Nitrogenase

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Nitrogenase
Nitrogenase.png
Identifiers
EC no. 1.18.6.1
CAS no. 9013-04-1
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IntEnz IntEnz view
BRENDA BRENDA entry
ExPASy NiceZyme view
KEGG KEGG entry
MetaCyc metabolic pathway
PRIAM profile
PDB structures RCSB PDB PDBe PDBsum
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NCBI proteins
Nitrogenase-type Oxidoreductase (component 1 subunit alpha/beta)
Identifiers
SymbolOxidored_nitro
Pfam PF00148
InterPro IPR000510
SCOP2 1mio / SCOPe / SUPFAM
Available protein structures:
Pfam   structures / ECOD  
PDB RCSB PDB; PDBe; PDBj
PDBsum structure summary
Nitrogenase iron protein NifH (component 2)
Identifiers
SymbolNifH
InterPro IPR005977
CATH 1fp6
SCOP2 d1fp6a_ / SCOPe / SUPFAM
CDD cd02040
Alternative nitrogenase (component 1) delta subunit
Identifiers
SymbolAnfG_VnfG
Pfam PF03139
InterPro IPR004349
Available protein structures:
Pfam   structures / ECOD  
PDB RCSB PDB; PDBe; PDBj
PDBsum structure summary

Nitrogenases are enzymes (EC 1.18.6.1 EC 1.19.6.1) that are produced by certain bacteria, such as cyanobacteria (blue-green bacteria) and rhizobacteria. These enzymes are responsible for the reduction of nitrogen (N2) to ammonia (NH3). Nitrogenases are the only family of enzymes known to catalyze this reaction, which is a step in the process of nitrogen fixation. Nitrogen fixation is required for all forms of life, with nitrogen being essential for the biosynthesis of molecules (nucleotides, amino acids) that create plants, animals and other organisms. They are encoded by the Nif genes or homologs. They are related to protochlorophyllide reductase.

Contents

Classification and structure

Although the equilibrium formation of ammonia from molecular hydrogen and nitrogen has an overall negative enthalpy of reaction (), the activation energy is very high (). [1] Nitrogenase acts as a catalyst, reducing this energy barrier such that the reaction can take place at ambient temperatures.

A usual assembly consists of two components:

  1. The homodimeric Fe-only protein, the reductase which has a high reducing power and is responsible for a supply of electrons.
  2. The heterotetrameric MoFe protein, a nitrogenase which uses the electrons provided to reduce N2 to NH3. In some assemblies it is replaced by a homologous alternative.
Structure of the FeMo cofactor showing the sites of binding to nitrogenase (the amino acids cys and his). FeMoco cluster.svg
Structure of the FeMo cofactor showing the sites of binding to nitrogenase (the amino acids cys and his).

Reductase

The Fe protein, the dinitrogenase reductase or NifH, is a dimer of identical subunits which contains one [Fe4S4] cluster and has a mass of approximately 60-64kDa. [2] The function of the Fe protein is to transfer electrons from a reducing agent, such as ferredoxin or flavodoxin to the nitrogenase protein. Ferredoxin or flavodoxin can be reduced by one of six mechanisms: 1. by a pyruvate:ferredoxin oxidoreductase, 2. by a bi-directional hydrogenase, 3. in a photosynthetic reaction center, 4. by coupling electron flow to dissipation of the proton motive force, 5. by electron bifurcation, or 6. by a ferredoxin:NADPH oxidoreductase. [3] The transfer of electrons requires an input of chemical energy which comes from the binding and hydrolysis of ATP. The hydrolysis of ATP also causes a conformational change within the nitrogenase complex, bringing the Fe protein and MoFe protein closer together for easier electron transfer. [4]

Nitrogenase

The MoFe protein is a heterotetramer consisting of two α subunits and two β subunits, with a mass of approximately 240-250kDa. [2] The MoFe protein also contains two iron–sulfur clusters, known as P-clusters, located at the interface between the α and β subunits and two FeMo cofactors, within the α subunits. The oxidation state of Mo in these nitrogenases was formerly thought Mo(V), but more recent evidence is for Mo(III). [5] (Molybdenum in other enzymes is generally bound to molybdopterin as fully oxidized Mo(VI)).

