Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.7.1.2 (nitrate reductase)
 3,861 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A soluble cytochrome b(558) from the purple phototropic bacterium Ectothiorhodospira vacuolata was completely sequenced by a combination of automated Edman degradation and mass spectrometry. The protein, with a measured mass of 10,094.7 Da, contains 90 residues and binds a single protoheme. Unexpectedly, the sequence shows homology to eukaryotic cytochromes b(5). As no prokaryotic homologue had been reported so far, we developed a protocol for the expression, purification, and crystallization of recombinant cytochrome b(558). The structure was solved by molecular replacement to a resolution of 1.65 A. It shows that cytochrome b(558) is indeed the first bacterial cytochrome b(5) to be characterized and differs from its eukaryotic counterparts by the presence of a disulfide bridge and a four-residue insertion in front of the sixth ligand (histidine). Eukaryotes contain a variety of b(5) homologues, including soluble and membrane-bound multifunctional proteins as well as multidomain enzymes such as sulfite oxidase, fatty-acid desaturase, nitrate reductase, and lactate dehydrogenase. A search of the Mycobacterium tuberculosis genome showed that a previously unidentified gene encodes a fatty-acid desaturase with an N-terminal b(5) domain. Thus, it may provide another example of a bacterial b(5) homologue.
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PMID:Structure and characterization of Ectothiorhodospira vacuolata cytochrome b(558), a prokaryotic homologue of cytochrome b(5). 1058 39

The active sites of the xanthine oxidase and sulfite oxidase enzyme families contain one pterin-dithiolene cofactor ligand bound to a molybdenum atom. Consequently, monodithiolene molybdenum complexes have been sought by exploratory synthesis for structural and reactivity studies. Reaction of [MoO(S(2)C(2)Me(2))(2)](1-) or [MoO(bdt)(2)](1-) with PhSeCl results in removal of one dithiolate ligand and formation of [MoOCl(2)(S(2)C(2)Me(2))](1-) (1) or [MoOCl(2)(bdt)](1-) (2), which undergoes ligand substitution reactions to form other monodithiolene complexes [MoO(2-AdS)(2)(S(2)C(2)Me(2))](1-) (3), [MoO(SR)(2)(bdt)](1-) (R = 2-Ad (4), 2,4,6-Pr(i)(3)C(6)H(2) (5)), and [MoOCl(SC(6)H(2)-2,4,6-Pr(i)(3))(bdt)](1-) (6) (Ad = 2-adamantyl, bdt = benzene-1,2-dithiolate). These complexes have square pyramidal structures with apical oxo ligands, exhibit rhombic EPR spectra, and 3-5 are electrochemically reducible to Mo(IV)O species. Complexes 1-6 constitute the first examples of five-coordinate monodithiolene Mo(V)O complexes; 6 approaches the proposed structure of the high-pH form of sulfite oxidase. Treatment of [MoO(2)(OSiPh(3))(2)] with Li(2)(bdt) in THF affords [MoO(2)(OSiPh(3))(bdt)](1-) (8). Reaction of 8 with 2,4,6-Pr(i)(3)C(6)H(2)SH in acetonitrile gives [MoO(2)(SC(6)H(2)-2,4,6-Pr(i)(3))(bdt)](1-) (9, 55%). Complexes 8 and 9 are square pyramidal with apical and basal oxo ligands. With one dithiolene and one thiolate ligand of a square pyramidal Mo(VI)O(2)S(3) coordination unit, 9 closely resembles the oxidized sites in sulfite oxidase and assimilatory nitrate reductase as deduced from crystallography (sulfite oxidase) and Mo EXAFS. The complex is the first structural analogue of the active sites in fully oxidized members of the sulfite oxidase family. This work provides a starting point for the development of both structural and reactivity analogues of members of this family.
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PMID:Monodithiolene molybdenum(V, VI) complexes: a structural analogue of the oxidized active site of the sulfite oxidase enzyme family. 1151 83

