Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:1.12.7.2 (hydrogenase)
3,522 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The mechanism for U(VI) reduction by Desulfovibrio vulgaris (Hildenborough) was investigated. The H2-dependent U(VI) reductase activity in the soluble fraction of the cells was lost when the soluble fraction was passed over a cationic exchange column which extracted cytochrome c3. Addition of cytochrome c3 back to the soluble fraction that had been passed over the cationic exchange column restored the U(VI)-reducing capacity. Reduced cytochrome c3 was oxidized by U(VI), as was a c-type cytochrome(s) in whole-cell suspensions. When cytochrome c3 was combined with hydrogenase, its physiological electron donor, U(VI) was reduced in the presence of H2. Hydrogenase alone could not reduce U(VI). Rapid U(VI) reduction was followed by a subsequent slow precipitation of the U(IV) mineral uraninite. Cytochrome c3 reduced U(VI) in a uranium-contaminated surface water and groundwater. Cytochrome c3 provides the first enzyme model for the reduction and biomineralization of uranium in sedimentary environments. Furthermore, the finding that cytochrome c3 can catalyze the reductive precipitation of uranium may aid in the development of fixed-enzyme reactors and/or organisms with enhanced U(VI)-reducing capacity for the bioremediation of uranium-contaminated waters and waste streams.
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PMID:Reduction of uranium by cytochrome c3 of Desulfovibrio vulgaris. 828 65

H2-forming N5,N10-methylenetetrahydromethanopterin dehydrogenase is a novel hydrogenase found in most methanogenic archaea. It catalyzes the reversible conversion of N5,N10-methylenetetrahydromethanopterin (CH2 = H4MPT) to N5,N10-methenyltetrahydromethanopterin (CH identical to H4MPT+) and dihydrogen; CH2 = H4MPT + H+<-->CH identical to H4MPT(+) + H2; delta G degrees ' = + 5 kJ/mol. In the following investigation, the formation of H2, HD and D2 was studied in experiments in which either the methylene group of CH2 = H4MPT or water were deuterium labelled. In the case of CD2 = H4MPT and H2O, the dihydrogen formed immediately after the start of the reaction was composed of approximately 50% HD and 50% of H2 at all pH tested. In the case of CH2 = H4MPT and D2O, the dihydrogen generated was composed of approximately 50% HD and 50% D2 at pD 5.7 and of approximately 85% HD and 15% D2 at pD 7.0. Evidence is presented that the enzyme catalyzes a CH identical to H4MPT(+)-dependent isotopic exchange between HD and H2O and between HD and D2O, yielding H2 and D2, respectively. A catalytic mechanism aimed to explain these findings is discussed.
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PMID:H2-forming N5,N10-methylenetetrahydromethanopterin dehydrogenase from Methanobacterium thermoautotrophicum. Studies of the catalytic mechanism of H2 formation using hydrogen isotopes. 838 41

Redox intermediates of D. desulfuricans ATCC 27774 [NiFe] hydrogenase were generated under dihydrogen. Detailed redox titrations, coupled to EPR measurements, give access to the mid-point redox potentials of the iron-sulfur centers and of the Nickel-B signal that represents the ready form of the enzyme. The interaction between the dihydrogen molecule and the nickel centre was probed by the observation of an isotopic effect on the EPR signals detected in turnover conditions, by comparison of the H2O/H2 and D2O/D2-reacted samples.
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PMID:Characterization of D. desulfuricans (ATCC 27774) [NiFe] hydrogenase EPR and redox properties of the native and the dihydrogen reacted states. 839 80

In the presence of carbon monoxide, the photosynthetic bacterium Rhodospirillum rubrum induces expression of proteins which allow the organism to metabolize carbon monoxide in the net reaction CO + H2O --> CO2 + H2. These proteins include the enzymes carbon monoxide dehydrogenase (CODH) and a CO-tolerant hydrogenase. In this paper, we present the complete amino acid sequence for the large subunit of this hydrogenase and describe the properties of the crude enzyme in relation to other known hydrogenases. The amino acid sequence deduced from the CO-induced hydrogenase large-subunit gene (cooH) shows significant similarity to large subunits of other Ni-Fe hydrogenases. The closest similarity is with HycE (58% similarity and 37% identity) from Escherichia coli, which is the large subunit of an Ni-Fe hydrogenase (isoenzyme 3). The properties of the CO-induced hydrogenase are unique. It is exceptionally resistant to inhibition by carbon monoxide. It also exhibits a very high ratio of H2 evolution to H2 uptake activity compared with other known hydrogenases. The CO-induced hydrogenase is tightly membrane bound, and its inhibition by nonionic detergents is described. Finally, the presence of nickel in the hydrogenase is addressed. Analysis of wild-type R. rubrum grown on nickel-depleted medium indicates a requirement for nickel for hydrogenase activity. However, analysis of strain UR294 (cooC insertion mutant defective in nickel insertion into CODH) shows that independent nickel insertion mechanisms are utilized by hydrogenase and CODH. CooH lacks the C-terminal peptide that is found in other Ni-Fe hydrogenases; in other systems, this peptide is cleaved during Ni processing.
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PMID:Characterization of the CO-induced, CO-tolerant hydrogenase from Rhodospirillum rubrum and the gene encoding the large subunit of the enzyme. 862 76

