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)

In the anaerobic respiration chain of "Dehalobacter restrictus," dihydrogen functioned as the electron donor and tetrachloroethene (PCE) functioned as the electron acceptor. The hydrogenase faced the periplasm, and the PCE reductase faced the cytoplasmic side of the membrane. Both activities were associated with the cytoplasmic membrane. UV spectroscopy showed that membrane-bound menaquinone (MQ) was reduced by oxidation of H2 and reoxidized by reduction of PCE, indicating that MQ functions as an electron mediator. Fast proton liberation (t1/2 = 6 +/- 2 s) during electron transport from H2 to PCE and to trichloroethene (TCE) after addition of either PCE or TCE to H2-saturated cells resulted in an extrapolated H+/e- ratio of 1.25 +/- 0.2. This ratio indicated that besides the formation of protons upon oxidation of H2, vectorial translocation of protons from the inside to the outside could also occur. Proton liberation was inhibited by carbonylcyanide m-chlorophenylhydrazone (CCCP), 2-n-heptyl-4-hydroxyquinoline N-oxide (HOQNO), and CuCl2. Fast proton liberation with an H+/e- ratio of 0.65 +/- 0.1 was obtained after addition of the MQ analog 2,3-dimethyl-1,4-naphthoquinone (DMN) as an oxidant pulse. This acidification was also inhibited by CCCP, HOQNO, and CuCl2. Oxidation of reduced DMN by PCE was not associated with fast acidification. The results with DMN indicate that the consumption and release of protons associated with redox reactions of MQ during electron transfer from H2 to PCE both occurred at the cytoplasmic side of the membrane. The PCE reductase was photoreversibly inactivated by 1-iodopropane, indicating that a corrinoid was involved in the PCE reduction.
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PMID:The proton/electron ration of the menaquinone-dependent electron transport from dihydrogen to tetrachloroethene in "Dehalobacter restrictus". 863 34

Dehalococcoides ethenogenes strain 195 reductively dechlorinates tetrachloroethene (PCE) and trichloroethene (TCE) to vinyl chloride and ethene using H2 as an electron donor. PCE- and TCE-reductive dehalogenase (RD) activities were mainly membrane associated, whereas only about 20% of the hydrogenase activity was membrane associated. Experiments with methyl viologen (MV) were consistent with a periplasmic location for the RDs or a component feeding electrons to them. The protonophore uncoupler tetrachlorosalicylanilide did not inhibit reductive dechlorination in cells incubated with H2 and PCE and partially restored activity in cells incubated with the ATPase inhibitor N,N'-dicyclohexylcarbodiimide. Benzyl viologen or diquat (Eo' approximately -360 mV) supported reductive dechlorination of PCE or TCE at rates comparable to MV (-450 mV) in cell extracts.
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PMID:Characterization of hydrogenase and reductive dehalogenase activities of Dehalococcoides ethenogenes strain 195. 1574 76

DNA and RNA transcripts, particularly of genes of functional importance in the reductively dechlorinating microbe Dehalococcoides, are increasingly being studied as potential molecular bioindicators of reductive dechlorination. Ideally, mRNA bioindicators would be informative both qualitatively (with respect to dechlorination end point and substrate range) and quantitatively (with respectto activity rates). Here, we examined pseudo-steady-state mRNA levels in Dehalococcoides-containing microcosms continuously fed PCE at various loading rates. We characterized gene transcript abundance of potential Dehalococcoides bioindicators of reductive dechlorination, including 16S rRNA, and genes encoding an annotated formate dehydrogenase (Fdh), the hydrogenase (H2ase) Hup, and the reductive dehalogenases (RDases) TceA, DET1559, PceA, and DET1545. Increases in steady PCE loading rate led to corresponding increases in PCE respiration rate (1.5 +/- 0.1, 2.5 +/- 0.3, 4.8 +/- 0.1, and 9.2 +/- 0.5 micromol/L/hr). We also observed that pseudo-steady-state expression levels of most functional targets increase linearly over PCE respiration rates of 1.5-4.8 micromol/L/hr, with Fdh, Hup, and TceA transcripts increasing by approximately 2 x 10(10) copies per mL of culture for every micromol/L/hr increase in chloroethene respiration rate, and DET1559 and PceAtranscripts increasing by approximately9 x 10(9) copies per mL of culture, butthat increased respiration rates of 9.2 micromol/L/hr did not necessarily lead to corresponding increases in transcript levels.
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PMID:Correlation of respiratory gene expression levels and pseudo-steady-state PCE respiration rates in Dehalococcoides ethenogenes. 1828 40