Nitrate reductase (NR; EC 1.6.6.1-3) catalyzes NAD(P)H reduction of nitrate to nitrite. NR serves plants, algae, and fungi as a central point for integration of metabolism by governing flux of reduced nitrogen by several regulatory mechanisms. The NR monomer is composed of a ~100-kD polypeptide and one each of FAD, heme-iron, and molybdenum-molybdopterin (Mo-MPT). NR has eight sequence segments: (a) N-terminal "acidic" region; (b) Mo-MPT domain with nitrate-reducing active site; (c) interface domain; (d) Hinge 1 containing serine phosphorylated in reversible activity regulation with inhibition by 14-3-3 binding protein; (e) cytochrome b domain; (f) Hinge 2; (g) FAD domain; and (h) NAD(P)H domain. The cytochrome b reductase fragment contains the active site where NAD(P)H transfers electrons to FAD. A complete three-dimensional dimeric NR structure model was built from structures of sulfite oxidase and cytochrome b reductase. Key active site residues have been investigated. NR structure, function, and regulation are now becoming understood.
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PMID:NITRATE REDUCTASE STRUCTURE, FUNCTION AND REGULATION: Bridging the Gap between Biochemistry and Physiology. 1501 11

Molybdenum and tungsten are second- and third-row transition elements, respectively, which are found in a mononuclear form in the active site of a diverse group of enzymes that generally catalyze oxygen atom transfer reactions. Mononuclear Mo-containing enzymes have been classified into three families: xanthine oxidase, DMSO reductase, and sulfite oxidase. The proteins of the DMSO reductase family present the widest diversity of properties among its members and our knowledge about this family was greatly broadened by the study of the enzymes nitrate reductase and formate dehydrogenase, obtained from different sources. We discuss in this review the information of the better characterized examples of these two types of Mo enzymes and W enzymes closely related to the members of the DMSO reductase family. We briefly summarize, also, the few cases reported so far for enzymes that can function either with Mo or W at their active site.
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PMID:Mo and W bis-MGD enzymes: nitrate reductases and formate dehydrogenases. 1531 35

The molybdenum cofactor (Moco) forms the active site of all eukaryotic molybdenum (Mo) enzymes. Moco consists of molybdenum covalently bound to two sulfur atoms of a unique tricyclic pterin moiety referred to as molybdopterin. Moco is synthesized from GTP by an ancient and conserved biosynthetic pathway that can be divided into four steps involving the biosynthetic intermediates cyclic pyranopterin monophosphate, molybdopterin, and adenylated molybdopterin. In a fifth step, sulfuration or bond formation between Mo and a protein cysteine result in two different catalytic Mo centers. There are four Mo enzymes in plants: (1) nitrate reductase catalyzes the first and rate-limiting step in nitrate assimilation and is structurally similar to the recently identified, (2) peroxisomal sulfite oxidase that detoxifies excessive sulfite. (3) Aldehyde oxidase catalyzes the last step of abscisic acid biosynthesis, and (4) xanthine dehydrogenase is essential for purine degradation and stress response.
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PMID:Molybdenum cofactor biosynthesis and molybdenum enzymes. 1666 76

The transition element molybdenum (Mo) is of essential importance for (nearly) all biological systems as it is required by enzymes catalyzing diverse key reactions in the global carbon, sulfur and nitrogen metabolism. The metal itself is biologically inactive unless it is complexed by a special cofactor. With the exception of bacterial nitrogenase, where Mo is a constituent of the FeMo-cofactor, Mo is bound to a pterin, thus forming the molybdenum cofactor (Moco) which is the active compound at the catalytic site of all other Mo-enzymes. In eukaryotes, the most prominent Mo-enzymes are (1) sulfite oxidase, which catalyzes the final step in the degradation of sulfur-containing amino acids and is involved in detoxifying excess sulfite, (2) xanthine dehydrogenase, which is involved in purine catabolism and reactive oxygen production, (3) aldehyde oxidase, which oxidizes a variety of aldehydes and is essential for the biosynthesis of the phytohormone abscisic acid, and in autotrophic organisms also (4) nitrate reductase, which catalyzes the key step in inorganic nitrogen assimilation. All Mo-enzymes, except plant sulfite oxidase, need at least one more redox active center, many of them involving iron in electron transfer. The biosynthesis of Moco involves the complex interaction of six proteins and is a process of four steps, which also includes iron as well as copper in an indispensable way. Moco as released after synthesis is likely to be distributed to the apoproteins of Mo-enzymes by putative Moco-carrier proteins. Xanthine dehydrogenase and aldehyde oxidase, but not sulfite oxidase and nitrate reductase, require the post-translational sulfuration of their Mo-site for becoming active. This final maturation step is catalyzed by a Moco-sulfurase enzyme, which mobilizes sulfur from l-cysteine in a pyridoxal phosphate-dependent manner as typical for cysteine desulfurases.
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PMID:Cell biology of molybdenum. 1678 86

