Insertion Of Molybdenum Research Articles

Material Plasma Exposure eXperiment (MPEX) High Heat Flux Bellows for Component Alignment in High Microwave Environment

The Material Plasma Exposure eXperiment (MPEX) device is a linear plasma device developed to perform plasma material interaction experiments under the conditions prototypic of a fusion reactor divertor. MPEX has multiple systems that must be precisely aligned to the plasma axis, including an electron cyclotron heating system that emits up to 400 kW of microwave power into the vacuum vessel. Five distinct systems require precise alignment on the MPEX device, thus requiring four bellows, all of which are adjacent to the plasma at a relatively high heat flux of approximately 47 kW/m2 and microwave power regions. The MPEX high heat flux bellows (HHFB) is designed to deliver 6 degrees of freedom positioning. The HHFB includes titanium–zirconium–molybdenum (TZM) inserts that are brazed into a Glidcop AL-15 body using a high-temperature braze alloy, thus blocking direct line of sight to an edge-welded bellows from the plasma and microwave screen to block microwaves from the bellows. A custom ConFlat knife edge is machined into the Glidcop AL-15, so the vacuum flanges do not need a braze or weld joint on the vacuum interface. Fingerstock or copper mesh is used to restrict microwave power from entering the interstitial space between the water-cooled Glidcop AL-15 body and edge-welded bellows. Glidcop AL-15 was selected as the material of choice for the water-cooled body because it can maintain mechanical integrity at elevated temperatures, and it also allows for a high-temperature braze. TZM was selected for its machinability and compatibility with vacuum and plasma requirements. A test article is also being considered for a similarly shaped component, the MPEX limiter, that will demonstrate the integrity of the braze joint under high thermal load. Results from this testing will be extrapolated to deduce the lifetime and integrity of the HHFB design.

Characterization of the Nickel‐inserting Cyclometallase LarC from Moorella thermoacetica and Identification of a CMPylated Reaction Intermediate

The nickel‐pincer nucleotide (NPN) cofactor is required for lactate racemase (LarA) activity1, and LarB, LarE, and LarC are needed to generate this coenzyme2. LarC catalyzes the last step of the biosynthesis pathway by inserting nickel into pyridinium‐3,5‐dithiocarboxylic acid mononucleotide (P2TMN), resulting in the mature NPN cofactor3. Previously, LarC from Lactobacillus plantarum was shown to be a CTP‐dependent, single‐turnover nickel insertase or cyclometallase, but a structure was only obtained for its C‐terminal domain and its reaction mechanism was not identified. We characterized LarC from Moorella thermoacetica(LarCMt) and identified a novel reaction intermediate in which the precursor P2TMN is CMPylated. We propose that LarCMt uses CTP to generate the CMP‐P2TMN species that is properly positioned in the active site for nickel insertion, analogous to the molybdenum insertion step during molybdenum cofactor biosynthesis4. LarCMt variants were characterized to further elucidate the mechanism of the transient CMPylation process. Additionally, we generated preliminary structural data for the full‐length LarCMt through cryo‐electron microscopy. Our results highlight the role of CTP in the nickel insertion reaction and provide a better structural and mechanistic understanding of the LarC reaction.1. Desguin, B. et al. A tethered niacin‐derived pincer complex with a nickel‐carbon bond in lactate racemase. Science. 349, 66–69 (2015).2. Desguin, B. et al. Lactate racemase is a nickel‐dependent enzyme activated by a widespread maturation system. Nat. Commun. 5, 3615 (2014).3. Desguin, B. et al. Biosynthesis of the nickel‐pincer nucleotide cofactor of lactate racemase requires a CTP‐dependent cyclometallase. J. Biol. Chem. 293, 12303–12317 (2018).4. Llamas, A., Mendel, R. R. & Schwarz, G. Synthesis of adenylated molybdopterin: An essential step for molybdenum insertion. J. Biol. Chem. 279, 55241–55246 (2004).

Tracing the incorporation of the "ninth sulfur" into the nitrogenase cofactor precursor with selenite and tellurite.

