On the Formation of an Oxygen-Tolerant Three Component Nitrogenase Complex from Azotobacter Vinelandii

Scherings, G.; Haaker, H.; Wassink, Johannes H.

doi:10.1007/978-94-009-6923-0_103

Cited by 2 publications

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“…Its role is to supply electrons to the cysteine desulfurase IscS aiding in the reduction of S 0 to S − 2 [27]. The Shethna protein is part of the so‐called nitrogenase conformational protection mechanism as it has been shown to associate with nitrogenase under conditions of O 2 stress and protect it from oxidative damage [28]. The roles of many other A. vinelandii ferredoxins remain unassigned.…”

Section: Discussionmentioning

confidence: 99%

Role of Azotobacter vinelandii FdxN in FeMo‐co biosynthesis

et al. 2013

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a b s t r a c tBiosynthesis of metal clusters for the nitrogenase component proteins NifH and NifDK involves electron donation events. Yet, electron donors specific to the biosynthetic pathways of the [4Fe-4S] cluster of NifH, or the P-cluster and the FeMo-co of NifDK, have not been identified. Here we show that an Azotobacter vinelandii mutant lacking fdxN was specifically impaired in FeMo-co biosynthesis. The DfdxN mutant produced 5-fold less NifB-co, an early FeMo-co biosynthetic intermediate, than wild type. As a consequence, it accumulated FeMo-co-deficient apo-NifDK and was impaired in Nif-DK activity. We conclude that FdxN plays a role in FeMo-co biosynthesis, presumably by donating electrons to support NifB-co synthesis by NifB. This is the first role in nitrogenase biosynthesis unequivocally assigned to any A. vinelandii ferredoxin.

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Section: Discussionmentioning

confidence: 99%

Role of Azotobacter vinelandii FdxN in FeMo‐co biosynthesis

et al. 2013

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“…Investigations of the mechanism underlying the switch‐off reaction revealed an association of the nitrogenase complex with a low‐molecular‐mass FeSII protein. Formation of the three‐component complex depends on the oxidation of nitrogenase and of its electron donor [11,12]. Studies on the physiological significance of the FeSII protein revealed that a mutant of A. vinelandii devoid of the FeSII protein was not impaired in its ability to grow diazotrophically in the presence of O 2 [13].…”

Section: Control Of Nitrogen Fixationmentioning

confidence: 99%

“…During the past 30 years, more detailed information has become available on the mechanism and the physiological significance of conformational protection of nitrogenase [11–13]. But as yet, there is no direct experimental evidence proving that the cytoplasm is kept anoxic by cellular respiration.…”

Section: Introductionmentioning

confidence: 99%

Respiratory protection of nitrogenase inAzotobacterspecies: is a widely held hypothesis unequivocally supported by experimental evidence?

Oelze

2000

FEMS Microbiol Rev

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The hypothesis of respiratory protection, originally formulated on the basis of results obtained with Azotobacter species, postulates that consumption of O(2) at the surface of diazotrophic prokaryotes protects nitrogenase from inactivation by O(2). Accordingly, it is assumed that, at increased ambient O(2) concentrations, nitrogenase activity depends on increased activities of a largely uncoupled respiratory electron transport system. The present review compiles evidence indicating that cellular O(2) consumption as well as both the activity and the formation of the respiratory system of Azotobacter vinelandii are controlled by the C/N ratio, that is to say the ratio at which the organism consumes the substrate (i.e. the source of carbon, reducing equivalents and ATP) per source of compound nitrogen. The maximal respiratory capacity which can be attained at increased C/N ratios, however, is controlled, within limits, by the ambient O(2) concentration. When growth becomes N-limited at increased C/N ratios, cells synthesize nitrogenase and fix N(2). Under these diazotrophic conditions, cellular O(2) consumption remains constant at a level controlled by the O(2) concentration. Control by O(2) has been studied on the basis of both whole cell respiration and defined segments of the respiratory electron transport chain. The results demonstrate that the effect of O(2) on the respiratory system is restricted to the lower range of O(2) concentrations up to about 70 microM. Nevertheless, azotobacters are able to grow diazotrophically at dissolved O(2) concentrations of up to about 230 microM indicating that respiratory protection is not warranted at increased ambient O(2) concentrations. This conclusion is supported and extended by a number of results largely excluding an obvious relationship between nitrogenase activity and the actual rate of cellular O(2) consumption. On the basis of theoretical calculations, it is assumed that the rate of O(2) diffusion into the cells is not significantly affected by respiration. All of these results lead to the conclusion that, in the protection of nitrogenase from O(2) damage, O(2) consumption at the cell surface is less effective than generally assumed. It is proposed that alternative factors like the supply of ATP and reducing equivalents are more important.

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On the Formation of an Oxygen-Tolerant Three Component Nitrogenase Complex from Azotobacter Vinelandii

Cited by 2 publications

References 0 publications

Role of Azotobacter vinelandii FdxN in FeMo‐co biosynthesis

Role of Azotobacter vinelandii FdxN in FeMo‐co biosynthesis

Respiratory protection of nitrogenase inAzotobacterspecies: is a widely held hypothesis unequivocally supported by experimental evidence?

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