The transition element molybdenum (Mo) is an essential micronutrient that is needed as catalytically active metal during enzyme catalysis. In humans four enzymes depend on Mo: sulfite oxidase, xanthine oxidoreductase, aldehyde oxidase, and mitochondrial amidoxime reductase. In addition to these enzymes, plants harbor a fifth Mo-enzyme namely nitrate reductase. To gain biological activity and fulfill its function in enzymes, Mo has to be complexed by a pterin compound thus forming the molybdenum cofactor. This article will review the way that Mo takes from uptake into the cell, via formation of the molybdenum cofactor and its storage, up to the final insertion of the molybdenum cofactor into apometalloenzymes.
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PMID:Cell biology of molybdenum. 1962 4

The molybdenum cofactor (Moco) is a prosthetic group required by a number of enzymes, such as nitrate reductase, sulfite oxidase, xanthine dehydrogenase, and aldehyde oxidase. Its biosynthesis in eukaryotes can be divided into four steps, of which the last three are proposed to occur in the cytosol. Here, we report that the mitochondrial ABC transporter ATM3, previously implicated in the maturation of extramitochondrial iron-sulfur proteins, has a crucial role also in Moco biosynthesis. In ATM3 insertion mutants of Arabidopsis thaliana, the activities of nitrate reductase and sulfite oxidase were decreased to approximately 50%, whereas the activities of xanthine dehydrogenase and aldehyde oxidase, whose activities also depend on iron-sulfur clusters, were virtually undetectable. Moreover, atm3 mutants accumulated cyclic pyranopterin monophosphate, the first intermediate of Moco biosynthesis, but showed decreased amounts of Moco. Specific antibodies against the Moco biosynthesis proteins CNX2 and CNX3 showed that the first step of Moco biosynthesis is localized in the mitochondrial matrix. Together with the observation that cyclic pyranopterin monophosphate accumulated in purified mitochondria, particularly in atm3 mutants, our data suggest that mitochondria and the ABC transporter ATM3 have a novel role in the biosynthesis of Moco.
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PMID:A novel role for Arabidopsis mitochondrial ABC transporter ATM3 in molybdenum cofactor biosynthesis. 2016 45

Almost all living organisms need to obtain molybdenum from the external medium to achieve essential processes for life. Activity of important enzymes such as sulfite oxidase, aldehyde oxidase, xanthine dehydrogenase, and nitrate reductase is strictly dependent on the presence of Mo in its active site. Cells take up Mo in the form of the oxianion molybdate, but the molecular nature of the transporters is still not well known in eukaryotes. MOT1 is the first molybdate transporter identified in plant-type eukaryotic organisms, but it is absent in animal genomes. Here we report a molybdate transporter different from the MOT1 family, encoded by the Chlamydomonas reinhardtii gene MoT2, that is also present in animals including humans. The knockdown of CrMoT2 transcription leads to the deficiency of molybdate uptake activity in Chlamydomonas. In addition, heterologous expression in Saccharomyces cerevisiae of MoT2 genes from Chlamydomonas and humans support the functionality of both proteins as molybdate transporters. Characterization of CrMOT2 and HsMOT2 activities showed an apparent Km of about 550 nM that, though higher than the Km reported for MOT1, still corresponds to high affinity systems. CrMoT2 transcription is activated when extracellular molybdate concentration is low but in contrast to MoT1 is not activated by nitrate. Analysis of protein databases revealed the presence of four motifs present in all the proteins with high similarity to MOT2, that label a previously undescribed family of proteins probably related to molybdate transport. Our results open the way toward the understanding of molybdate transport as part of molybdenum homeostasis and Moco biosynthesis in animals.
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PMID:Algae and humans share a molybdate transporter. 2146 89

The transition element molybdenum (Mo) is of essential importance for (nearly) all biological systems as it is required by enzymes catalyzing important reactions within the cell. The metal itself is biologically inactive unless it is complexed by a special cofactor. With the exception of bacterial nitrogenase, where Mo is a constituent of the FeMo-cofactor, Mo is bound to a pterin, thus forming the molybdenum cofactor (Moco) which is the active compound at the catalytic site of all other Mo-enzymes. In plants, the most prominent Mo-enzymes are nitrate reductase, sulfite oxidase, xanthine dehydrogenase, aldehyde oxidase, and the mitochondrial amidoxime reductase. The biosynthesis of Moco involves the complex interaction of six proteins and is a process of four steps, which also includes iron as well as copper in an indispensable way. 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. Xanthine dehydrogenase and aldehyde oxidase, but not the other Mo-enzymes, require a final step of posttranslational activation of their catalytic Mo-center for becoming active.
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PMID:Cell biology of molybdenum in plants. 2166 May 47


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