Electrons from the Fe protein enter the MoFe protein at the P-clusters, which then transfer the electrons to the FeMo cofactors. Each FeMo cofactor then acts as a site for nitrogen fixation, with N2 binding in the central cavity of the cofactor.

Variations

The MoFe protein can be replaced by alternative nitrogenases in environments low in the Mo cofactor. Two types of such nitrogenases are known: the vanadium–iron (VFe; Vnf) type and the iron–iron (FeFe; Anf) type. Both form an assembly of two α subunits, two β subunits, and two δ (sometimes γ) subunits. The delta subunits are homologous to each other, and the alpha and beta subunits themselves are homologous to the ones found in MoFe nitrogenase. The gene clusters are also homologous, and these subunits are interchangeable to some degree. All nitrogenases use a similar Fe-S core cluster, and the variations come in the cofactor metal. [6] [7]

The Anf nitrogenase in Azotobacter vinelandii is organized in an anfHDGKOR operon. This operon still requires some of the Nif genes to function. An engineered minimal 10-gene operon that incorporates these additional essential genes has been constructed. [8]

Mechanism

Nitrogenase with catalytic sites highlighted. There are two sets of catalytic sites within each nitrogenase enzyme. Correct Cartoon Nitrogenase with Active Sites Highlighted.png
Nitrogenase with catalytic sites highlighted. There are two sets of catalytic sites within each nitrogenase enzyme.
Nitrogenase with one set of metal clusters magnified. Electrons travel from the Fe-S cluster (yellow) to the P cluster (red), and end at the FeMo-co (orange). Cartoon Nitrogenase with Active Site Magnified.png
Nitrogenase with one set of metal clusters magnified. Electrons travel from the Fe-S cluster (yellow) to the P cluster (red), and end at the FeMo-co (orange).

General mechanism

Catalytic sites within nitrogenase. Atoms are colored by element. Top: Fe-S Cluster Middle: P Cluster Bottom: FeMo-co Corrected Nitrogenase Active Sites.jpg
Catalytic sites within nitrogenase. Atoms are colored by element. Top: Fe-S Cluster Middle: P Cluster Bottom: FeMo-co

Nitrogenase is an enzyme responsible for catalyzing nitrogen fixation, which is the reduction of nitrogen (N2) to ammonia (NH3) and a process vital to sustaining life on Earth. [9] There are three types of nitrogenase found in various nitrogen-fixing bacteria: molybdenum (Mo) nitrogenase, vanadium (V) nitrogenase, and iron-only (Fe) nitrogenase. [10] Molybdenum nitrogenase, which can be found in diazotrophs such as legume-associated rhizobia, [11] [12] is the nitrogenase that has been studied the most extensively and thus is the most well characterized. [10] Vanadium nitrogenase and iron-only nitrogenase can both be found in select species of Azotobacter as an alternative nitrogenase. [11] [13] Equations 1 and 2 show the balanced reactions of nitrogen fixation in molybdenum nitrogenase and vanadium nitrogenase respectively.

All nitrogenases are two-component systems made up of Component I (also known as dinitrogenase) and Component II (also known as dinitrogenase reductase). Component I is a MoFe protein in molybdenum nitrogenase, a VFe protein in vanadium nitrogenase, and an Fe protein in iron-only nitrogenase. [9] Component II is a Fe protein that contains the Fe-S cluster., which transfers electrons to Component I. [13] Component I contains 2 metal clusters: the P-cluster, and the FeMo-cofactor (FeMo-co). Mo is replaced by V or Fe in vanadium nitrogenase and iron-only nitrogenase respectively. [9] [15] During catalysis, 2 equivalents of MgATP are hydrolysed which helps to decrease the potential of the to the Fe-S cluster and drive reduction of the P-cluster, and finally to the FeMo-co, where reduction of N2 to NH3 takes place.

