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钼辅因子作为氧化还原反应中的重要分子,参与硫、氮、碳的氧化还原代谢.钼辅因子主要分为两类:以铁硫簇为基础的铁钼辅因子和以亚钼蝶呤为基础的钼辅因子.钼-二-亚钼蝶呤-鸟苷二核苷钼辅因子(Mo-bis-MGD)是蝶呤型钼辅因子的重要成员之一,是硝酸盐还原酶的重要辅因子.膜结合硝酸盐还原酶介导的硝酸盐还原为细菌提供了氮源和能... 相似文献
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植物中钼的吸收转运及钼辅因子与钼酶的研究进展 总被引:1,自引:0,他引:1
钼是植物生长发育所必需的微量元素,只有和蛋白质或者蝶呤结合形成钼辅因子才能产生生物活性。自然界存在2种钼辅因子:以铁硫簇为基础的铁钼辅因子(Fe Moco)和以钼蝶呤为基础的钼辅因子(MPT/Moco)。植物对钼的吸收有2种转运蛋白系统,一种是专一性转运蛋白,如MOTl和MOT2;另一种是共转运蛋白,如磷酸盐转运蛋白(PHT)和硫酸盐转运蛋白(SULTR)。最近研究发现一种钼酶——线粒体氨肟还原蛋白(m ARC)。本文综述了近年来植物体内钼的吸收与转运机制、钼辅因子的合成过程以及钼酶的研究进展,并提出了今后的重点研究方向。 相似文献
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以UW45抽提液的DEAE-纤维素柱层析的0.15M NaCl或0.25M NaCl洗出液与Smith法或Shah法制备的铁铝辅因子重组,则0.25 M NaCl洗出液的重组对乙炔还原的活性远较0.15 M NaGl的为高。0.15 M NaGl的洗出液较0.25 M NaCl洗出液的组分明显不纯。不全钼铁蛋白与铁钼辅因子和铁蛋白重组后能还原基质氰化钾,但对分子氮或迭氮化钠的还原却较微弱甚至不还原。铁钼辅因子按Smith和Shah法制备,其分子量范围分别为低于1000D和接近1500D。由于Smith和Shah法两种铁钼辅因子还原乙炔和氰化钾的比活不同,电泳图谱有差异、分子量又有大小,因此这两种铁钼辅因子的分子结构可能不尽相同。 相似文献
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棕色固氮菌固氮酶钼铁蛋白结晶,经酒石酸解离后得到一个含钢铁小分子组分,与棕色固氮菌突变株uw_(45)无细胞提取液的重组比活为6.8nM Mo natom~(-1) min~(-1)。它是由二种物质组成的混合物,其分子量分别为2100和1850道尔顿,分子量为2100道尔顿的成分含钼铁。酒石酸处理后的沉淀,再用N—甲基甲酰胺抽提得到的含钼铁组分具有恢复突变株uw_(45)乙炔还原活性的能力。经纸层析鉴定与用Shah法制备的铁钼辅因子相类似。由于Shah和Smith法制备的两种铁钼辅因子还原乙炔和氰化钾的比活不同,而且分子量也有大小,说明这两种铁钼辅因子结构可能不尽相同。 相似文献
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固氮酶由两种铁硫蛋白(钼铁蛋白和铁蛋白)组成。由还原剂提供电子经铁(Fe)蛋白传递给钼铁(MoFe)蛋白,在MoFe蛋白的活性中心部位进行N_2、C_2H_2等多种底物的还原[10,11,20]。MoFe蛋白中的Mo、Fe原子和酸不稳定性硫原子(S~*)组成2个M簇(FeM-oco)、3—4个P簇(P-cluster)及1—2个S(2Fe)簇。在底物还原过程中,这些原子簇都可能参与电子的传递。铁钼辅因子(FeMoco)已被认为是络合和还原底物的重要部位。因此,要阐明MoFe蛋白的作用机理就得研究FeMoco的结构和功 相似文献
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This work provides the first extensive study of the redox reactivity of the pyranopterin system that is a component of the catalytic site of all molybdenum and tungsten enzymes possessing molybdopterin. The pyranopterin system possesses certain characteristics typical of tetrahydropterins, such as a reduced pyrazine ring; however, it behaves as a dihydropterin in redox reactions with oxidants. Titrations using ferricyanide and dichloroindophenol (DCIP) prove a 2e–/2H+ stoichiometry for pyranopterin oxidations. Oxidations of pyranopterin by Fe(CN)6
3– or DCIP are slower than tetrahydropterin oxidation under a variety of conditions, but are considerably faster than observed for oxidations of dihydropterin. The rate of pyranopterin oxidation by DCIP was studied in a variety of media. In aqueous buffered solution the pyranopterin oxidation rate has minimal pH dependence, whereas the rate of tetrahydropterin oxidation decreases 100-fold over the pH range 7.4–8.5. Although pyranopterin reacts as a dihydropterin with oxidants, it resists further reduction to