Molybdenum cofactor biosynthesis in plants and humans

The transition element molybdenum (Mo) needs to be complexed by a special cofactor in order to gain catalytic activity. With the exception of bacterial Mo-nitrogenase, where Mo is a constituent of the FeMo-cofactor, Mo is bound to a pterin, thus forming the molybdenum cofactor Moco, which in different variants is the active compound at the catalytic site of all other Mo-containing enzymes. The biosynthesis of Moco involves the complex interaction of six proteins and is a process of four steps, which also requires reducing equivalents, iron, ATP and probably copper. After its synthesis, Moco is distributed to the apoproteins of Mo-enzymes by Moco–carrier/binding proteins that also participate in Moco-insertion into the cognate apoproteins. A deficiency in the biosynthesis of Moco has lethal consequences for the respective organisms. In humans, Moco deficiency is a severe inherited inborn error in metabolism resulting in severe neurodegeneration in newborns and causing early childhood death. Due to our better understanding of the chemistry of Moco synthesis, a first therapy has been brought to the clinic.     

Comparative Genomics and Evolution of Molybdenum Utilization

The trace element molybdenum (Mo) is the catalytic component of important enzymes involved in global nitrogen, sulfur, and carbon metabolism in both prokaryotes and eukaryotes. With the exception of nitrogenase, Mo is complexed by a pterin compound thus forming the biologically active molybdenum cofactor (Moco) at the catalytic sites of molybdoenzymes. The physiological roles and biochemical functions of many molybdoenzymes have been characterized. However, our understanding of the occurrence and evolution of Mo utilization is limited. This article focuses on recent advances in comparative genomics of Mo utilization in the three domains of life. We begin with a brief introduction of Mo transport systems, the Moco biosynthesis pathway, the role of posttranslational modifications, and enzymes that utilize Mo. Then, we proceed to recent computational and comparative genomics studies of Mo utilization, including a discussion on novel Moco-binding proteins that contain the C-terminal domain of the Moco sulfurase and that are suggested to represent a new family of molybdoenzymes. As most molybdoenzymes need additional cofactors for their catalytic activity, we also discuss interactions between Mo metabolism and other trace elements and finish with an analysis of factors that may influence evolution of Mo utilization.     

Structure of the molybdenum site in YedY, a sulfite oxidase homologue from Escherichia coli

YedY from Escherichia coli is a new member of the sulfite oxidase family of molybdenum cofactor (Moco)-containing oxidoreductases. We investigated the atomic structure of the molybdenum site in YedY by X-ray absorption spectroscopy, in comparison to human sulfite oxidase (hSO) and to a Mo(IV) model complex. The K-edge energy was indicative of Mo(V) in YedY, in agreement with X- and Q-band electron paramagnetic resonance results, whereas the hSO protein contained Mo(VI). In YedY and hSO, molybdenum is coordinated by two sulfur ligands from the molybdopterin ligand of the Moco, one thiolate sulfur of a cysteine (average Mo-S bond length of ～2.4 ?), and one (axial) oxo ligand (Mo═O, ～1.7 ?). hSO contained a second oxo group at Mo as expected, but in YedY, two species in about a 1:1 ratio were found at the active site, corresponding to an equatorial Mo-OH bond (～2.1 ?) or possibly to a shorter Mo-O(-) bond. Yet another oxygen (or nitrogen) at a ～2.6 ? distance to Mo in YedY was identified, which could originate from a water molecule in the substrate binding cavity or from an amino acid residue close to the molybdenum site, i.e., Glu104, that is replaced by a glycine in hSO, or Asn45. The addition of the poor substrate dimethyl sulfoxide to YedY left the molybdenum coordination unchanged at high pH. In contrast, we found indications that the better substrate trimethylamine N-oxide and the substrate analogue acetone were bound at a ～2.6 ? distance to the molybdenum, presumably replacing the equatorial oxygen ligand. These findings were used to interpret the recent crystal structure of YedY and bear implications for its catalytic mechanism.     

Synthesis,Redox and Spectroscopic Properties of Pterin of Molybdenum Cofactors

Pterins are bicyclic heterocycles that are found widely across Nature and are involved in a variety of biological functions. Notably, pterins are found at the core of molybdenum cofactor (Moco) containing enzymes in the molybdopterin (MPT) ligand that coordinates molybdenum and facilitates cofactor activity. Pterins are diverse and can be widely functionalized to tune their properties. Herein, the general methods of synthesis, redox and spectroscopic properties of pterin are discussed to provide more insight into pterin chemistry and their importance to biological systems.     