The Mo-nitrogenase catalyzes the reduction of N2 to NH3 at its cofactor, an [(R-homocitrate)MoFe7S9C] cluster synthesized via the formation of a [Fe8S9C] L-cluster prior to the insertion of Mo and homocitrate. Previously, we have identified a [Fe8S8C] L*-cluster, which is homologous to the core structure of the L-cluster but lacks the ‘9th sulfur’ in the belt region. However, direct evidence and mechanistic details of the L*- to L-cluster conversion upon ‘9th sulfur’ insertion remain elusive. Here, we trace the ‘9th sulfur’ insertion using SeO32− and TeO32− as ‘labeled’ SO32−. Biochemical, EPR and XAS/EXAFS studies suggest a role of the ‘9th sulfur’ in cluster transfer during cofactor biosynthesis while revealing the incorporation of Se2−- and Te2−-like species into the L-cluster. DFT calculations further point to a plausible mechanism involving in-situ reduction of SO32− to S2−, thereby suggesting the utility of this reaction to label the catalytically-important belt region for mechanistic investigations of nitrogenase.

Effect on the Mechanical Properties of Grey Cast Iron with Variation of Molybdenum and AS – Cast Alloying Elements

Metal casting is a predominant manufacturing advancement for adeptly fabricating components with complicated shapes. Many of the industrial castings produced are made from steel and iron alloys with attractive properties and less production cost. In this research work, the effect of molybdenum addition to class 30 type grey cast iron for the production of high performance cast iron (HPCI) has been carried out. Molybdenum inclusion not only refines the majority of graphite flakes but also increases the length of a small fraction of graphite flakes and improves the thermal conductivity by a percentage up to 2.2% fixed as per the research conducted, while excessive molybdenum insertion not only induces precipitation and solution reinforcement but it will also enhance the ultimate tensile strength (UTS) and hardness. According to research conducted, it was proved that molybdenum inclusion of 120 gm showed a functional way to spread HPCI with enhancing mechanical and thermal properties in grey cast iron when compared to other percentages of molybdenum used and also the average difference in the percentage of hardness in each type of molybdenum sample is about 5 to 10 %. Finally, after the tests, it was also predicted that the molybdenum's hardenability property was beneficial for white cast iron production which will rise the wear resistance property.

Impact of uranium oxide (UO2) fuel with molybdenum (Mo) inserts on pressurized water reactor performance and safety

This work investigates nuclear reactor performance and safety characteristics of UO2 with high thermal conductivity Mo insert structures by using multiphysics modeling techniques. The purpose of this study is to use scoping analyses to quantify the impact of using Mo inserts from neutronic and heat transfer standpoints. Attention is given to reactor performance parameters, such as cycle length, maximum fuel temperature, temperature gradients in the fuel, and stored energy in the fuel. The finite-element code BISON and the Monte Carlo particle transport code Serpent were used to perform sensitivity analyses on the Mo insert geometry to optimize the insert design and inform larger scale modeling that required the homogenization of the UO2 and Mo. Although BISON is often used as a fuel performance analysis tool, it is used in this context for heat transfer analysis only. Fuel performance optimization is outside the scope of the current study, but would be important for future work focused on this concept. The results showed that the insert had little impact on neutronic performance and that homogenizing the UO2 and Mo was acceptable for reactor physics calculations. Reactivity temperature coefficients calculated using homogeneous UO2-Mo were shown to be relatively similar to UO2, but higher Mo content and 235U enrichment can reduce the worth of soluble boron and control rods. The effect of insert geometry on heat transfer was much greater, and an approximately 15–20% difference in maximum fuel temperature was predicted between the best and worst performing heat transfer geometries. Thermal conductivity calibration based on the finite element analysis results was performed to improve the accuracy of temperature predictions in reactor analysis models that homogenized the UO2-Mo fuel. Compared with UO2 in a pressurized water reactor (PWR), the optimized UO2-Mo design increased the margin to fuel melt by 13–32% across the fuel cycle, but it requires the 235U enrichment to exceed 5% to match the cycle length of conventional UO2.

