Unification of reaction pathway and kinetic scheme for N
            <sub>2</sub>
            reduction catalyzed by nitrogenase

Lukoyanov, Dmitriy; Yang, Zhi Yong; Barney, Brett M.; Dean, Dennis R.; Seefeldt, Lance C.; Hoffman, Brian M.

doi:10.1073/pnas.1202197109

Cited by 58 publications

(123 citation statements)

References 26 publications

Supporting

Mentioning

114

Contrasting

Unclassified

Order By: Relevance

“…This signal was later determined to arise from an integer-spin system (where S ! 2, with a ground-state non-Kramers doublet) [75], which is consistent with the prediction that the odd-number states of the MoFe protein cycle (i.e., M n states where n is an odd number) are likely to be non-Kramer systems [57,76].…”

Section: Further Development and Modifications Of The Thorneley-lowe supporting

confidence: 82%

“…This plausible intermediate structure, depicted in Figure 5, also forms the basis for the hypothesis that N 2 may be reduced through a reductive elimination mechanism (see Section 3.2.3 for details). [74,75]. The M 7 state intermediate, designated H at the time of discovery, showed a broad EPR signal at low field in the Q-band EPR spectra.…”

Section: Further Development and Modifications Of The Thorneley-lowe mentioning

confidence: 98%

See 1 more Smart Citation

Cleaving the N,N Triple Bond: The Transformation of Dinitrogen to Ammonia by Nitrogenases

Lee

Ribbe

2014

The Metal-Driven Biogeochemistry of Gaseous Compounds in the Environment

View full text Add to dashboard Cite

Biological nitrogen fixation is a natural process that converts atmospheric nitrogen (N2) to bioavailable ammonia (NH3). This reaction not only plays a key role in supplying bio-accessible nitrogen to all life forms on Earth, but also embodies the powerful chemistry of cleaving the inert N,N triple bond under ambient conditions. The group of enzymes that carry out this reaction are called nitrogenases and typically consist of two redox active protein components, each containing metal cluster(s) that are crucial for catalysis. In the past decade, a number of crystal structures, including several at high resolutions, have been solved. However, the catalytic mechanism of nitrogenase, namely, how the N,N triple bond is cleaved by this enzyme under ambient conditions, has remained elusive. Nevertheless, recent biochemical and spectroscopic studies have led to a better understanding of the potential intermediates of N2 reduction by the molybdenum (Mo)-nitrogenase. In addition, it has been demonstrated that carbon monoxide (CO), which was thought to be an inhibitor of N2 reduction, could also be reduced by the vanadium (V)-nitrogenase to small alkanes and alkenes. This chapter will begin with an introduction to biological nitrogen fixation and Mo-nitrogenase, continue with a discussion of the catalytic mechanism of N2 reduction by Mo-nitrogenase, and conclude with a survey of the current knowledge of N2- and CO-reduction by V-nitrogenase and how V-nitrogenase compares to its Mo-counterpart in these catalytic activities.

show abstract

Section: Further Development and Modifications Of The Thorneley-lowe supporting

confidence: 82%

Section: Further Development and Modifications Of The Thorneley-lowe mentioning

confidence: 98%

Cleaving the N,N Triple Bond: The Transformation of Dinitrogen to Ammonia by Nitrogenases

Lee

Ribbe

2014

The Metal-Driven Biogeochemistry of Gaseous Compounds in the Environment

View full text Add to dashboard Cite

show abstract

“…30 Such featureless spectra cannot be used to correlate the intermediates reported here for NO 2 – and hydroxylamine turnover with H .…”

Section: Resultsmentioning

confidence: 97%

“…Thus, both the “N–N” nitrogenous substrates and the “N–O” substrates, NO 2 – and NH 2 OH, give rise to I , assigned as the E 8 state with NH 3 bound to FeMo-co. 7,4,29,30 …”

Section: Resultsmentioning

confidence: 99%

Nitrite and Hydroxylamine as Nitrogenase Substrates: Mechanistic Implications for the Pathway of N₂Reduction

et al. 2014

Self Cite

View full text Add to dashboard Cite

Investigations of reduction of nitrite (NO2–) to ammonia (NH3) by nitrogenase indicate a limiting stoichiometry, NO2– + 6e– + 12ATP + 7H+ → NH3 + 2H2O + 12ADP + 12Pi. Two intermediates freeze-trapped during NO2– turnover by nitrogenase variants and investigated by Q-band ENDOR/ESEEM are identical to states, denoted H and I, formed on the pathway of N2 reduction. The proposed NO2– reduction intermediate hydroxylamine (NH2OH) is a nitrogenase substrate for which the H and I reduction intermediates also can be trapped. Viewing N2 and NO2– reductions in light of their common reduction intermediates and of NO2– reduction by multiheme cytochrome c nitrite reductase (ccNIR) leads us to propose that NO2– reduction by nitrogenase begins with the generation of NO2H bound to a state in which the active-site FeMo-co (M) has accumulated two [e–/H+] (E2), stored as a (bridging) hydride and proton. Proton transfer to NO2H and H2O loss leaves M–[NO+]; transfer of the E2 hydride to the [NO+] directly to form HNO bound to FeMo-co is one of two alternative means for avoiding formation of a terminal M–[NO] thermodynamic “sink”. The N2 and NO2– reduction pathways converge upon reduction of NH2NH2 and NH2OH bound states to form state H with [−NH2] bound to M. Final reduction converts H to I, with NH3 bound to M. The results presented here, combined with the parallels with ccNIR, support a N2 fixation mechanism in which liberation of the first NH3 occurs upon delivery of five [e–/H+] to N2, but a total of seven [e–/H+] to FeMo-co when obligate H2 evolution is considered, and not earlier in the reduction process.