Tetrachloroethene (PCE) and trichloroethene (TCE) are prevalent groundwater contaminants that can be completely reductively dehalogenated by some "Dehalococcoides" organisms. A Dehalococcoides-organism-containing microbial consortium (referred to as ANAS) with the ability to degrade TCE to ethene, an innocuous end product, was previously enriched from contaminated soil. A whole-genome photolithographic microarray was developed based on the genome of "Dehalococcoides ethenogenes" 195. This microarray contains probes designed to hybridize to >99% of the predicted protein-coding sequences in the strain 195 genome. DNA from ANAS was hybridized to the microarray to characterize the genomic content of the ANAS enrichment. The microarray results revealed that the genes associated with central metabolism, including an apparently incomplete carbon fixation pathway, cobalamin-salvaging system, nitrogen fixation pathway, and five hydrogenase complexes, are present in both strain 195 and ANAS. Although the gene encoding the TCE reductase, tceA, was detected, 13 of the 19 reductive dehalogenase genes present in strain 195 were not detected in ANAS. Additionally, 88% of the genes in predicted integrated genetic elements in strain 195 were not detected in ANAS, consistent with these elements being genetically mobile. Sections of the tryptophan operon and an operon encoding an ABC transporter in strain 195 were also not detected in ANAS. These insights into the diversity of Dehalococcoides genomes will improve our understanding of the physiology and evolution of these bacteria, which is essential in developing effective strategies for the bioremediation of PCE and TCE in the environment.
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PMID:Comparative genomics of "Dehalococcoides ethenogenes" 195 and an enrichment culture containing unsequenced "Dehalococcoides" strains. 1835 38

Gene transcripts corresponding to 16S rRNA, the hydrogenase (H2ase) Hup, a sequence annotated asformate dehydrogenase (Fdh) and reductive dehalogenases (RDases) TceA, PceA, DET1559, and DET1545 in Dehalococcoides ethenogenes strain 195 (DET) hold promise as potential bioindicators of the dehalorespiration of chlorinated ethenes. Here, we present quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR) data taken from DET-containing mixed culture microcosms (4.4 x 10(8) DET 16S rRNA gene copies/mL) operated under continuous-feed conditions, with the aim of clarifying the relationships between pseudosteady-state abundances of bioindicator transcripts and respiration rate of various substrates: tetrachloroethene (PCE), trichloroethene (TCE), and cis-1,2-dichloroethene (cDCE). Results from PCE-fed microcosms suggested an induction threshold for transcription of some bioindicator genes between chloroethene respiration rates of 2.1 and 9.5 microeeq/L/hr. Putative RDase genes DET1559 and DET1545, however, were up-regulated at low PCE respiration rates and may be functionally significant when substrate levels are low. Data from PCE-fed microcosms operated at saturation kinetics indicated that a high respiration rate was not necessarily associated with a correspondingly high bioindicator transcript abundance. From these microcosms we calculated an approximate yield value of 1.6 x 10(8) 16S rRNA gene copies (cells) per micromol Cl- released and estimated a kmax of PCE respiration of 3 x 10(-9) micromol Cl- per 16S rRNA gene copy per day. TCE- and cDCE-fed microcosm studies indicated that Fdh, Hup, and TceA were the most abundant transcripts and could make suitable choices as bioindicators of activity for these substrates. Hup transcripts could be positively correlated to respiration rate (between approximately 8 and 45 microeeq/L/hr) regardless of chloroethene substrate, with transcript levels predicted to increase by 1.8 x 10(9) copies/mL culture for every/eeq/ L/hr increase in respiration rate (R2 = 0.90). Although RDase transcripts may provide information on substrate range, H2ase transcripts may be better indicators of per cell respiration rates.
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PMID:Dehalococcoides' gene transcripts as quantitative bioindicators of tetrachloroethene, trichloroethene, and cis-1,2-dichloroethene dehalorespiration rates. 1875 54

The organohalide-respiring Epsilonproteobacterium Sulfurospirillum multivorans is able to grow with hydrogen as electron donor and with tetrachloroethene (PCE) as electron acceptor; PCE is reductively dechlorinated to cis-1,2-dichloroethene. Recently, a genomic survey revealed the presence of four gene clusters encoding NiFe hydrogenases in its genome, one of which is presumably periplasmic and membrane-bound (MBH), whereas the remaining three are cytoplasmic. To explore the role and regulation of the four hydrogenases, quantitative real-time PCR and biochemical studies were performed with S. multivorans cells grown under different growth conditions. The large subunit genes of the MBH and of a cytoplasmic group 4 hydrogenase, which is assumed to be membrane-associated, show high transcript levels under nearly all growth conditions tested, pointing toward a constitutive expression in S. multivorans. The gene transcripts encoding the large subunits of the other two hydrogenases were either not detected at all or only present at very low amounts. The presence of MBH under all growth conditions tested, even with oxygen as electron acceptor under microoxic conditions, indicates that MBH gene transcription is not regulated in contrast to other facultative hydrogen-oxidizing bacteria. The MBH showed quinone-reactivity and a characteristic UV/VIS spectrum implying a cytochrome b as membrane-integral subunit. Cell extracts of S. multivorans were subjected to native polyacrylamide gel electrophoresis (PAGE) and hydrogen oxidizing activity was tested by native staining. Only one band was detected at about 270 kDa in the particulate fraction of the extracts, indicating that there is only one hydrogen-oxidizing enzyme present in S. multivorans. An enrichment of this enzyme and SDS PAGE revealed a subunit composition corresponding to that of the MBH. From these findings we conclude that the MBH is the electron-donating enzyme system in the PCE respiratory chain. The roles for the other three hydrogenases remain unproven. The group 4 hydrogenase might be involved in hydrogen production upon fermentative growth.
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PMID:The NiFe Hydrogenases of the Tetrachloroethene-Respiring Epsilonproteobacterium Sulfurospirillum multivorans: Biochemical Studies and Transcription Analysis. 2837 66

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