Lowe-Thorneley kinetic model

The reduction of nitrogen to two molecules of ammonia is carried out at the FeMo-co of Component I after the sequential addition of proton and electron equivalents from Component II. [9] Steady state, freeze quench, and stopped-flow kinetics measurements carried out in the 70's and 80's by Lowe, Thorneley, and others provided a kinetic basis for this process. [16] [17] The Lowe-Thorneley (LT) kinetic model was developed from these experiments and documents the eight correlated proton and electron transfers required throughout the reaction. [9] [16] [17] Each intermediate stage is depicted as En where n = 0–8, corresponding to the number of equivalents transferred. The transfer of four equivalents are required before the productive addition of N2, although reaction of E3 with N2 is also possible. [16] Notably, nitrogen reduction has been shown to require 8 equivalents of protons and electrons as opposed to the 6 equivalents predicted by the balanced chemical reaction. [18]

Intermediates E0 through E4

Spectroscopic characterization of these intermediates has allowed for greater understanding of nitrogen reduction by nitrogenase, however, the mechanism remains an active area of research and debate. Briefly listed below are spectroscopic experiments for the intermediates before the addition of nitrogen:

E0 – This is the resting state of the enzyme before catalysis begins. EPR characterization shows that this species has a spin of 3/2. [19]

E1 – The one electron reduced intermediate has been trapped during turnover under N2. Mӧssbauer spectroscopy of the trapped intermediate indicates that the FeMo-co is integer spin greater than 1. [20]

Lowe-Thorneley kinetic model for reduction of nitrogen to ammonia by nitrogenase. Lowe-Thorneley Kinetic Model.jpg
Lowe-Thorneley kinetic model for reduction of nitrogen to ammonia by nitrogenase.

E2 – This intermediate is proposed to contain the metal cluster in its resting oxidation state with the two added electrons stored in a bridging hydride and the additional proton bonded to a sulfur atom. Isolation of this intermediate in mutated enzymes shows that the FeMo-co is high spin and has a spin of 3/2. [21]

E3 – This intermediate is proposed to be the singly reduced FeMo-co with one bridging hydride and one hydride. [9]

E4 – Termed the Janus intermediate after the Roman god of transitions, this intermediate is positioned after exactly half of the electron proton transfers and can either decay back to E0 or proceed with nitrogen binding and finish the catalytic cycle. This intermediate is proposed to contain the FeMo-co in its resting oxidation state with two bridging hydrides and two sulfur bonded protons. [9] This intermediate was first observed using freeze quench techniques with a mutated protein in which residue 70, a valine amino acid, is replaced with isoleucine. [22] This modification prevents substrate access to the FeMo-co. EPR characterization of this isolated intermediate shows a new species with a spin of ½. ENDOR experiments have provided insight into the structure of this intermediate, revealing the presence of two bridging hydrides. [22] 95Mo and 57Fe ENDOR show that the hydrides bridge between two iron centers. [23] Cryoannealing of the trapped intermediate at -20 °C results in the successive loss of two hydrogen equivalents upon relaxation, proving that the isolated intermediate is consistent with the E4 state. [9] The decay of E4 to E2 + H2 and finally to E0 and 2H2 has confirmed the EPR signal associated with the E2 intermediate. [9]

The above intermediates suggest that the metal cluster is cycled between its original oxidation state and a singly reduced state with additional electrons being stored in hydrides. It has alternatively been proposed that each step involves the formation of a hydride and that the metal cluster actually cycles between the original oxidation state and a singly oxidized state. [9]

Distal and alternating pathways for N2 fixation

Distal vs. alternating mechanistic pathways for nitrogen fixation in nitrogenase. N2-fixation-mech.jpg
Distal vs. alternating mechanistic pathways for nitrogen fixation in nitrogenase.