Azotobacter vinelandii hydrogenase was purified aerobically with a 35% yield. The purified enzyme catalyzed H2 oxidation at much greater velocity than H2 evolution. There was a large difference in activation energy for the two reactions. EA was 10 kcal/mol for H2 oxidation and 22 kcal/mol for evolution. This difference in activation energies between the two reactions means that the ratio of oxidation velocity to evolution velocity drops from 70 at 33 degrees C to 8 at 48 degrees C. With D2 and H2O as substrates, both membranes and purified enzyme produced only H2 and no HD in the isotope exchange reaction. The velocity of isotope exchange was equal to the velocity of H2 evolution from reduced methyl viologen, indicating that the two reactions share the same rate-limiting step. D2 and H2 inhibited H2 evolution, but D2 did not inhibit isotope exchange. We conclude that H2 and D2 do not inhibit H2 evolution by competing with H+ for the active site of the reduced enzyme. The Km for D2 in isotope exchange is 40-times greater than its Km in D2 oxidation. The difference in Km cannot be accounted for by differences in kcat. We propose that redox environment regulates hydrogenase's affinity for D2 (and likely H2 as well).
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PMID:Comparison of isotope exchange, H2 evolution, and H2 oxidation activities of Azotobacter vinelandii hydrogenase. 864 37

Methanol:5-hydroxybenzimidazolylcobamide methyltransferase (MT1) is the first of two enzymes involved in the transmethylation reaction from methanol to 2-mercaptoethanesulfonic acid in Methanosarcina barkeri. MT1 only binds the methyl group of methanol when the cobalt atom of its corrinoid prosthetic groups is present in the highly reduced Co(I) state. Formation of this redox state requires H2, hydrogenase, methyltransferase activation protein, and ATP. Optical and electron paramagnetic resonance spectroscopy studies were employed to determine the oxidation states and coordinating ligands of the corrinoids of MT1 during the activation process. Purified MT1 contained 1.7 corrinoids per enzyme with cobalt in the fully oxidized Co(III) state. Water and N-3 of the 5-hydroxybenzimidazolyl base served as the upper and lower ligands, respectively. Reduction to the Co(II) level was accomplished by H2 and hydrogenase. The cob(II)amide of MT1 had the base coordinated at this stage. Subsequent addition of methyltransferase activation protein and ATP resulted in the formation of base-uncoordinated Co(II) MT1. The activation mechanism is discussed within the context of a proposed model and compared to those described for other corrinoid-containing methyl group transferring proteins.
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PMID:Activation mechanism of methanol:5-hydroxybenzimidazolylcobamide methyltransferase from Methanosarcina barkeri. 879 95

In the photosynthetic bacterium Rhodospirillum rubrum, the presence of carbon monoxide (CO) induces expression of several proteins. These include carbon monoxide dehydrogenase (CODH) and a CO-tolerant hydrogenase. Together these enzymes catalyze the following conversion: CO + H2O --> CO2 + H2. This system enables R. rubrum to grow in the dark on CO as the sole energy source. Expression of this system has been shown previously to be regulated at the transcriptional level by CO. We have now identified the remainder of the CO-regulated genes encoded in a contiguous region of the R. rubrum genome. These genes, cooMKLXU, apparently encode proteins related to the function of the CO-induced hydrogenase. As seen before with the gene for the large subunit of the CO-induced hydrogenase (cooH), most of the proteins predicted by these additional genes show significant sequence similarity to subunits of Escherichia coli hydrogenase 3. In addition, all of the newly identified coo gene products show similarity to subunits of NADH-quinone oxidoreductase (energy-conserving NADH dehydrogenase I) from various eukaryotic and prokaryotic organisms. We have found that dicyclohexylcarbodiimide, an inhibitor of mitochondrial NADH dehydrogenase I (also called complex I), inhibits the CO-induced hydrogenase as well. We also show that expression of the cooMKLXUH operon is regulated by CO and the transcriptional activator CooA in a manner similar to that of the cooFSCTJ operon that encodes the subunits of CODH and related proteins.
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PMID:Characterization of the region encoding the CO-induced hydrogenase of Rhodospirillum rubrum. 889 19