a tetrahydropterin. No reduction was achieved by catalytic hydrogenation, even after several days. The reducing ability of the commonly used biological reductants dithionite and methyl viologen radical cation was investigated, but experiments showed no evidence of pyranopterin reduction by any of these reducing agents. This study illustrates the dual personalities of pyranopterin and underscores the unique place that the pyranopterin system holds in the spectrum of pterin redox reactions. The work presented here has important implications for understanding the biosynthesis and reaction chemistry of the pyranopterin cofactor in molybdenum and tungsten enzymes.Abbreviations DCIP
dichloroindophenol
- H4DMP
6,7-dimethyltetrahydropterin
- MV+
methyl viologen radical cation 相似文献
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Addition of trifluoroacetic acid to syn-[MoO(μ-N-o-tol)(S2CNEt2)]2 in chloroform affords tetranuclear [{Mo2O(S2CNEt2)(η1-O2CCF3)(μ-N-o-tol)2}2(μ-O)(μ-O2CCF3)2] which has been crystallographically characterised. It consists of four molybdenum(V) centres linked via bridging imido, trifluoroacetate and oxo ligands and results from replacement of a dithiocarbamate by two trifluoroacetate ligands. 相似文献
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Kuan-I Chen Alastair G. McEwan Paul V. Bernhardt 《Journal of biological inorganic chemistry》2009,14(3):409-419
Electrochemically driven catalysis of the bacterial enzyme dimethyl sulfoxide (DMSO) reductase (Rhodobacter capsulatus) has been studied using the macrocyclic complex (trans-6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane-6,13-diamine)cobalt(III) as a mediator. In the presence of both DMSO and
DMSO reductase, the normal transient CoIII/II voltammetric response of the complex is transformed into an amplified and sigmoidal (steady-state) waveform characteristic
of a catalytic EC′ mechanism. At low concentrations of DMSO (approximately K
M) or high mediator concentrations (more than the concentration of DMSO reductase), the steady-state character of the voltammetric
response disappears and is replaced by more complicated waveforms that are a convolution of transient and steady-state behavior
as different steps within the catalytic cycle become rate limiting. Through digital simulation of cyclic voltammetry performed
under conditions where the sweep rate, DMSO concentration, DMSO reductase concentration and mediator concentration were varied
systematically, we were able to model all voltammograms with a single set of rate and equilibrium constants which provide
new insights into the kinetics of the DMSO reductase catalytic mechanism that have hitherto been inaccessible from steady
state or stopped flow kinetic studies.