While the mechanism for nitrogen fixation prior to the Janus E4 complex is generally agreed upon, there are currently two hypotheses for the exact pathway in the second half of the mechanism: the "distal" and the "alternating" pathway. [9] [24] [25] In the distal pathway, the terminal nitrogen is hydrogenated first, releases ammonia, then the nitrogen directly bound to the metal is hydrogenated. In the alternating pathway, one hydrogen is added to the terminal nitrogen, then one hydrogen is added to the nitrogen directly bound to the metal. This alternating pattern continues until ammonia is released. [9] [24] [25] Because each pathway favors a unique set of intermediates, attempts to determine which path is correct have generally focused on the isolation of said intermediates, such as the nitrido in the distal pathway, [26] and the diazene and hydrazine in the alternating pathway. [9] Attempts to isolate the intermediates in nitrogenase itself have so far been unsuccessful, but the use of model complexes has allowed for the isolation of intermediates that support both sides depending on the metal center used. [9] Studies with Mo generally point towards a distal pathway, while studies with Fe generally point towards an alternating pathway. [9] [24] [25] [27] [28]

Specific support for the distal pathway has mainly stemmed from the work of Schrock and Chatt, who successfully isolated the nitrido complex using Mo as the metal center in a model complex. [26] [29] Specific support for the alternating pathway stems from a few studies. Iron only model clusters have been shown to catalytically reduce N2. [27] [28] Small tungsten clusters have also been shown to follow an alternating pathway for nitrogen fixation. [30] The vanadium nitrogenase releases hydrazine, an intermediate specific to the alternating mechanism. [9] [31] However, the lack of characterized intermediates in the native enzyme itself means that neither pathway has been definitively proven. Furthermore, computational studies have been found to support both sides, depending on whether the reaction site is assumed to be at Mo (distal) or at Fe (alternating) in the MoFe cofactor. [9] [24] [25]

Mechanism of MgATP binding

Binding of MgATP by nitrogenase.png

Binding of MgATP is one of the central events to occur in the mechanism employed by nitrogenase. Hydrolysis of the terminal phosphate group of MgATP provides the energy needed to transfer electrons from the Fe protein to the MoFe protein. [32] The binding interactions between the MgATP phosphate groups and the amino acid residues of the Fe protein are well understood by comparing to similar enzymes, while the interactions with the rest of the molecule are more elusive due to the lack of a Fe protein crystal structure with MgATP bound (as of 1996). [33] Three protein residues have been shown to have significant interactions with the phosphates. [16] In the absence of MgATP, a salt bridge exists between residue 15, lysine, and residue 125, aspartic acid. [33] Upon binding, this salt bridge is interrupted. Site-specific mutagenesis has demonstrated that when the lysine is substituted for a glutamine, the protein's affinity for MgATP is greatly reduced [34] and when the lysine is substituted for an arginine, MgATP cannot bind due to the salt bridge being too strong. [35] The necessity of specifically aspartic acid at site 125 has been shown through noting altered reactivity upon mutation of this residue to glutamic acid. [36] Residue 16, serine, has been shown to bind MgATP. Site-specific mutagenesis was used to demonstrate this fact. [36] This has led to a model in which the serine remains coordinated to the Mg2+ ion after phosphate hydrolysis in order to facilitate its association with a different phosphate of the now ADP molecule. [37] MgATP binding also induces significant conformational changes within the Fe protein. [16] Site-directed mutagenesis was employed to create mutants in which MgATP binds but does not induce a conformational change. [38] Comparing X-ray scattering data in the mutants versus in the wild-type protein led to the conclusion that the entire protein contracts upon MgATP binding, with a decrease in radius of approximately 2.0 Å. [38]

Other mechanistic details

Many mechanistic aspects of catalysis remain unknown. No crystallographic analysis has been reported on substrate bound to nitrogenase.

Nitrogenase is able to reduce acetylene, but is inhibited by carbon monoxide, which binds to the enzyme and thereby prevents binding of dinitrogen. Dinitrogen prevent acetylene binding, but acetylene does not inhibit binding of dinitrogen and requires only one electron for reduction to ethylene. [39] Due to the oxidative properties of oxygen, most nitrogenases are irreversibly inhibited by dioxygen, which degradatively oxidizes the Fe-S cofactors.[ citation needed ] This requires mechanisms for nitrogen fixers to protect nitrogenase from oxygen in vivo . Despite this problem, many use oxygen as a terminal electron acceptor for respiration.[ citation needed ] Although the ability of some nitrogen fixers such as Azotobacteraceae to employ an oxygen-labile nitrogenase under aerobic conditions has been attributed to a high metabolic rate, allowing oxygen reduction at the cell membrane, the effectiveness of such a mechanism has been questioned at oxygen concentrations above 70 μM (ambient concentration is 230 μM O2), as well as during additional nutrient limitations. [40] A molecule found in the nitrogen-fixing nodules of leguminous plants, leghemoglobin, which can bind to dioxygen via a heme prosthetic group, plays a crucial role in buffering O2 at the active site of the nitrogenase, while concomitantly allowing for efficient respiration. [41]

