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)

Cyanobacteria may possess several enzymes that are directly involved in dihydrogen metabolism: nitrogenase(s) catalyzing the production of hydrogen concomitantly with the reduction of dinitrogen to ammonia, an uptake hydrogenase (encoded by hupSL) catalyzing the consumption of hydrogen produced by the nitrogenase, and a bidirectional hydrogenase (encoded by hoxFUYH) which has the capacity to both take up and produce hydrogen. This review summarizes our knowledge about cyanobacterial hydrogenases, focusing on recent progress since the first molecular information was published in 1995. It presents the molecular knowledge about cyanobacterial hupSL and hoxFUYH, their corresponding gene products, and their accessory genes before finishing with an applied aspect--the use of cyanobacteria in a biological, renewable production of the future energy carrier molecular hydrogen. In addition to scientific publications, information from three cyanobacterial genomes, the unicellular Synechocystis strain PCC 6803 and the filamentous heterocystous Anabaena strain PCC 7120 and Nostoc punctiforme (PCC 73102/ATCC 29133) is included.
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PMID:Hydrogenases and hydrogen metabolism of cyanobacteria. 1187 25

Moderate levels of urease activity (ca. 300 mU mg(-1)) were detected in Rhizobium leguminosarum bv. viciae UPM791 vegetative cells. This activity did not require urea for induction and was partially repressed by the addition of ammonium into the medium. Lower levels of urease activity (ca. 100 mU mg(-1)) were detected also in pea bacteroids. A DNA region of ca. 9 kb containing the urease structural genes ( ureA, ureB and ureC), accessory genes ( ureD, ureE, ureF, and ureG), and five additional ORFs ( orf83, orf135, orf207, orf223, and orf287) encoding proteins of unknown function was sequenced. Three of these ORFs ( orf83, orf135 and orf207) have a homologous counterpart in a gene cluster from Sinorhizobium meliloti, reported to be involved in urease and hydrogenase activities. R. leguminosarum mutant strains carrying Tn 5 insertions within this region exhibited a urease-negative phenotype, but induced wild-type levels of hydrogenase and nitrogenase activities in bacteroids. orf287 encodes a potential transmembrane protein with a C-terminal GGDEF domain. A mutant affected in orf287 exhibited normal levels of urease activity in culture cells. Experiments aimed at cross-complementing Ni-binding proteins required for urease and hydrogenase synthesis (UreE and HypB, respectively) indicated that these two proteins are not functionally interchangeable in R. leguminosarum.
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PMID:Characterization of the urease gene cluster from Rhizobium leguminosarum bv. viciae. 1188 82

In order to determine the effects of the deletion of hydrogenase genes on nitrogenase-based photobiological H(2) productivity by heterocystous N(2)-fixing cyanobacteria, we have constructed three hydrogenase mutants from Anabaena sp. PCC 7120: hupL(-) (deficient in the uptake hydrogenase), hoxH(-) (deficient in the bidirectional hydrogenase), and hupL(-)/ hoxH(-) (deficient in both genes). The hupL(-) mutant produced H(2) at a rate four to seven times that of the wild-type under optimal conditions. The hoxH(-) mutant produced significantly lower amounts of H(2) and had slightly lower nitrogenase activity than wild-type. H(2) production by the hupL(-)/ hoxH(-) mutant was slightly lower than, but almost equal to, that of the hupL(-) mutant. The efficiency of light energy conversion to H(2) by the hupL(-) mutant at its highest H(2) production stage was 1.2% at an actinic visible light intensity of 10 W/m(2) (PAR) under argon atmosphere. These results indicate that deletion of the hupL gene could be employed as a source for further improvement of H(2) production in a nitrogenase-based photobiological H(2) production system.
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PMID:Disruption of the uptake hydrogenase gene, but not of the bidirectional hydrogenase gene, leads to enhanced photobiological hydrogen production by the nitrogen-fixing cyanobacterium Anabaena sp. PCC 7120. 1195 44