Critical Raw Material-Free Catalysts and Electrocatalysts: Complementary Strategies to Activate Economic, Robust, and Ecofriendly SrTiO3

In this contribution, new SrTiO3-based materials have been developed and their catalytic and electrocatalytic properties have been tuned by cation insertion, nanocomposition, and infiltration. The aim is to develop highly functional materials within a critical raw material-free approach with a particular aim toward durability and stability [under operating conditions of solid oxide fuel cell (SOFC) anodes] and activity toward biogas. We started from a sustainable and durable perovskite, SrTiO3, with the aim of implementing performances with insertion of Ba and Mo into the crystalline cell. The catalysts are BaxSr1–xTi1–yMoyO3, with x = 0 and 0.5 and y = 0, 0.1, and 0.4. Water-based wet chemistry procedures were developed specifically for each compound to obtain high purity and control barium and molybdenum insertion into the perovskite lattice. This result has been successfully obtained by means of a detailed characterization (X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, temperature-programmed desorption, temperature-programmed reduction, and BrunauerEmmettTeller) carried out during each preparation steps. We demonstrated that catalytic (methane dry reforming and CO oxidation is obtained with SrTi0.9Mo0.1O3) and electrocatalytic (of SrTi0.6Mo0.4O3 as the anode in SOFCs) activities can be developed starting from an economic, sustainable, and robust material. Activity enhancement was obtained with nickel nanodeposition (wet impregnation and infiltration).

Conductive inserts to reduce nuclear fuel temperature

In an effort to develop better performing nuclear fuels, placement of conductive inserts in nuclear fuel pellets is being considered. Conductive inserts incorporated in the fuel pellets will dissipate heat more efficiently, allowing the fuel to operate at a lower temperature while producing the same amount of power. Calculation results reported in the present paper, show that placing a 6-finned molybdenum insert in a UO2 pellet will result in an 842 C reduction of the peak fuel temperature. Likewise, placing multiple equidistantly spaced 50 μm thick molybdenum discs in a UO2 pellet will result in a 995 C reduction of the peak fuel temperature. In both cases, the volume of the insert is limited to 5% of the volume of the pellet. While these results are preliminary in scope, the impact of the reduced peak temperature on expected fuel performance warrants initiation of experimental work that will include fabrication and irradiation of these and similar fuel designs at the Idaho National Laboratory.

Optimization of high heat flux components for DIII-D neutral beam upgrades

Upgrade of the DIII-D neutral beams leads to enhanced heat loads on many components, such as calorimeter, collimator, and pole shields which protect neutral beam magnets. Power increase from 2.6 MW to 3.2 MW per source leads to a normal heat flux loads of up to 55 MW/m2 for the calorimeter. The Princeton Plasma Physics Laboratory is responsible for the design and manufacturing of the upgrades of these components.Heat flux distribution on neutral beam components is very uneven and leads to significant thermal stresses. High heat flux density impact requires surface optimization to reduce surface heat flux projection, and avoid localized melting. Several new design features were introduced to accommodate increased heat loads, such as molybdenum inserts for the pole shields, two-dimensional shaping for the calorimeter, and three-dimensional shape optimization and replaceable copper inserts for the collimator. Additionally, all three components include an optimized cooling system design featuring peripheral cooling of copper components.The optimization process included applying analytical relations for the transient temperature distributions on the high heat flux components. These relations were confirmed by previous DIII-D experimental results. To validate the designs, numerical simulations were performed. Results of the design optimization and numerical simulations will be presented.

Corrosion of defective molybdenum insert in liquid glass as the main reason of accident at glass-melting furnace

Abstract The main reason of an accident at the Piskivka glass plant (Kyiv region, Ukraine) was in failure and degradation of a molybdenum insert in refractory REFEL 1240 FVMo block in the throat of glass-melting furnace. Using the analysis of literature data and the available data obtained at the plant, it was shown that this should be preceded by active degradation and blurring of the refractory AZS. Failure analysis of the fractured molybdenum insert was carried out experimentally by light microscopy, scanning electron microscopy and X-ray diffraction. It was suggested that the degradation was caused by the intergranular corrosion that took place at high temperature due to the formation of Mo Ni and Mo Ni Fe liquid eutectics along grain boundaries. The piece of molybdenum was most probably contaminated by Ni and Fe from the tools used during the processing of molybdenum insert by hot deformation. As a result, liquid glass had been penetrated through the weakened grain boundaries and initially “washed out” some grains from the surface and then crushed the inside boundaries.

Shared function and moonlighting proteins in molybdenum cofactor biosynthesis.

