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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)

Escherichia coli synthesizes a hydrogenase-linked formate dehydrogenase (FDHH) under anaerobic conditions in the absence of nitrate. In striking contrast to many other anaerobic-specific genes, which require DNA to be negatively supercoiled for expression, we have found that inhibition of DNA gyrase activity enhances expression from the gene (fdhF) encoding the selenopolypeptide of FDHH. Fusions of the 5' flanking region of fdhF and the structural gene of lacZ were used to determine fdhF expression under varying conditions. Chemical inhibitors and a temperature-sensitive mutant allowed in vivo inhibition of gyrase activity. In each case, concomitant with gyrase inhibition there was a substantial increase in the induction of fusion protein synthesis. This enhancement of expression is observed for the intact fdhF gene residing on the chromosome as well as the fusion gene in a multicopy plasmid. Inhibition of gyrase activity will partially overcome the inhibition of fdhF expression due to nitrate but does not allow fusion protein synthesis in the presence of oxygen.
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PMID:Anaerobic induction of Escherichia coli formate dehydrogenase (hydrogenase-linked) is enhanced by gyrase inactivation. 282 13

The opal termination codon UGA is used in both prokaryotic and eukaryotic species to direct the specific insertion of selenocysteine into certain selenium-dependent enzymes. So far a formate dehydrogenase (hydrogenase-linked) of Escherichia coli and glutathione peroxidases of murine, human and rat origin have been identified as enzymes containing selenocysteine residues encoded by UGA. A novel seryl-tRNA, anticodon UCA, that specifically recognizes the UGA codon is required for selenocysteine incorporation into formate dehydrogenase. A eukaryotic UGA suppressor tRNA with UCA anticodon that accepts serine and is phosphorylated to O-phosphoseryl-tRNA may have a corresponding function in glutathione peroxidase synthesis. Other factors required for the unusual usage of the in-frame UGA codons to specify selenocysteine incorporation and the biochemical mechanism involved in distinguishing these from normal UGA termination codons are discussed.
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PMID:Selenocysteine, a highly specific component of certain enzymes, is incorporated by a UGA-directed co-translational mechanism. 297 58

Anaerobic growth in the presence of 0.6 mM NiCl2 was able to restore hydrogenase and benzyl-viologen-linked formate dehydrogenase activities to a mutant (FD12), which is normally defective in these activities. This mutant carries a mutation located near minute 58 in the genome. Hydrogenase isoenzyme I and II activities were restored along with the hydrogenase activity that forms part of the formate hydrogen lyase system. A plasmid (pRW1) was constructed, containing a 4.8 kb chromosomal DNA insert, which was able to complement the lesion in mutant FD12. Further mutants with mutations near 58 minutes on the chromosome, and which lacked hydrogenase and formate dehydrogenase activities were isolated. These mutants were divided into three groups. Class I mutants were restored to the wild-type phenotype either by growth with 0.6 mM NiCl2 or following transformation with pRW1. Class II mutants were also complemented by pRW1 but were unaffected by growth with NiCl2. Class III mutants were unaffected by both pRW1 and growth with NiCl2. The cloned 4.8 kb fragment of chromosomal DNA therefore encodes two genes essential for hydrogenase activity. Restriction analysis indicates that the cloned DNA is the same as a fragment that has previously been cloned and which complements the hydB locus (Sankar et al. (1985) J. Bacteriol., 162, 353-360). None of the three classes of mutants possess mutations in hydrogenase structural genes.
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PMID:Pleiotropic hydrogenase mutants of Escherichia coli K12: growth in the presence of nickel can restore hydrogenase activity. 301 43

Electron transport-coupled phosphorylation with fumarate as terminal acceptor in Wolinella succinogenes yields less than 1 ATP/2 electrons. The delta mu H generated by the electron transport is 0.18 V and the H+/electron ratio is 1. The electron transport chain is made up of two dehydrogenases (hydrogenase and formate dehydrogenase) that catalyze the reduction of menaquinone, and fumarate reductase which catalyzes the oxidation of menaquinol. C-type cytochromes are not involved. The phosphorylative electron transport with sulfur as terminal acceptor in W. succinogenes or Desulfuromonas acetoxidans does not involve known quinones. The ATP yields should be even smaller than those with fumarate. Succinate oxidation by sulfur, which is a catabolic reaction in D. acetoxidans, is accomplished by reversed electron transport.
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PMID:Phorphorylative electron transport chains lacking a cytochrome bc1 complex. 301 97

