Biological nitrogen fixation is catalyzed by the enzyme nitrogenase, which facilitates the cleavage of the relatively inert triple bond of N₂. Nitrogenase is most commonly associated with the molybdenum–iron cofactor called FeMoco or the M-cluster, and it has been the subject of extensive structural and spectroscopic characterization over the past 60 years. In the late 1980s and early 1990s, two “alternative nitrogenase” systems were discovered, isolated, and found to incorporate V or Fe in place of Mo. These systems are regulated by separate gene clusters; however, there is a high degree of structural and functional similarity between each nitrogenase. Limited studies with the V- and Fe-nitrogenases initially demonstrated that these enzymes were analogously active as the Mo-nitrogenase, but more recent investigations have found capabilities that are unique to the alternative systems. In this review, we will discuss the reactivity, biosynthetic, and mechanistic proposals for the alternative nitrogenases as well as their electronic and structural properties in comparison to the well-characterized Mo-dependent system. Studies over the past 10 years have been particularly fruitful, though key aspects about V- and Fe-nitrogenases remain unexplored.

中文翻译：

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替代性固氮酶的反应性，机理和组装。

生物固氮是由固氮酶催化的，该酶促进了N ₂相对惰性三键的裂解。。氮酶最常与称为FeMoco的钼铁辅因子或M簇相关，在过去60年中，它一直是广泛的结构和光谱表征的主题。在1980年代末期和1990年代初，发现，分离了两个“替代的硝化酶”系统，并掺入了V或Fe来代替Mo。这些系统受单独的基因簇调控。但是，每个固氮酶之间在结构和功能上都有高度的相似性。对V-和Fe-氮酶的有限研究最初表明，这些酶的活性与Mo-氮酶类似，但是最近的研究发现，这种功能是替代系统所独有的。在这篇评论中，我们将讨论反应性，生物合成，以及与特征明确的Mo依赖系统相比的替代性Nase及其机械和电子特性的机械建议。尽管有关V-和Fe-氮酶的关键方面尚未探索，但过去10年的研究尤其富有成果。