The biosynthesis of the molybdenum cofactor (Moco) is a highly conserved pathway in bacteria, archaea and eukaryotes. The molybdenum atom in Moco-containing enzymes is coordinated to the dithiolene group of a tricyclic pyranopterin monophosphate cofactor. The biosynthesis of Moco can be divided into three conserved steps, with a fourth present only in bacteria and archaea: (1) formation of cyclic pyranopterin monophosphate, (2) formation of molybdopterin (MPT), (3) insertion of molybdenum into MPT to form Mo-MPT, and (4) additional modification of Mo-MPT in bacteria with the attachment of a GMP or CMP nucleotide, forming the dinucleotide variants of Moco. While the proteins involved in the catalytic reaction of each step of Moco biosynthesis are highly conserved among the Phyla, a surprising link to other cellular pathways has been identified by recent discoveries. In particular, the pathways for FeS cluster assembly and thio-modifications of tRNA are connected to Moco biosynthesis by sharing the same protein components. Further, proteins involved in Moco biosynthesis are not only shared with other pathways, but additionally have moonlighting roles. This review gives an overview of Moco biosynthesis in bacteria and humans and highlights the shared function and moonlighting roles of the participating proteins.

Thermal management of tungsten leading edges in DIII-D

The DiMES materials probe exposed tungsten blocks with 0.3 and 1mm high leading edges to DIII-D He plasmas in 2015 and 2016 viewed with high resolution IRTV. The 1-mm edge may have reached >3000°C in a 3-s shot with a (parallel) heat load of ∼80MW/m2 and ∼8.6MW/m2 on the surface based on modeling. The experiments support ITER. Leading edges were also a concern in the DIII-D Metal Tile Experiment in 2016. Two toroidal arrays of divertor tiles had W-coated molybdenum inserts 50mm wide radially. This paper presents data and thermal analyses.

Characterization of Mo-AlNxOy Thin Films Deposited by RF Magnetron Sputtering

Thin films of Mo-AlNxOy were grown on glass and silicon substrates by RF-reactive magnetron sputtering. The substrate deposition temperature was varied with the purpose of evaluating the composition variation, crystal structure, reflectance, absorptance and band gap of the films. The results showed that the most amorphous films presented the highest absorptance. The absorptance increase and the band gap reduction are due to the crystallinity and the molybdenum insertion. This change occurred due to the different behavior of band gap amorphous materials, the electron acceptors/donors increase and plasmon effect caused by molybdenum insertion.

DIII-D Neutral Beam Pole Shields Design Including Copper Plate with Removable Molybdenum Insert

The neutral beam copper pole shields currently in service at DIII-D have experienced localized melting and fatigue cracks in the grooves machined in the back of the copper plates. Higher power is now desired out of the neutral beams, requiring a pole shield upgrade to handle the elevated thermal load. The Princeton Plasma Physics Laboratory is responsible for the design and manufacturing of the pole shield upgrade.Since the heat flux on the pole shield is highly localized, the new design includes a molybdenum insert, positioned in the area of the maximum thermal loading, mounted in the copper plate, which is cooled by a single cooling channel. A ten segment design was implemented, with loose tongue and groove connections, to allow in situ assembly and maintenance.To validate the design, numerical simulations were performed using ANSYS workbench and consisted of two stages: 1. during the first stage unsteady fluid flow simulation was performed in conjunction with heat transfer analysis in the insert, copper plate, and water cooling system; 2. during the second stage, the temperature distribution was used to specify thermal strains, and perform transient structural analysis.

The biosynthesis of the molybdenum cofactors.

The biosynthesis of the molybdenum cofactors (Moco) is an ancient, ubiquitous, and highly conserved pathway leading to the biochemical activation of molybdenum. Moco is the essential component of a group of redox enzymes, which are diverse in terms of their phylogenetic distribution and their architectures, both at the overall level and in their catalytic geometry. A wide variety of transformations are catalyzed by these enzymes at carbon, sulfur and nitrogen atoms, which include the transfer of an oxo group or two electrons to or from the substrate. More than 50 molybdoenzymes were identified to date. In all molybdoenzymes except nitrogenase, molybdenum is coordinated to a dithiolene group on the 6-alkyl side chain of a pterin called molybdopterin (MPT). The biosynthesis of Moco can be divided into three general steps, with a fourth one present only in bacteria and archaea: (1) formation of the cyclic pyranopterin monophosphate, (2) formation of MPT, (3) insertion of molybdenum into molybdopterin to form Moco, and (4) additional modification of Moco in bacteria with the attachment of a nucleotide to the phosphate group of MPT, forming the dinucleotide variant of Moco. This review will focus on the biosynthesis of Moco in bacteria, humans and plants.