三(三甲硅基)环戊二烯基三羰基钼负离子的反应性

三(三甲硅基)环戊二烯基三羰基钼负离子锂盐[{η^5-(Me~3Si)~3C~5H~2}Mo(CO)~3]^-Li^+(1), 分别与MeI、phCH~2Cl及ClCH~2COOC~2H~5反应生成相应的烃基化钼衍生物[{η^5-(Me~3Si)~3C~5H~2}Mo(CO)~3R,] (R=-CH~3, 2; -CH~2ph, 3;-CH~2COOC~2H~5, 4)。1与PCl~3反应除得到预期的钼氯化物[{η^5-(Me~3Si)~3C~5H~2}Mo(CO)~3Cl](5)外, 主要得到钼磷氯化物[{η^5-(Me~3Si)~3C~5H~2}Mo(CO)~3PCl~2] 6; 1与碘反应得到钼碘化物[{η^5-(Me~3Si)~3C~5H~2}Mo(CO)~3I] 7; 1与HOAc作用后分别和CCl~4、NBS室温反应, 仅分离到脱去一个Me~3Si的钼卤化物[{η^5-(Me~3Si)~2C~5H~2}Mo(CO)~3X], (X:Cl, 8; Br, 9)。     

Structural Insights into the Incorporation of the Mo Cofactor into Sulfite Oxidase from Site‐Directed Spin Labeling

Mononuclear molybdoenzymes catalyze a broad range of redox reactions and are highly conserved in all kingdoms of life. This study addresses the question of how the Mo cofactor (Moco) is incorporated into the apo form of human sulfite oxidase (hSO) by using site‐directed spin labeling to determine intramolecular distances in the nanometer range. Comparative measurements of the holo and apo forms of hSO enabled the localization of the corresponding structural changes, which are localized to a short loop (residues 263–273) of the Moco‐containing domain. A flap‐like movement of the loop provides access to the Moco binding‐pocket in the apo form of the protein and explains the earlier studies on the in vitro reconstitution of apo‐hSO with Moco. Remarkably, the loop motif can be found in a variety of structurally similar molybdoenzymes among various organisms, thus suggesting a common mechanism of Moco incorporation.     

络合物分解法制备碳氮夹杂钼基催化剂及其催化性能

通过调变六次甲基四胺与金属钼盐的摩尔比例,以络合物分解法制备了碳氮夹杂钼基催化剂,并将其负载于氧化铝载体上．采用X射线衍射（XRD）、X射线光电子能谱（XPS）、低温氮吸附、元素分析等方法对催化剂进行了表征,发现碳氮夹杂钼基催化剂实为碳化钼（β-Mo2C）与碳氮化钼（M02CxNy）的混合物．以二苯并噻吩（DBT）的加氢脱硫反应（HDS）为探针,比较了负载型碳化钼、氮化钼及碳氮夹钼基催化剂的催化活性,发现由于夹杂催化剂中含有新的活性相Mo2CxNy。而表现出高于碳化钼和氮化钼催化剂的催化活性．     

The effect of the sixth sulfur ligand in the catalytic mechanism of periplasmic nitrate reductase

The catalytic mechanism of nitrate reduction by periplasmic nitrate reductases has been investigated using theoretical and computational means. We have found that the nitrate molecule binds to the active site with the Mo ion in the +6 oxidation state. Electron transfer to the active site occurs only in the proton‐electron transfer stage, where the Mo^V species plays an important role in catalysis. The presence of the sulfur atom in the molybdenum coordination sphere creates a pseudo‐dithiolene ligand that protects it from any direct attack from the solvent. Upon the nitrate binding there is a conformational rearrangement of this ring that allows the direct contact of the nitrate with Mo^VI ion. This rearrangement is stabilized by the conserved methionines Met141 and Met308. The reduction of nitrate into nitrite occurs in the second step of the mechanism where the two dimethyl‐dithiolene ligands have a key role in spreading the excess of negative charge near the Mo atom to make it available for the chemical reaction. The reaction involves the oxidation of the sulfur atoms and not of the molybdenum as previously suggested. The mechanism involves a molybdenum and sulfur‐based redox chemistry instead of the currently accepted redox chemistry based only on the Mo ion. The second part of the mechanism involves two protonation steps that are promoted by the presence of Mo^V species. Mo^VI intermediates might also be present in this stage depending on the availability of protons and electrons. Once the water molecule is generated only the Mo^VI species allow water molecule dissociation, and, the concomitant enzymatic turnover. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009     

Precise Quantification of Molybdate In Vitro by the FRET-Based Nanosensor ‘MolyProbe’