Nonspecific reactions

In addition to dinitrogen reduction, nitrogenases also reduce protons to dihydrogen, meaning nitrogenase is also a dehydrogenase. A list of other reactions carried out by nitrogenases is shown below: [42] [43]

HC≡CH → H2C=CH2
N–=N+=O → N2 + H2O
N=N=N– → N2 + NH3
C≡N−
 → CH4, NH3, H3C–CH3, H2C=CH2 (CH3NH2)
N≡C–R → RCH3 + NH3
C≡N–R → CH4, H3C–CH3, H2C=CH2, C3H8, C3H6, RNH2
O=C=S → CO + H2S [44] [45]
O=C=O → CO + H2O [44]
S=C=N– → H2S + HCN [45]
O=C=N– → H2O + HCN, CO + NH3 [45]

Furthermore, dihydrogen functions as a competitive inhibitor, [46] carbon monoxide functions as a non-competitive inhibitor, [42] [43] and carbon disulfide functions as a rapid-equilibrium inhibitor [44] of nitrogenase.

Vanadium nitrogenases have also been shown to catalyze the conversion of CO into alkanes through a reaction comparable to Fischer-Tropsch synthesis.

Organisms that synthesize nitrogenase

There are two types of bacteria that synthesize nitrogenase and are required for nitrogen fixation. These are:

Similarity to other proteins

The three subunits of nitrogenase exhibit significant sequence similarity to three subunits of the light-independent version of protochlorophyllide reductase that performs the conversion of protochlorophyllide to chlorophyll. This protein is present in gymnosperms, algae, and photosynthetic bacteria but has been lost by angiosperms during evolution. [47]

Separately, two of the nitrogenase subunits (NifD and NifH) have homologues in methanogens that do not fix nitrogen e.g. Methanocaldococcus jannaschii . [48] Little is understood about the function of these "class IV" nif genes, [49] though they occur in many methanogens. In M. jannaschii they are known to interact with each other and are constitutively expressed. [48]

Measurement of nitrogenase activity

As with many assays for enzyme activity, it is possible to estimate nitrogenase activity by measuring the rate of conversion of the substrate (N2) to the product (NH3). Since NH3 is involved in other reactions in the cell, it is often desirable to label the substrate with 15N to provide accounting or "mass balance" of the added substrate. A more common assay, the acetylene reduction assay or ARA, estimates the activity of nitrogenase by taking advantage of the ability of the enzyme to reduce acetylene gas to ethylene gas. These gases are easily quantified using gas chromatography. [50] Though first used in a laboratory setting to measure nitrogenase activity in extracts of Clostridium pasteurianum cells, ARA has been applied to a wide range of test systems, including field studies where other techniques are difficult to deploy. For example, ARA was used successfully to demonstrate that bacteria associated with rice roots undergo seasonal and diurnal rhythms in nitrogenase activity, which were apparently controlled by the plant. [51]

Unfortunately, the conversion of data from nitrogenase assays to actual moles of N2 reduced (particularly in the case of ARA), is not always straightforward and may either underestimate or overestimate the true rate for a variety of reasons. For example, H2 competes with N2 but not acetylene for nitrogenase (leading to overestimates of nitrogenase by ARA). Bottle or chamber-based assays may produce negative impacts on microbial systems as a result of containment or disruption of the microenvironment through handling, leading to underestimation of nitrogenase. Despite these weaknesses, such assays are very useful in assessing relative rates or temporal patterns in nitrogenase activity.

See also

Related Research Articles

Nitrogen fixation is a chemical process by which molecular dinitrogen is converted into ammonia. It occurs both biologically and abiologically in chemical industries. Biological nitrogen fixation or diazotrophy is catalyzed by enzymes called nitrogenases. These enzyme complexes are encoded by the Nif genes and contain iron, often with a second metal.

