The dithionite-reduced component 1 ('FeFe protein') of this enzyme showed an EPR spectrum consisting of two components: a minor S = 1/2 signal at g = 1.93 and a very characteristic S = 3/2 signal of near-stoichiometric intensity at g = 5.44. This resonance is very close to the highest possible g value (g = 5.46) for the coinciding two intradoublet subspectra of an S = 3/2 system of maximal rhombicity (E/D = 0.33). The deviation from axial symmetry (increasing E/D) correlates with the stability, activity and substrate selectivity of the different (Mo, V, Fe) nitrogenases.
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