The kinetics of H-D isotope exchange catalyzed by the thermostable hydrogenase from Thiocapsa roseopersicina have been studied by analysis of the exchange between D2 and H2O. The pH dependence of the exchange reaction was examined between pH 2.5 and pH 11. Over the whole pH range, HD was produced at a higher initial velocity than H2, with a marked optimum at pH 5.5; a second peak in the pH profile was observed at around pH 8.5. The rapid formation of H2 with respect to HD in the D2/H2O system is consistent with a heterolytic cleavage of D2 into D+ and an enzyme hydride that can both exchange with the solvent. The H-D-exchange activity was lower in the H2/D2O system than in the D2/H2O system. The other reactions catalyzed by the hydrogenase, H2 oxidation and H2 evolution, are pH dependent; the optimal pH were 9.5 for H2 uptake and 4.0 for H2 production. Treatment of the active form of hydrogenase by iodoacetamide led to a slow and irreversible inhibition of the H-D exchange. When iodo[1-14C]acetamide was incubated with hydrogenase, the radioactive labeling of the large subunit was higher for the enzyme activated under H2 than for the inactive oxidized form. Cysteine residues were identified as the alkylated derivative by amino acid analysis. Acetylene, which inhibits H-D exchange and abolishes the Ni-C EPR signal, protected the enzyme from irreversible inhibition by iodoacetamide. These data indicate that iodoacetamide can reach the active site of the H2-activated hydrogenase from T. roseopersicina. This was not found to be the case with the seleno hydrogenase from Desulfovibrio baculatus (now Desulfomicrobium baculatus). Cysteine modification by iodoacetamide upon activation of the enzyme concomitant with loss of H-D exchange indicates that reductive activation makes at least one Cys residue of the active site available for alkylation.
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PMID:Inhibition by iodoacetamide and acetylene of the H-D-exchange reaction catalyzed by Thiocapsa roseopersicina hydrogenase. 891 71

The H-D exchange reaction has been measured with the D2-H2O system, for Rhodobacter capsulatus JP91, which lacks the hupSL-encoded hydrogenase, and R. capsulatus BSE16, which lacks the HupUV proteins. The hupUV gene products, expressed from plasmid pAC206, are shown to catalyze an H-D exchange reaction distinguishable from the H-D exchange due to the membrane-bound, hupSL-encoded hydrogenase. In the presence of O2, the uptake hydrogenase of BSE16 cells catalyzed a rapid uptake and oxidation of H2, D2, and HD present in the system, and its activity (H-D exchange, H2 evolution in presence of reduced methyl viologen [MV+]) depended on the external pH, while the H-D exchange due to HupUV remained insensitive to external pH and O2. These data suggest that the HupSL dimer is periplasmically oriented, while the HupUV proteins are in the cytoplasmic compartment.
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PMID:HupUV proteins of Rhodobacter capsulatus can bind H2: evidence from the H-D exchange reaction. 898 13

A mesophilic, gram-negative, vibrio-shaped, marine, acetate-oxidizing sulfate reducer (strain B54) was isolated from a water-oil separation system on a North Sea oil platform. The optimum conditions for growth were 33 degrees C, pH 6.8 to 7.0, and concentrations of NaCl and MgCl2.6H2O of at least 1 and 0.3%, respectively. Of various organic acids tested, only acetate was used as an electron and carbon source. The presence of 2-oxoglutarate:dye oxidoreductase suggests acetate oxidation via an operative citric acid cycle. Even though growth of most Desulfobacter strains (including strain B54) did not occur on hydrogen, hydrogenase was detected at low activity. The growth yields were 4.6, 13.1, and 9.6 g of (dry weight) cells per mol of acetate oxidized with sulfate, sulfite, and thiosulfate, respectively, as electron acceptors. Strain B54 was able to fix dinitrogen. Desulforubidin and cytochromes of the c and b types were present. The G+C content of the DNA was 47 mol%. Strain B54 is most closely related to Desulfobacter latus, with a 16S rDNA sequence similarity of 98.1%. The DNA-DNA relatedness between them was 40.5%. On the basis of differences in genotypic, phenotypic, and immunological characteristics, we propose that strain B54 is a member of a new species, D. vibrioformis. It can be easily identified and distinguished from other Desulfobacter species by its large, vibrioshaped cells.
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PMID:Desulfobacter vibrioformis sp. nov., a sulfate reducer from a water-oil separation system. 933 18


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