<span class="mw-page-title-main">Metalloprotein</span> Protein that contains a metal ion cofactor

Metalloprotein is a generic term for a protein that contains a metal ion cofactor. A large proportion of all proteins are part of this category. For instance, at least 1000 human proteins contain zinc-binding protein domains although there may be up to 3000 human zinc metalloproteins.

Diazotrophs are bacteria and archaea that fix atmospheric nitrogen (N2) in the atmosphere into bioavailable forms such as ammonia.

<i>Azotobacter</i> Genus of bacteria

Azotobacter is a genus of usually motile, oval or spherical bacteria that form thick-walled cysts and may produce large quantities of capsular slime. They are aerobic, free-living soil microbes that play an important role in the nitrogen cycle in nature, binding atmospheric nitrogen, which is inaccessible to plants, and releasing it in the form of ammonium ions into the soil. In addition to being a model organism for studying diazotrophs, it is used by humans for the production of biofertilizers, food additives, and some biopolymers. The first representative of the genus, Azotobacter chroococcum, was discovered and described in 1901 by Dutch microbiologist and botanist Martinus Beijerinck. Azotobacter species are Gram-negative bacteria found in neutral and alkaline soils, in water, and in association with some plants.

Azotobacter vinelandii is Gram-negative diazotroph that can fix nitrogen while grown aerobically. These bacteria are easily cultured and grown.

Microbial metabolism is the means by which a microbe obtains the energy and nutrients it needs to live and reproduce. Microbes use many different types of metabolic strategies and species can often be differentiated from each other based on metabolic characteristics. The specific metabolic properties of a microbe are the major factors in determining that microbe's ecological niche, and often allow for that microbe to be useful in industrial processes or responsible for biogeochemical cycles.

<span class="mw-page-title-main">Transition metal dinitrogen complex</span> Coordination compounds with N2

Transition metal dinitrogen complexes are coordination compounds that contain transition metals as ion centers the dinitrogen molecules (N2) as ligands.

<span class="mw-page-title-main">Formate dehydrogenase</span>

Formate dehydrogenases are a set of enzymes that catalyse the oxidation of formate to carbon dioxide, donating the electrons to a second substrate, such as NAD+ in formate:NAD+ oxidoreductase (EC 1.17.1.9) or to a cytochrome in formate:ferricytochrome-b1 oxidoreductase (EC 1.2.2.1). This family of enzymes has attracted attention as inspiration or guidance on methods for the carbon dioxide fixation, relevant to global warming.

The nif genes are genes encoding enzymes involved in the fixation of atmospheric nitrogen into a form of nitrogen available to living organisms. The primary enzyme encoded by the nif genes is the nitrogenase complex which is in charge of converting atmospheric nitrogen (N2) to other nitrogen forms such as ammonia which the organism can use for various purposes. Besides the nitrogenase enzyme, the nif genes also encode a number of regulatory proteins involved in nitrogen fixation. The nif genes are found in both free-living nitrogen-fixing bacteria and in symbiotic bacteria associated with various plants. The expression of the nif genes is induced as a response to low concentrations of fixed nitrogen and oxygen concentrations (the low oxygen concentrations are actively maintained in the root environment of host plants). The first Rhizobium genes for nitrogen fixation (nif) and for nodulation (nod) were cloned in the early 1980s by Gary Ruvkun and Sharon R. Long in Frederick M. Ausubel's laboratory.

Nitrogenase (flavodoxin) (EC 1.19.6.1) is an enzyme with systematic name reduced flavodoxin:dinitrogen oxidoreductase (ATP-hydrolysing). This enzyme catalyses the following chemical reaction

<span class="mw-page-title-main">Vanadium nitrogenase</span> Enzyme necessary for the process of nitrogen fixation

Vanadium nitrogenase is a key enzyme for nitrogen fixation found in nitrogen-fixing bacteria, and is used as an alternative to molybdenum nitrogenase when molybdenum is unavailable. Vanadium nitrogenases are an important biological use of vanadium, which is uncommonly used by life. An important component of the nitrogen cycle, vanadium nitrogenase converts nitrogen gas to ammonia, thereby making otherwise inaccessible nitrogen available to plants. Unlike molybdenum nitrogenase, vanadium nitrogenase can also reduce carbon monoxide to ethylene, ethane and propane but both enzymes can reduce protons to hydrogen gas and acetylene to ethylene.