Molybdenum (Mo) is an essential trace element in all kingdoms of life. Mo is bioavailable as the oxyanion molybdate and gains biological activity in eukaryotes when bound to molybdopterin, forming the molybdenum cofactor. The imbalance of molybdate homeostasis results in growth deficiencies or toxic symptoms within plants, fungi and animals. Recently, fluorescence resonance energy transfer (FRET) methods have emerged, monitoring cellular and subcellular molybdate distribution dynamics using a genetically encoded molybdate-specific FRET nanosensor, named MolyProbe. Here, we show that the MolyProbe system is a fast and reliable in vitro assay for quantitative molybdate determination. We added a Strep-TagII affinity tag to the MolyProbe protein for quick and easy purification. This MolyProbe is highly stable, resistant to freezing and can be stored for several weeks at 4 °C. Furthermore, the molybdate sensitivity of the assay peaked at low nM levels. Additionally, The MolyProbe was applied in vitro for quantitative molybdate determination in cell extracts of the plant Arabidopsis thaliana, the fungus Neurospora crassa and the yeast Saccharomyces cerevisiae. Our results show the functionality of the Arabidopsis thaliana molybdate transporter MOT1.1 and indicate that FRET-based molybdate detection is an excellent tool for measuring bioavailable Mo.     

XPS Characterization of Carbon Nanotube Supported CoMo Hydrodesulfurization Catalysts

In this paper, the effect of catalytic support and sulfiding method on the chemical state of supported Co-Mo catalysts is studied by XPS. After sulfidation with in-situ method, the majority of molybdenum in CNT supported CoMo catalyst is transferred to a species with a formal chemical state Mo(Ⅳ) in MoS2 phase, and the rest to Mo(Ⅴ) which consists of Mo coordinated both to O and S, such as MoO2S2^2- and MoO3S^2-. In case of CoMo/γ-Al2O3 catalyst sulfided with in-situ method, a fraction of molybdenum is transferred to formal state Mo(Ⅳ) in the form of MoS2, but there is still a mount of unreduced Mo(VI) phase which is difficult to be sulfided. In CoMo/CNT catalyric system sulfided with ex-situ method, Mo(IV) in the form of MoS2 is detected along with a portion of unreduced Mo(VI) phase, suggesting that not all the Mo phases are reduced and sulfided by ex-situ method. As for CoMo/γ-Al2O3, a portion of molybdenum is sulfided to intermediate reduced state Mo(V) which consists of Mo coordinated both to O and S, such as MoO2S2^2- and MoO3S^2-, in addition, there is still a fraction of unreduced Mo(Ⅵ)phase. XPS analyses results suggest that CNT support facilitates the reduction and sulfidation of active species to a large extent, and that alumina support strongly interacts with active species, hereby producing a fraction of phase which resists complete sulfiding. Catalytic measurements of catalysts in the HDS of dibenzothiophene (DBT) show that CoMo/CNT catalysts are of higher HDS activity and selectivity than CoMo/γ-Al2O3 catalyst, which is in good relation with the sulfiding behavior of the corresponding catalyst.     

Synthesis of 1-(quinoxalin-2-YL) -alkane-1,2-dithiols and -alkene-1,2-dithiols of relevance to the molybdoenzymes cofactor,Moco

Syntheses are described of quinoxalines (2) and (3) carrying at C-2 a C₄-side chain, with two sulphur and two oxygen substituents appropriately placed, as model compounds for the pterin which ligands molybdenum in the oxomolybdenum enzymes cofactor, Moco.     

Physiological Importance of Molybdate Transporter Family 1 in Feeding the Molybdenum Cofactor Biosynthesis Pathway in Arabidopsis thaliana

Molybdate uptake and molybdenum cofactor (Moco) biosynthesis were investigated in detail in the last few decades. The present study critically reviews our present knowledge about eukaryotic molybdate transporters (MOT) and focuses on the model plant Arabidopsis thaliana, complementing it with new experiments, filling missing gaps, and clarifying contradictory results in the literature. Two molybdate transporters, MOT1.1 and MOT1.2, are known in Arabidopsis, but their importance for sufficient molybdate supply to Moco biosynthesis remains unclear. For a better understanding of their physiological functions in molybdate homeostasis, we studied the impact of mot1.1 and mot1.2 knock-out mutants, including a double knock-out on molybdate uptake and Moco-dependent enzyme activity, MOT localisation, and protein–protein interactions. The outcome illustrates different physiological roles for Moco biosynthesis: MOT1.1 is plasma membrane located and its function lies in the efficient absorption of molybdate from soil and its distribution throughout the plant. However, MOT1.1 is not involved in leaf cell imports of molybdate and has no interaction with proteins of the Moco biosynthesis complex. In contrast, the tonoplast-localised transporter MOT1.2 exports molybdate stored in the vacuole and makes it available for re-localisation during senescence. It also supplies the Moco biosynthesis complex with molybdate by direct interaction with molybdenum insertase Cnx1 for controlled and safe sequestering.     