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Paul V. BernhardtEmail: |
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Marie-Anne Pilette 《Inorganica chimica acta》2010,363(15):4253-4261
Reaction at pH = 2.3 of the [Mo2O2S2(OH2)6]2+ aqua cation with the tetravacant ion [β-B-HAs2W8O31]7− leads to the formation of a red solid from which three mixed salts have been obtained as single crystals and characterized by X-ray diffraction analysis. Three mixed salts K-5a, RbNa-5b, DMACs-5c exhibit a similar molecular arrangement consisting in three {β-HAs2W9O34} subunits mutually linked by three {Mo2O2S2} groups. The triangular arrangement delimits a large open-cavity, lined on the periphery by three outer {As-OH} groups and closed at the bottom by a small hexagonal pocket formed by six terminal oxygen atoms. The central hexagonal cavity is filled either by a potassium, a rubidium or a cesium cation. The outer {As-OH} groups are pointed towards two directions labelled up and down, respectively. In K-6a the three {As-OH} bonds are in up configuration leading to the {up, up, up} isomer. The structure of RbNa-5b is rather consistent with the superposition of the two {up, up, up} and {down, up, up} isomers disordered over the same crystallographic site, while only the {down, up, up} isomer is present in DMACs-5c. In solution, 183W NMR characterization of 6a as sodium salt results in a complicated spectrum consistent with the simultaneous presence of the four isomers, {up, up, up}, {down, up, up}, {down, down, up} and {down, down, down}, respectively. 5a reacts with three equivalents of iodine to give CsNa-6 isolated as single crystals. In 6, four β-{AsW9O33} moieties are located at the corner of a super tetrahedron and are mutually connected by six {Mo2O2S2} linkers. The three outer {As-OH} groups can be selectively removed by iodine, this oxidation reaction consisting in fact in a deprotecting process permitting the extension of the arrangement from triangular to tetrahedral. 相似文献
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Seminalplasmin, an antimicrobial protein from bovine seminal plasma, inhibited peptidoglycan synthesis in Escherichia coli in a concentration-dependent manner. The inhibition of peptidoglycan synthesis appears to be a cause rather than a consequence of growth inhibition as it was observed soon after the addition of the antibiotic even in E. coli cells whose growth was totally inhibited by chloramphenicol. 相似文献
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Identification and Biochemical Characterization of Molybdenum Cofactor-binding Proteins from Arabidopsis thaliana 总被引:1,自引:0,他引:1
Tobias Kruse Christian Gehl Mirco Geisler Markus Lehrke Phillip Ringel Stephan Hallier Robert H?nsch Ralf R. Mendel 《The Journal of biological chemistry》2010,285(9):6623-6635
The molybdenum cofactor (Moco) forms part of the catalytic center in all eukaryotic molybdenum enzymes and is synthesized in a highly conserved pathway. Among eukaryotes, very little is known about the processes taking place subsequent to Moco biosynthesis, i.e. Moco transfer, allocation, and insertion into molybdenum enzymes. In the model plant Arabidopsis thaliana, we identified a novel protein family consisting of nine members that after recombinant expression are able to bind Moco with KD values in the low micromolar range and are therefore named Moco-binding proteins (MoBP). For two of the nine proteins atomic structures are available in the Protein Data Bank. Surprisingly, both crystal structures lack electron density for the C terminus, which may indicate a high flexibility of this part of the protein. C-terminal truncated MoBPs showed significantly decreased Moco binding stoichiometries. Experiments where the MoBP C termini were exchanged among MoBPs converted a weak Moco-binding MoBP into a strong binding MoBP, thus indicating that the MoBP C terminus, which is encoded by a separate exon, is involved in Moco binding. MoBPs were able to enhance Moco transfer to apo-nitrate reductase in the Moco-free Neurospora crassa mutant nit-1. Furthermore, we show that the MoBPs are localized in the cytosol and undergo protein-protein contact with both the Moco donor protein Cnx1 and the Moco acceptor protein nitrate reductase under in vivo conditions, thus indicating for the MoBPs a function in Arabidopsis cellular Moco distribution. 相似文献