The Sulfur Carrier Protein TusA Has a Pleiotropic Role in Escherichia coli That Also Affects Molybdenum Cofactor Biosynthesis*

The Escherichia coli L-cysteine desulfurase IscS mobilizes sulfur from L-cysteine for the synthesis of several biomolecules such as iron-sulfur (FeS) clusters, molybdopterin, thiamin, lipoic acid, biotin, and the thiolation of tRNAs. The sulfur transfer from IscS to various biomolecules is mediated by different interaction partners (e.g. TusA for thiomodification of tRNAs, IscU for FeS cluster biogenesis, and ThiI for thiamine biosynthesis/tRNA thiolation), which bind at different sites of IscS. Transcriptomic and proteomic studies of a ΔtusA strain showed that the expression of genes of the moaABCDE operon coding for proteins involved in molybdenum cofactor biosynthesis is increased under aerobic and anaerobic conditions. Additionally, under anaerobic conditions the expression of genes encoding hydrogenase 3 and several molybdoenzymes such as nitrate reductase were also increased. On the contrary, the activity of all molydoenzymes analyzed was significantly reduced in the ΔtusA mutant. Characterization of the ΔtusA strain under aerobic conditions showed an overall low molybdopterin content and an accumulation of cyclic pyranopterin monophosphate. Under anaerobic conditions the activity of nitrate reductase was reduced by only 50%, showing that TusA is not essential for molybdenum cofactor biosynthesis. We present a model in which we propose that the direction of sulfur transfer for each sulfur-containing biomolecule is regulated by the availability of the interaction partner of IscS. We propose that in the absence of TusA, more IscS is available for FeS cluster biosynthesis and that the overproduction of FeS clusters leads to a modified expression of several genes.

X-ray Spectroscopic Observation of an Interstitial Carbide in NifEN-Bound FeMoco Precursor

The iron-molybdenum cofactor (FeMoco) of nitrogenase contains a biologically unprecedented μ(6)-coordinated C(4-) ion. Although the role of this interstitial atom in nitrogenase catalysis is unknown, progress in understanding its biosynthetic origins has been made. Here we report valence-to-core Fe Kβ X-ray emission spectroscopy data to show that this C(4-) ion is present in the Fe(8)S(9) "L-cluster," which is the immediate precursor to FeMoco prior to the insertion of molybdenum and coordination by homocitrate. These results accord with recent evidence supporting a role for the S-adenosylmethionine-dependent enzyme NifB in the incorporation of carbon into the FeMoco center of nitrogenase.

Heavy metal ions inhibit molybdoenzyme activity by binding to the dithiolene moiety of molybdopterin in Escherichia coli

Molybdenum insertion into the dithiolene group on the 6-alkyl side-chain of molybdopterin is a highly specific process that is catalysed by the MoeA and MogA proteins in Escherichia coli. Ligation of molybdate to molybdopterin generates the molybdenum cofactor, which can be inserted directly into molybdoenzymes binding the molybdopterin form of the molybdenum cofactor, or is further modified in bacteria to form the dinucleotide form of the molybdenum cofactor. The ability of various metals to bind tightly to sulfur-rich sites raised the question of whether other metal ions could be inserted in place of molybdenum at the dithiolene moiety of molybdopterin in molybdoenzymes. We used the heterologous expression systems of human sulfite oxidase and Rhodobacter sphaeroides dimethylsulfoxide reductase in E. coli to study the incorporation of different metal ions into the molybdopterin site of these enzymes. From the added metal-containing compounds Na(2)MoO(4), Na(2)WO(4), NaVO(3), Cu(NO(3))(2), CdSO(4) and NaAsO(2) during the growth of E. coli, only molybdate and tungstate were specifically inserted into sulfite oxidase and dimethylsulfoxide reductase. Other metals, such as copper, cadmium and arsenite, were nonspecifically inserted into sulfite oxidase, but not into dimethylsulfoxide reductase. We showed that metal insertion into molybdopterin occurs beyond the step of molybdopterin synthase and is independent of MoeA and MogA proteins. Our study shows that the activity of molybdoenzymes, such as sulfite oxidase, is inhibited by high concentrations of heavy metals in the cell, which will help to further the understanding of metal toxicity in E. coli.

