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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)

We reported earlier the identification of two Azotobacter vinelandii open reading frames (ORFs), ORF1 and ORF2, downstream from the hydrogenase structural genes (Chen, J.C. and Mortenson, L.E. (1992) Biochim. Biophys. Acta 1131, 122-124). Sequencing of 6008 base pairs of DNA immediately downstream from ORF2 revealed six additional ORFs (ORF3 through ORF8). All six ORFs are transcribed from the same DNA strand as that of the ORF1 and ORF2. Deduced amino acid sequences of ORF3 through ORF5, and those of ORF4, ORF5, ORF7 and ORF8 have strong homology with genes required for dihydrogen (H2) metabolism in Rhodobacter capsulatus and in Escherichia coli, respectively. ORF4, ORF5, ORF6 and ORF8 would encode for polypeptides containing one or more 'Cys-X-X-Cys' motifs. The predicted products of ORF5 and ORF6 each contain a histidine-rich region, and the product of ORF5 also includes a 'Cys-Thr-Val-Cys-Gly-Cys' region near its amino-terminus. Implications of these findings with respect to metal binding, transport and incorporation, to hydrogenase assembly and to H2 metabolism are discussed.
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PMID:Identification of six open reading frames from a region of the Azotobacter vinelandii genome likely involved in dihydrogen metabolism. 161 Sep 1

Azotobacter vinelandii contains a heterodimeric, membrane-bound [NiFe]hydrogenase capable of catalyzing the reversible oxidation of H2. The beta and alpha subunits of the enzyme are encoded by the structural genes hoxK and hoxG, respectively, which appear to form part of an operon that contains at least one further potential gene (open reading frame 3 [ORF3]). In this study, determination of the nucleotide sequence of a region of 2,344 bp downstream of ORF3 revealed four additional closely spaced or overlapping ORFs. These ORFs, ORF4 through ORF7, potentially encode polypeptides with predicted masses of 22.8, 11.4, 16.3, and 31 kDa, respectively. Mutagenesis of the chromosome of A. vinelandii in the area sequenced was carried out by introduction of antibiotic resistance gene cassettes. Disruption of hoxK and hoxG by a kanamycin resistance gene abolished whole-cell hydrogenase activity coupled to O2 and led to loss of the hydrogenase alpha subunit. Insertional mutagenesis of ORF3 through ORF7 with a promoterless lacZ-Kmr cassette established that the region is transcriptionally active and involved in H2 oxidation. We propose to call ORF3 through ORF7 hoxZ, hoxM, hoxL, hoxO, and hoxQ, respectively. The predicted hox gene products resemble those encoded by genes from hydrogenase-related operons in other bacteria, including Escherichia coli and Alcaligenes eutrophus.
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PMID:Nucleotide sequences and genetic analysis of hydrogen oxidation (hox) genes in Azotobacter vinelandii. 162 46

An 8kb segment of DNA from the 58/59 min region of the E. coli chromosome, which complements the defect of a mutant devoid of hydrogenase 3 activity, has been sequenced. Eight open reading frames were identified which are arranged in a transcriptional unit; all open reading frames were transcribed and translated in vivo in a T7 promoter/polymerase system. Analysis of the amino acid sequences derived from the nucleic acid sequences revealed that one of them, open reading frame 5 (ORF5), exhibits significant sequence similarity to conserved regions of the large subunit from Ni/Fe hydrogenases. Two of the open reading frames (orf2, orf6) code for proteins apparently carrying iron-sulphur clusters of the 4Fe/4S ferredoxin type. The product of one of the open reading frames, orf7, displays extensive sequence similarity with protein G from the chloroplast electron transport chain. ORF3 and ORF4, on the other hand, are extremely hydrophobic proteins with nine and six putative transmembrane helices, respectively. Over a limited hydrophilic sequence stretch, bordered by putative transmembrane areas, ORF3 and ORF4 exhibit homology with subunits 4 and 1 of mitochondrial and plastid NADH-ubiquinol oxidoreductases, respectively. The operon described, therefore, appears to comprise genes for redox carriers linking formate oxidation to proton reduction and for a hydrogenase of hitherto unique composition.
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PMID:Nucleotide sequence and expression of an operon in Escherichia coli coding for formate hydrogenlyase components. 218 44

To clarify the role of the heterocyst-specific [2Fe-2S] ferredoxin in cyanobacterial nitrogen fixation, mutational analysis of the Anabaena 7120 fdxH gene region was carried out. First, the DNA sequence of the wild-type 3509-bp EcoRI fragment downstream of the fdxH gene was determined. Genes homologous to ORF3 from the fdxH gene regions of A. variabilis and Plectonema boryanum, the mop genes of Clostridium pasteurianum encoding molybdo-pterin binding proteins, and ORF3 from the A. variabilis hydrogenase gene cluster were identified within the sequenced region. For mutational analysis the Anabaena 7120 mutant strains LAK4, BMB92, and KSH10 were constructed. In LAK4 the fdxH coding region is disrupted by an interposon, whereas BMB92 is deleted for a 2799-bp NheI fragment encompassing fdxH, ORF3, mop, ORF4, and ORF5. Mutant strain KSH10 is a derivative of BMB92, complemented for fdxH but not for the other genes located further downstream. Analysis of the Nif phenotype of these mutant strains showed that FdxH is necessary for maximum nitrogenase activity and optimal growth under nitrogen-fixing conditions, but not absolutely essential for diazotrophic growth. The role of alternative electron donors for nitrogenase, which might substitute for FdxH, is discussed. Iron concentrations (1 microM Fe) sufficient to induce synthesis of the vegetative cell flavodoxin did not stimulate diazotrophic growth of the fdxH mutant strains, suggesting that FdxH was not replaced by a NifJ-flavodoxin system. Comparison of LAK4 and BMB92 indicated that one of the genes located downstream of fdxH might also play a (minor) role in nitrogen fixation.
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PMID:The heterocyst-specific fdxH gene product of the cyanobacterium Anabaena sp. PCC 7120 is important but not essential for nitrogen fixation. 907 90