show abstract

“…Several recent studies have added to earlier work in building a probable mechanism for how N 2 might be reduced at the active site FeMo cofactor. One important insight relevant to the current discussion is the observation of metal-bound hydrides (determined as two hydrides bridging between Fe atoms) as an integral part of the FeMo-cofactor reactivity toward N 2 (43)(44)(45). These metal bound hydrides (M-H − ) have been proposed to participate in the initial reduction of N 2 to the proposed intermediate diazene (HN = NH).…”

Section: Discussionmentioning

confidence: 99%

Carbon dioxide reduction to methane and coupling with acetylene to form propylene catalyzed by remodeled nitrogenase

Yang

Moure

Dean

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

105

View full text Add to dashboard Cite

A doubly substituted form of the nitrogenase MoFe protein (α-70 Val→Ala , α-195 His→Gln ) has the capacity to catalyze the reduction of carbon dioxide (CO 2 ) to yield methane (CH 4 ). Under optimized conditions, 1 nmol of the substituted MoFe protein catalyzes the formation of 21 nmol of CH 4 within 20 min. The catalytic rate depends on the partial pressure of CO 2 (or concentration of HCO 3 − ) and the electron flux through nitrogenase. The doubly substituted MoFe protein also has the capacity to catalyze the unprecedented formation of propylene (H 2 C = CH-CH 3 ) through the reductive coupling of CO 2 and acetylene (HC≡CH). In light of these observations, we suggest that an emerging understanding of the mechanistic features of nitrogenase could be relevant to the design of synthetic catalysts for CO 2 sequestration and formation of olefins.is an abundant and stable form of carbon that is the product of respiration and burning of fossil fuels. As a result of these activities, the atmospheric concentration of CO 2 , a greenhouse gas, has been rising over the last century and contributing to global warming (1). There is strong interest in developing methods for sequestering CO 2 either by capturing it or by chemically converting it to valuable chemicals (2-5). Of particular interest are possible routes to reduction of CO 2 by multiple electrons to yield methanol (CH 3 OH) and methane (CH 4 ), which are renewable fuels (2). The reduction of CO 2 is difficult, with a limited number of reports of metal-based compounds able to catalyze these reactions (6-13). In biology, only a few enzymes are known to reduce CO 2 (14-18), and none of these can catalyze the eight electron reduction to CH 4 .The bacterial Mo-dependent nitrogenase enzyme catalyzes the multielectron/proton reduction of dinitrogen (N 2 ) to two ammonia (NH 3 ) at a metal cluster designated FeMo-cofactor [7Fe-9S-1Mo-1C-R-homocitrate] (Fig. 1) in a reaction that requires ATP hydrolysis and evolution of H 2 , with a minimal reaction stoichiometry shown in Eq. 1 (19)(20)(21)(22).Given that nitrogenase is effective at catalyzing the difficult multielectron reduction of N 2 , it was of interest to determine whether this enzyme might also catalyze the reduction of CO 2 to the level of CH 4 . Nitrogenase is known to have the capacity to reduce a variety of other small, relatively inert, doubly or triply bonded compounds, such as acetylene (HC≡CH) (19,23). It has been shown that an alternative form of nitrogenase, which contains V in place of Mo in the active site cofactor, has the remarkable capacity to reduce CO and couple multiple CO molecules, yielding short chain alkenes and alkanes such as ethylene (C 2 H 4 ), ethane (C 2 H 6 ), propylene (C 3 H 6 ), and propane (C 3 H 8 ) (24,25). In contrast, the Mo-nitrogenase is only able to reduce CO at exceedingly low rates (24). However, we have found that the MoFe protein can be remodeled by substitution of amino acid residues that provide the first shell of noncovalent interactions with the active site FeMo cofa...

show abstract

Unification of reaction pathway and kinetic scheme for N ₂ reduction catalyzed by nitrogenase

Cited by 58 publications

References 26 publications

Cleaving the N,N Triple Bond: The Transformation of Dinitrogen to Ammonia by Nitrogenases

Cleaving the N,N Triple Bond: The Transformation of Dinitrogen to Ammonia by Nitrogenases

Nitrite and Hydroxylamine as Nitrogenase Substrates: Mechanistic Implications for the Pathway of N₂Reduction

Carbon dioxide reduction to methane and coupling with acetylene to form propylene catalyzed by remodeled nitrogenase

Contact Info

Product

Resources

About

Unification of reaction pathway and kinetic scheme for N 2 reduction catalyzed by nitrogenase

Cited by 58 publications

References 26 publications

Cleaving the N,N Triple Bond: The Transformation of Dinitrogen to Ammonia by Nitrogenases

Cleaving the N,N Triple Bond: The Transformation of Dinitrogen to Ammonia by Nitrogenases

Nitrite and Hydroxylamine as Nitrogenase Substrates: Mechanistic Implications for the Pathway of N2Reduction

Carbon dioxide reduction to methane and coupling with acetylene to form propylene catalyzed by remodeled nitrogenase

Contact Info

Product

Resources

About

Unification of reaction pathway and kinetic scheme for N ₂ reduction catalyzed by nitrogenase

Nitrite and Hydroxylamine as Nitrogenase Substrates: Mechanistic Implications for the Pathway of N₂Reduction