Abstract
ABSTRACT The requirements for ATP and reductant during diazotrophic growth, the physicochemical properties of the nitrogenase proteins, and the involvement of Mo in different aspects of N2 fixation are reviewed. Irrespective of the source from which it is isolated, nitrogenase has very similar properties and is comprised of two O2-sensitive redox proteins. The Mo—Fe protein is an α2β2 tetramer of MW 220000, containing 2 Mo and approx. 33 ± 3 Fe and acid-labile S atoms per tetramer. The Mo atoms and approx. 40% of the Fe atoms can be extracted with N-methylformamide as a unique cofactor (FeMoco) which contains Mo, Fe and S2- in the ratios 1:8:4. Cluster extrusion and Mossbauer data are consistent with the presence of four 4Fe4S clusters in addition to two FeMoco clusters. The binding of substrate (C2H2), its reduction product C2H4, and the inhibitor CO to the Mo-Fe protein have been investigated by EPR spectroscopy. The Fe protein is γ2 dimer of MW 67000; spectroscopic and extrusion data indicate the prese...
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