Synthesis of formate dehydrogenase coupled to formate hydrogenlyase activity in Escherichia coli was found to require the product of the fhlA gene. Transcription of fdhF, the gene coding for the 80-kilodalton (kDa) selenopeptide of formate dehydrogenase, was not detected in an fhlA genetic background. Mutations in the fhlA gene also abolished production of the hydrogenase activity associated with formate hydrogenlyase activity. The fhlA gene resides next to the hydB gene at 59 min in the E. coli chromosome, and the two genes are transcribed in opposite directions. The fhlA gene codes for a 78-kDa protein. A neighboring gene, fdv, codes for an 82-kDa protein, and the physiological role of this gene product is unknown, although a role in H2 metabolism can be detected.
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PMID:Gene-product relationships of fhlA and fdv genes of Escherichia coli. 305

Two mutant strains of Escherichia coli, AK11 and AK22, express normal levels of hydrogenase activity, assayed by deuterium exchange, when grown on glucose or complex medium but cannot reduce methyl viologen by H2 nor grow on fumarate plus H2. The mutant strains also lack formate hydrogenlyase and formate dehydrogenase activities. The mutation in these strains was located near minute 17 of the genome map and a single mutation was shown to be responsible for loss of both hydrogen uptake and formate-related activities. Membrane vesicles and solubilized membranes of strains AK11 and AK22 were capable of methyl viologen reduction by H2 and had the normal complement of hydrogenase isoenzymes 1 and 2. Intact cells of the mutant strains could reduce fumarate by H2 but could not grow under these conditions. A plasmid, pAK11, was isolated, as well as smaller plasmids derived from it, which restored the hydrogen uptake activities in the two mutant strains, the smallest active DNA fragment being 1.4 kb. The formate activities were partially restored by some of the plasmids. The plasmids which restored hydrogen uptake activities led to synthesis of a polypeptide of subunit molecular mass 30 kDa.
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PMID:Isolation of a gene required for growth of Escherichia coli on fumarate and H2. 307 54

The Mu dl (ApR lac) bacteriophage was used to generate mutants of Escherichia coli which were defective in formate hydrogenlyase. Three mutants were chosen for further analysis: they lacked hydrogenase (hydrogen: benzyl viologen oxidoreductase) activity, but produced normal levels of fumarate reductase activity and two- to three-fold reduced levels of benzyl viologen (BV)-dependent formate dehydrogenase activity. Two of them (hydC) were shown to contain about 4-fold reduced amounts of formate hydrogenlyase and fumarate-dependent H2 uptake activities. The third one (hydD) was totally devoid of both activities. Their insertion sites were located at 77 min on the E. coli map. Subdivision of these mutants into two classes was subsequently based on the restoration capacity of hydrogenase activity with high concentration of nickel in the growth media. Addition of 500 microM NiCl2 led to a complete recovery of hydrogenase activity, and to the concomitant restoration of normal BV-linked formate dehydrogenase, formate hydrogenlyase and fumarate-dependent H2 uptake activities in the hydC mutants. The hydD mutant was insensitive to the effect of nickel. Expression of the lac operon in hydC and hydD mutants was induced by anaerobiosis. It was not increased by the addition of formate under anaerobic conditions. The presence of nitrate resulted in slightly reduced beta-galactosidase activities in the hydC mutants, whereas those found in the hydD mutant reached only one third of the level obtained in its absence. Fumarate had no effect on both classes. Moreover, in contrast to the hydD locus, the hydC::Mu dl fusions were found to be dependent upon the positive control exerted by the nirR gene product and were totally repressed by an excess of nickel. In addition, the low levels of overall hydrogenase-dependent activities found in a nirR strain were also relieved by the presence of nickel. Our results strongly suggest that the pleiotropic regulatory gene nirR is essential for the expression of a gene (hydC) involved in either transport or processing of nickel in the cell, whose alteration leads to a loss of hydrogenase activity.
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PMID:Genetic and physiological characterization of new Escherichia coli mutants impaired in hydrogenase activity. 308 8