Transfer of the Molybdenum Cofactor Synthesized by Rhodobacter capsulatus MoeA to XdhC and MobA

The molybdenum cofactor (Moco) exists in different variants in the cell and can be directly inserted into molybdoenzymes utilizing the molybdopterin (MPT) form of Moco. In bacteria such as Rhodobacter capsulatus and Escherichia coli, MPT is further modified by attachment of a GMP nucleotide, forming MPT guanine dinucleotide (MGD). In this work, we analyzed the distribution and targeting of different forms of Moco to their respective user enzymes by proteins that bind Moco and are involved in its further modification. The R. capsulatus proteins MogA, MoeA, MobA, and XdhC were purified, and their specific interactions were analyzed. Interactions between the protein pairs MogA-MoeA, MoeA-XdhC, MoeA-MobA, and XdhC-MobA were identified by surface plasmon resonance measurements. In addition, the transfer of Moco produced by the MogA-MoeA complex to XdhC was investigated. A direct competition of MobA and XdhC for Moco binding was determined. In vitro analyses showed that XdhC bound to MobA, prevented the binding of Moco to MobA, and thereby inhibited MGD biosynthesis. The data were confirmed by in vivo studies in R. capsulatus cells showing that overproduction of XdhC resulted in a 50% decrease in the activity of bis-MGD-containing Me(2)SO reductase. We propose that, in bacteria, the distribution of Moco in the cell and targeting to the respective user enzymes are accomplished by specific proteins involved in Moco binding and modification.

The Mechanism of Nucleotide-assisted Molybdenum Insertion into Molybdopterin: A NOVEL ROUTE TOWARD METAL COFACTOR ASSEMBLY

The molybdenum cofactor (Moco) is synthesized by an ancient and conserved biosynthetic pathway. In plants, the two-domain protein Cnx1 catalyzes the insertion of molybdenum into molybdopterin (MPT), a metal-free phosphorylated pyranopterin carrying an ene-dithiolate. Recently, we identified a novel biosynthetic intermediate, adenylated molybdopterin (MPT-AMP), which is synthesized by the C-terminal G domain of Cnx1. Here, we show that MPT-AMP and molybdate bind in an equimolar and cooperative way to the other N-terminal E domain (Cnx1E). Tungstate and sulfate compete for molybdate, which demonstrates the presence of an anion-binding site for molybdate. Cnx1E catalyzes the Zn(2+)-/Mg(2+)-dependent hydrolysis of MPT-AMP but only when molybdate is bound as co-substrate. MPT-AMP hydrolysis resulted in stoichiometric release of Moco that was quantitatively incorporated into plant apo-sulfite oxidase. Upon Moco formation AMP is release as second product of the reaction. When comparing MPT-AMP hydrolysis with the formation of Moco and AMP a 1.5-fold difference in reaction rates were observed. Together with the strict dependence of the reaction on molybdate the formation of adenylated molybdate as reaction intermediate in the nucleotide-assisted metal transfer reaction to molybdopterin is proposed.

Structure of the molybdopterin-bound Cnx1G domain links molybdenum and copper metabolism.

The molybdenum cofactor is part of the active site of all molybdenum-dependent enzymes, except nitrogenase. The molybdenum cofactor consists of molybdopterin, a phosphorylated pyranopterin, with an ene-dithiolate coordinating molybdenum. The same pyranopterin-based cofactor is involved in metal coordination of the homologous tungsten-containing enzymes found in archea. The molybdenum cofactor is synthesized by a highly conserved biosynthetic pathway. In plants, the multidomain protein Cnx1 catalyses the insertion of molybdenum into molybdopterin. The Cnx1 G domain (Cnx1G), whose crystal structure has been determined in its apo form, binds molybdopterin with high affinity and participates in the catalysis of molybdenum insertion. Here we present two high-resolution crystal structures of Cnx1G in complex with molybdopterin and with adenylated molybdopterin (molybdopterin-AMP), a mechanistically important intermediate. Molybdopterin-AMP is the reaction product of Cnx1G and is subsequently processed in a magnesium-dependent reaction by the amino-terminal E domain of Cnx1 to yield active molybdenum cofactor. The unexpected identification of copper bound to the molybdopterin dithiolate sulphurs in both structures, coupled with the observed copper inhibition of Cnx1G activity, provides a molecular link between molybdenum and copper metabolism.