Metallocluster-containing enzymes catalyze some of the most basic redox transformations in the biosphere. The reactions catalyzed by these enzymes typically involve small molecules such as N2, CO, and H2 that are used to generate both chemical building blocks and energy for metabolic purposes. During the past decade, structures have been established for the iron-sulfur-based metalloclusters present in the molybdenum nitrogenase, the iron-only hydrogenase, and the nickel-carbon monoxide dehydrogenase, and for the copper-sulfide-based cluster in nitrous oxide reductase. Although these clusters are built from interactions observed in simpler metalloproteins, they contain novel features that may be relevant for their catalytic function. The mechanisms of metallocluster-containing enzymes are still poorly defined, and represent substantial and continuing challenges to biochemists, biophysicists, and synthetic chemists. These proteins also provide a window into the union of the biological and inorganic worlds that may have been relevant to the early evolution of biochemical catalysis.
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PMID:Great metalloclusters in enzymology. 1204 96

Nitrogenase-mediated H(2) accumulation of Rhodobacter sphaeroides under photoheterotrophic conditions is reduced directly by the hydrogenase activity catalyzing H(2) uptake and indirectly by energy-demanding metabolic processes such as poly-beta-hydroxybutyrate (PHB) formation. H(2) accumulation of R. sphaeroides was examined during cell growth under illumination of 15, 7, and 3 W/m(2). Mutations in either hupSL (H(2)-uptake hydrogenase) or phbC (PHB synthase) had no effect on nitrogenase activity. The nitrogenase activity of R. sphaeroides grown at 15 W/m(2), however, was 70% higher than that of cells grown at 3 W/m(2), while the H(2)-uptake hydrogenase activity was approximately 3-fold higher in the same comparison. Accordingly, H(2) uptake by hydrogenase, monitored by measuring the difference in H(2) accumulation between a hupSL-deletion mutant and the corresponding parental strain, appeared to reach a maximum level as illumination was increased to 15 W/m(2). On the other hand, the surplus energy due to lack of PHB formation led to a fixed increase in H(2) accumulation independent of light intensity, reflecting the fact that the cellular PHB content was not changed significantly depending on light intensity. Therefore, H(2) uptake by hydrogenase should be suppressed to achieve higher H(2) accumulation of R. sphaeroides, especially at 15 W/m(2).
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PMID:Reductive effect of H(2) uptake and poly-beta-hydroxybutyrate formation on nitrogenase-mediated H(2) accumulation of Rhodobacter sphaeroides according to light intensity. 1238 56

The hydrogen-uptake genes were transferred into wild Rhizobium arachis Ra strains (Hup-, Nif+, Apr) by triparental mating using pRK2013 as help plasmid. A transconjugant R. arachis Rz34-2(Hup+, Nif+, Apr, Tcr) which expressed high activities of hydrogenase and nitrogenase under free-living and symbiotic state was screened. Peanut inoculation test with recipient R. arachis Ra34, transcojugant Rz34-2 and control strain R. arachis L8-3 (Hup+, Nif+) was carried out respectively. The results showed that, compare to treatment without inoculation, inoculation with R. arachis Ra34 and R. arachis L8-3, the dry weight of leaf inoculated with transconjuant Rz34-2 increased 6.2%, 7.6% and 6.3% respectively; the N-content of seed increased 8.8%, 10.0% and 6.0%; the output increased 18.8%, 10.5% and 10.7%. This suggested that legume plants inoculated with Rhizobium strains (Hup+) were more efficient to accumulate N and to increase its output.
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PMID:[Studies on transference of hydrogenase genes of Rhizobium arachis]. 1255 6

Transition metal complexes are located at the active sites of a number of enzymes involved in intriguing biochemical reactions. These complexes can exhibit a wide variety of chemical reactivity due to the ease at which transition metals can adopt different coordination environments and oxidation states. Crystallography has been a powerful technique for examining the structure and conformational variability of complex biological metallocenters. In particular, the past ten years have provided a wealth of structural information and several surprises concerning the metallocenters at the active sites of nitrogenase, hydrogenase and carbon monoxide dehydrogenase/acetyl-coenzyme A synthase.
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PMID:Surprising cofactors in metalloenzymes. 1272 16