Methanococcus thermolithotrophicus is a methanogenic archaebacterium that can use either H2 or formate as its source of electrons for reduction of CO2 to methane. Growth and suspended-whole-cell experiments show that H2 plus CO2 methanogenesis was constitutive, while formate methanogenesis required adaptation time; selenium was necessary for formate utilization. Cells grown on formate had 20 to 100 times higher methanogenesis rates on formate than cells grown on H2-CO2 and transferred into formate medium. Enzyme assays with crude extracts and with F420 or methyl viologen as the electron acceptor revealed that hydrogenase was constitutive, while formate dehydrogenase was regulated. Cells grown on formate had 10 to 70 times higher formate dehydrogenase activity than cells grown on H2-CO2 with Se present in the medium; when no Se was added to H2-CO2 cultures, even lower activities were observed. Adaptation to and growth on formate were pH dependent, with an optimal pH for both about one pH unit above that optimal for H2-CO2 (pH 5.8 to 6.5). When cells were grown on H2-CO2 in the presence of formate, formate (greater than or equal to 50 mM) inhibited both growth and methanogenesis at pH 5.8 to 6.2, but not at pH greater than 6.6. Both acetate and propionate produced similar inhibition. Formate inhibition was also observed in Methanospirillum hungatei.
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PMID:Relationship of formate to growth and methanogenesis by Methanococcus thermolithotrophicus. 309 65

Two classes of mutants defective in benzyl viologen-linked formate dehydrogenase (FDH-BV) activity were isolated from Escherichia coli K12. Class I consisted of four mutants which were specifically devoid of FDH-BV activity. Their mutation mapped between the ssb and melA genes at 92 min on the genome, at a site recently designated fdhF by Pecher et al. (1985). The direction of transcription of gene fdhF was found to be counterclockwise on the E. coli chromosome in one Mudl(Aprlac) fusion mutant. Expression of the lac operon in this mutant was induced by formate and repressed by nitrate, nitrite or trimethylamine N-oxide. It was found to be dependent on the positive control exerted by the fdhA, B and C genes, possibly involved in selenium incorporation, and by an hydB gene affecting the formate hydrogenlyase pathway. Class II, represented by one Mudl(Aprlac) mutant, exhibited no FDH-BV activity and a reduced level of hydrogenase activity. The relevant fdv mutation was shown to be located at 58 min and to affect the expression of fdhF.
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PMID:Regulation of the fdhF gene encoding the selenopolypeptide for benzyl viologen-linked formate dehydrogenase in Escherichia coli. 311 41

Localized mutagenesis was used to obtain rha-linked mutations in Salmonella typhimurium, resulting in defects in the nitrate reductase-linked formate dehydrogenase (FDHN). The fdn mutants obtained fell into two groups which differed in several respects. Group I isolates lacked FDHN activity under all conditions examined and exhibited wild-type levels of the hydrogenase-linked formate dehydrogenase (FDHH). Group II isolates appeared defective in FDHN only when freshly prepared extracts were assayed; restoration of both FDHN and formate-nitrate reduction activity occurred on incubation of extracts for 2 to 3 h. Protease inhibitors prevented restoration. Group II isolates were also characterized by a conditional FDHH activity; this activity was absent unless the growth medium designed to optimize wild-type FDHH was altered either by lowering glucose concentration or by adding thiosulfate. Cotransduction of fdn with rha ranged from 4 to 22% for the group I isolates and from 20 to 40% for the group II isolates. Temperature-sensitive isolates from both groups synthesized FDHN activity with altered thermostability. In vitro complementation occurred in mixed extracts of amber mutants of the two respective classes. The results are consistent with two distinct rha-linked fdn genes, for which we suggest using the designations fdnB (group I) and fdnC (group II).
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PMID:Formate-nitrate respiration in Salmonella typhimurium: studies of two rha-linked fdn genes. 327 11


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