Synthesis and Structure of a New Dinuclear Molybdenum(I) Compound with Cyclohexanthiolate Ligand, [Mo_2(SC_6H_(11))_2(CO)_6(CH_3CN)_2]

1 INTRODUCTION The chemistry of complexes containing low-valence molybdenum and tungsten metal atoms hasincreasingly attracted the attention from chemistsand bioinorganic chemists due to their significancefor studying metal enzymes[1～5]. Since the s…     

Spectroscopic studies of molybdenum and tungsten enzymes

Molybdenum and tungsten are the only second and third-row transition elements with a known function in living systems. Molybdenum fulfills functional roles in enzyme systems in almost all living creatures, from bacteria through plants to invertebrates and mammals, while tungsten takes the place of molybdenum in some prokaryotes, especially the hyperthermophilic archaea. The enzymes contain the metal bound by an unusual sulfur-containing cofactor. Despite possessing common structural elements, the enzymes are remarkable in the range of different chemical reactions that are catalyzed, although almost all are two-electron oxidation–reduction reactions in which an oxygen atom is transferred to or from the molybdenum. The functional roles filled by molybdenum enzymes are equally diverse; for example, they play essential roles in microbial respiration, in the uptake of nitrogen in green plants, in controlling insect eye color, and in human health. Spectroscopic studies, in particular electron paramagnetic resonance and X-ray absorption spectroscopy, have played an essential role in our understanding of the active site structures and catalytic mechanisms of the molybdenum and tungsten enzymes. This review summarizes the role spectroscopy has played in the state of our knowledge of the molybdenum and tungsten enzymes, with particular regard to structural information on the molybdenum sites.     

食物中的钼与人体健康

综述了食物中钼与人体健康之间的关系.主要包括常见食物中的钼含量,钼在人体中的代谢,钼的生物学功能以及钼对人体健康的影响等.     

氮、磷、碳化物比较研究初探

环保法规的日益严格使得研究者越来越重视新型加氢脱硫、脱氮催化剂的开发。国内外学者在对负载型Mo—Co、Mo—Ni和W—Ni等传统硫化物催化剂进行不断改进的同时,新型催化材料尤其是具有贵金属性质的过渡金属间充化合物一氮化物、碳化物和磷化物的研究也受到很大的关注。人们在探索不同的载体或者是不同的助剂对单金属间充化合物-氮化物、碳化物或磷化物催化剂活性组分的表面状态和结构以及其深度加氢脱硫脱氮性能的影响,而对同一载体负载的氮、磷、碳化物催化剂缺乏横向的比较。本研究制备了以γ-Al2O3为载体的负载型氮化钼、磷化钼和碳化钼催化剂,比较了它们的孔结构、比表面积,并初步分析了钼的质量分数为19％,氮化、磷化和碳化温度均为650℃时三类催化剂的二苯并噻吩加氢脱硫性能。     

Hydrothermal Synthesis and Structure of a Novel Binuclear Molybdenum Complex with Oxalate Ligand,(enH2){NH4[Co(en)3][Mo2O7(C2O4)]}2·2H2O

The title complex (enH2){NH4[Co(en)3][Mo2O7(C2O4)]}2·2H2O (C18H70Co2Mo4- N16O24, Mr = 1396.52) was obtained under hydrothermal conditions and its crystal structure has been determined by single-crystal X-ray diffraction. It crystallizes in the monoclinic system, space group P21/c with a = 17.8023(8), b = 7.7527(4), c = 16.9781(4)A,β= 103.878(7)°, V = 2274.8(2) A3, Dc = 2.039 g/cm3, Z = 2,μ(MoKα) = 1.878 mm-1 and F(000) = 1408. The final R = 0.0410 and Wr = 0.1070 for 4065 observed reflections with I≥2σ(I). The crystal structure is composed of bi- nuclear [Mo2O7(C2O4)]4- anions, complex [Co(en)3]2+ cations, protonated ethylenediamine cations, ammonium cations and crystal water molecules, which are held together into a three-dimensional network via hydrogen-bonding interactions. The binuclear structure of [Mo2O7(C2O4)]4- consist of one MoO4 and one MoO6 octahedra through sharing a bridging oxygen atom, where the oxalate ligand acts as a bidentate ligand coordinating to the octahedral molybdenum atom though two deprotonated corboxylate groups.     

铈量法快速测定镍钼矿硫酸介质加压浸出液中的钼

镍钼浸出液中的大量Fe^2＋和Fe^3＋,采用氢氧化钠沉淀分离,以消除铈量法在测定钼时产生的干扰。通过在钼标准中加入Ni试验证明,测定体系中存在大量Ni^2＋时,不干扰钼的测定。用草酸一硫酸联氨将Mo^6＋还原至Mo^5＋,用次甲基蓝作氧化促进剂,加快了滴定时的反应速度,终点突跃明显。拟定方法的样品加标回收率为95．0％～103．5％,相对标准偏差均〈1％。在实际测定中,方法快速准确,值得推荐。     

Synthesis and Crystal Structure ofα-Mo_4 X S_3( μ-dtp)_3(dtp)_3( X= 0 .6S + 0 .4O)

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