Several unicellular and filamentous, nitrogen-fixing and non-nitrogen-fixing cyanobacterial strains have been investigated on the molecular and the physiological level in order to find the most efficient organisms for photobiological hydrogen production. These strains were screened for the presence or absence of hup and hox genes, and it was shown that they have different sets of genes involved in H(2) evolution. The uptake hydrogenase was identified in all N(2)-fixing cyanobacteria, and some of these strains also contained the bidirectional hydrogenase, whereas the non-nitrogen fixing strains only possessed the bidirectional enzyme. In N(2)-fixing strains, hydrogen was mainly produced by the nitrogenase as a by-product during the reduction of atmospheric nitrogen to ammonia. Therefore, hydrogen production was investigated both under non-nitrogen-fixing conditions and under nitrogen limitation. It was shown that the hydrogen uptake activity is linked to the nitrogenase activity, whereas the hydrogen evolution activity of the bidirectional hydrogenase is not dependent or even related to diazotrophic growth conditions. With regard to large-scale hydrogen evolution by N(2)-fixing cyanobacteria, hydrogen uptake-deficient mutants have to be used because of their inability to re-oxidize the hydrogen produced by the nitrogenase. On the other hand, fermentative H(2) production by the bidirectional hydrogenase should also be taken into account in further investigations of biological hydrogen production.
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PMID:Cyanobacterial H(2) production -- a comparative analysis. 1456 21

Structural genes coding for two membrane-associated NiFe hydrogenases in the phototrophic purple sulfur bacterium Thiocapsa roseopersicina (hupSL and hynSL) have recently been isolated and characterized. Deletion of both hydrogenase structural genes did not eliminate hydrogenase activity in the cells, and considerable hydrogenase activity was detected in the soluble fraction. The enzyme responsible for this activity was partially purified, and the gene cluster coding for a cytoplasmic, NAD+-reducing NiFe hydrogenase was identified and sequenced. The deduced gene products exhibited the highest similarity to the corresponding subunits of the cyanobacterial bidirectional soluble hydrogenases (HoxEFUYH). The five genes were localized on a single transcript according to reverse transcription-PCR experiments. A sigma54-type promoter preceded the gene cluster, suggesting that there was inducible expression of the operon. The Hox hydrogenase was proven to function as a truly bidirectional hydrogenase; it produced H2 under nitrogenase-repressed conditions, and it recycled the hydrogen produced by the nitrogenase in cells fixing N2. In-frame deletion of the hoxE gene eliminated hydrogen evolution derived from the Hox enzyme in vivo, although it had no effect on the hydrogenase activity in vitro. This suggests that HoxE has a hydrogenase-related role; it likely participates in the electron transfer processes. This is the first example of the presence of a cyanobacterial-type, NAD+-reducing hydrogenase in a phototrophic bacterium that is not a cyanobacterium. The potential physiological implications are discussed.
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PMID:Cyanobacterial-type, heteropentameric, NAD+-reducing NiFe hydrogenase in the purple sulfur photosynthetic bacterium Thiocapsa roseopersicina. 1476 47

Root nodule development, and seasonal patterns of nodular nitrogenase and hydrogenase activities were determined for 5- to 8-year old black alder (Alnus glutinosa (L.) Gaertn.) and Russian olive (Elaeagnus angustifolia L.) interplanted with black walnut (Juglans nigra L.) on bottomland and upland sites in central Illinois, USA. Black alder produced nodules at both sites, but Russian olive did so only at the bottomland site. Nodular nitrogenase activity was detectable in both species over a 220-day period. Maximum, midday rates of nitrogenase activity (acetylene reduction) of 15 to 20 micromoles C(2)H(4) per g dry nodule per hour were maintained by black alder for approximately 150 days at both the upland and bottomland sites. Near maximum rates of nodular nitrogenase activity were maintained for a similar period by Russian olive at the lowland site, although specific nitrogenase activity was approximately 25% lower than in black alder owing to a larger proportion of necrotic nodular tissue in Russian olive. In both species, nitrogenase activity increased exponentially with temperature between 10 degrees C and 20 to 25 degrees C. No net hydrogen evolution by nodules of either species was detected at any time during the assay period, indicating efficient hydrogenase systems were operating under the conditions of the field assay. Height of black walnut interplanted with nodulated black alder and Russian olive was greater than that of black walnut grown in pure stands.
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PMID:Seasonal changes in nodular nitrogenase activity of Alnus glutinosa and Elaeagnus angustifolia. 1497 86


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