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The oxygen atom transfer reactivity of Tp( *)MoO(2)(SPh) (1) (where Tp( *)=hydrotris-(3,5-dimethylpyrazol-1-yl)borate) with trimethyl phosphine (PMe(3)) has been investigated. The reaction proceed through a diamagnetic phosphoryl intermediate complex, Tp( *)MoO(SPh)(OPMe(3)) (2), which has been isolated and characterized by IR, NMR, UV-visible spectroscopy, and mass spectrometry. The molecular structure of 2 has been determined by X-ray crystallography. The complex crystallizes in monoclinic (P2(1)/n) space group, a=19.81 (1)A, b=11.1 (4)A, c=18.416 (5)A, beta=121.2 (3) degrees , V=3463.8 (25)A(3) with Z=4. In acetonitrile, complex 2 exchanges its phosphoryl ligand with a solvent molecule resulting in Tp( *)MoO(SPh)(MeCN) (3), which has been isolated and also characterized spectroscopically and by X-ray crystallography. Compound 3 crystallizes in triclinic (P1 ) space group, a=10.159 (6)A, b=18.563 (5)A, c=7.986 (3)A, alpha=96.22 (3) degrees , beta=121.2 (3) degrees , gamma=84.64 (3) degrees , V=1452.4 (11)A(3) with Z=2. The electronic structures of the complexes have been investigated by density functional theory and the redox chemistry has been investigated by cyclic and differential pulse voltammetry. In acetonitrile, complex 2 spontaneously transforms to complex, 3 at a rate of 5.6x10(-4)s(-1). 相似文献
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Ceyhan Kayran 《Inorganica chimica acta》2004,357(1):143-148
Reported is a combined time-resolved optical (TRO) and infrared (TRIR) spectroscopic investigation of the flash photolysis of Mo(CO)6 in cyclohexane solution. TRIR studies using 308 nm excitation led to transient bleaching of the strong νCO band at 1987 cm−1 of Mo(CO)6 and appearance of new bands at 1931 and 1964 cm−1 attributed to Mo(CO)5(Sol). Using a high pressure/variable temperature flow cell, the kinetics of back reaction with CO (kCO) to regenerate the hexacarbonyl was studied over the PCO range 1-20 atm and at five temperatures. These data gave kCO=4.6±0.2×106 M−1 s−1 (298 K) and the activation parameters kJ/mol and J mol−1 K−1 from which an interchange mechanism was proposed. The analogous species seen in the TRO experiment displayed a transient absorbance at 420 nm and analogous kinetics properties although at lower PCO self-trapping with Mo(CO)6 (to give Mo2(CO)11) is a competitive process. The Mo(CO)5(Sol) transient could also be trapped by nPrBr (kRBr=5.3±0.7×107 M−1 s−1). 相似文献
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Nicole L. Creevey Alastair G. McEwan Paul V. Bernhardt 《Journal of biological inorganic chemistry》2008,13(8):1231-1238
Dimethyl sulfide dehydrogenase isolated from the photosynthetic bacterium Rhodovulum sulfidophilum is a heterotrimeric enzyme containing a molybdenum cofactor at its catalytic site, as well as five iron–sulfur clusters and
a heme b cofactor. It oxidizes dimethyl sulfide (DMS) to dimethyl sulfoxide in its native role and transfers electrons to the photochemical
reaction center. There is genetic evidence that cytochrome c
2 mediates this process, and the steady state kinetics experiments reported here demonstrated that cytochrome c
2 accepts electrons from DMS dehydrogenase. At saturating concentrations of both substrate (DMS) and cosubstrate (cytochrome
c
2), Michaelis constants, K
M,DMS and K
M,cyt of 53 and 21 μM, respectively, were determined at pH 8. Further kinetic analysis revealed a “ping-pong” enzyme reaction mechanism
for DMS dehydrogenase with its two reactants. Direct cyclic voltammetry of cytochrome c
2 immobilized within a polymer film cast on a glassy carbon electrode revealed a reversible FeIII/II couple at +328 mV versus the normal hydrogen electrode at pH 8. The FeIII/II redox potential exhibited only minor pH dependence. In the presence of DMS dehydrogenase and DMS, the peak-shaped voltammogram
of cytochrome c
2 is transformed into a sigmoidal curve consistent with a steady-state (catalytic) reaction. The cytochrome c
2 effectively mediates electron transfer between the electrode and DMS dehydrogenase during turnover and a significantly lower
apparent electrochemical Michaelis constant of 13(±1) μM was obtained. The pH optimum for catalytic DMS oxidation by DMS dehydrogenase with cytochrome c
2 as the electron acceptor was found to be approximately 8.3. 相似文献