<span class="mw-page-title-main">Nif regulon</span>

The Nif regulon is a set of seven operons used to regulate nitrogen fixation in the coliform bacterium Klebsiella pneumoniae under anaerobic and microaerophilic conditions. It includes 17 nif genes, and is situated between the his and the Shi-A operon of the bacterium.

<span class="mw-page-title-main">Bis(dinitrogen)bis(1,2-bis(diphenylphosphino)ethane)molybdenum(0)</span> Chemical compound

trans-Bis(dinitrogen)bis[1,2-bis(diphenylphosphino)ethane]molybdenum(0) is a coordination complex with the formula Mo(N2)2(dppe)2. It is a relatively air stable yellow-orange solid. It is notable as being the first discovered dinitrogen containing complex of molybdenum.

<i>Methanococcus maripaludis</i> Species of archaeon

Methanococcus maripaludis is a species of methanogenic archaea found in marine environments, predominantly salt marshes. M. maripaludis is a non-pathogenic, gram-negative, weakly motile, non-spore-forming, and strictly anaerobic mesophile. It is classified as a chemolithoautotroph. This archaeon has a pleomorphic coccoid-rod shape of 1.2 by 1.6 μm, in average size, and has many unique metabolic processes that aid in survival. M. maripaludis also has a sequenced genome consisting of around 1.7 Mbp with over 1,700 identified protein-coding genes. In ideal conditions, M. maripaludis grows quickly and can double every two hours.

<span class="mw-page-title-main">FeMoco</span> Cofactor of nitrogenase

FeMoco (FeMo cofactor) is the primary cofactor of nitrogenase. Nitrogenase is the enzyme that catalyzes the conversion of atmospheric nitrogen molecules N2 into ammonia (NH3) through the process known as nitrogen fixation. Because it contains iron and molybdenum, the cofactor is called FeMoco. Its stoichiometry is Fe7MoS9C.

Evolution of metal ions in biological systems refers to the incorporation of metallic ions into living organisms and how it has changed over time. Metal ions have been associated with biological systems for billions of years, but only in the last century have scientists began to truly appreciate the scale of their influence. Major and minor metal ions have become aligned with living organisms through the interplay of biogeochemical weathering and metabolic pathways involving the products of that weathering. The associated complexes have evolved over time.

<span class="mw-page-title-main">Tris(trimethylsilyl)amine</span> Chemical compound

Tris(trimethylsilyl)amine is the simplest tris(trialkylsilyl)amine which are having the general formula (R3Si)3N, in which all three hydrogen atoms of the ammonia are replaced by trimethylsilyl groups (-Si(CH3)3). Tris(trimethylsilyl)amine has been for years in the center of scientific interest as a stable intermediate in chemical nitrogen fixation (i. e. the conversion of atmospheric nitrogen N2 into organic substrates under normal conditions).

Serena DeBeer is an American chemist. She is currently a W3-Professor and the director at the Max Planck Institute for Chemical Energy Conversion in Muelheim an der Ruhr, Germany, where she heads the Department of Inorganic Spectroscopy. Her expertise lies in the application and development of X-ray based spectroscopic methods as probes of electronic structure in biological and chemical catalysis.

<span class="mw-page-title-main">Abiological nitrogen fixation using homogeneous catalysts</span> Chemical process that converts nitrogen to ammonia

Abiological nitrogen fixation describes chemical processes that fix (react with) N2, usually with the goal of generating ammonia. The dominant technology for abiological nitrogen fixation is the Haber process, which uses iron-based heterogeneous catalysts and H2 to convert N2 to NH3. This article focuses on homogeneous (soluble) catalysts for the same or similar conversions.

<span class="mw-page-title-main">Molybdenum in biology</span> Use of molybdenum by organisms

Molybdenum is an essential element in most organisms. It is most notably present in nitrogenase which is an essential part of nitrogen fixation.

References

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