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

---

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

Under anaerobic conditions, cells of Entamoeba histolytica grown with bacteria produce H2 and acetate while cells grown axenically produce neither. Aerobically, acetate is produced and O2 is consumed by amebae from either type of cells. Centrifuged extracts, 2.4 x 106 x g x min, from both types of cells contain pyruvate synthase (EC 1.2.7.1) and an acetate thiokinase which, together, form a system capable of converting pyruvate to acetate. Pyruvate synthase catalyzes the reaction: pyruvate + CoA leads to CO2 + acetyl-CoA + 2E. Electron acceptors which function with this enzyme are FAD, FMN, riboflavin, ferredoxin, and methyl viologen, but not NAD or NADP. The amebal acetate thiokinase catalyzes the reaction acetyl-CoA + ADP + Pi leads to acetate + ATP + CoA. For this apparently new enzyme we suggest the trivial name acetyl-CoA-synthetase (ADP-forming). Extracts from axenic amebae do not contain hydrogenase, but extracts from cells grown with bacteria do. It is postulated that in bacteria-grown amebae electrons generated at the pyruvate synthase step are utilized anaerobically to produce H2 via the hydrogenase and that the acetyl-CoA is converted to acetate in an energy-conserving step catalyzed by amebal acetyl-CoA synthetase. Aerobically, cells grown under either regimen may utilize the energy-conserving pyruvate-to-acetate pathway since O2 then serves as the ultimate electron acceptor.
...
PMID:An energy-conserving pyruvate-to-acetate pathway in Entamoeba histolytica. Pyruvate synthase and a new acetate thiokinase. 1 76

Cell-free extracts of Methanobacterium thermoautotrophicum were found to contain high activities of the following oxidoreductases (at 60 degrees C): pyruvate dehydrogenase (coenzyme A acetylating), 275 nmol/min per mg of protein; alpha-ketoglutarate dehydrogenase (coenzyme A acylating), 100 nmol/min per mg; fumarate reductase, 360 nmol/min per mg; malate dehydrogenase, 240 nmol/min per mg; and glyceraldehyde-3-phosphate dehydrogenase, 100 nmol/min per mg. The kinetic properties (apparent V(max) and K(M) values), pH optimum, temperature dependence of the rate, and specificity for electron acceptors/donors of the different oxidoreductases were examined. Pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase were shown to be two separate enzymes specific for factor 420 rather than for nicotinamide adenine dinucleotide (NAD), NADP, or ferredoxin as the electron acceptor. Both activities catalyzed the reduction of methyl viologen with the respective alpha-ketoacid and a coenzyme A-dependent exchange between the carboxyl group of the alpha-ketoacid and CO(2). The data indicate that the two enzymes are similar to pyruvate synthase and alpha-ketoglutarate synthase, respectively. Fumarate reductase was found in the soluble cell fraction. This enzyme activity coupled with reduced benzyl viologen as the electron donor, but reduced factor 420, NADH, or NADPH was not effective. The cells did not contain menaquinone, thus excluding this compound as the physiological electron donor for fumarate reduction. NAD was the preferred coenzyme for malate dehydrogenase, whereas NADP was preferred for glyceraldehyde-3-phosphate dehydrogenase. The organism also possessed a factor 420-dependent hydrogenase and a factor 420-linked NADP reductase. The involvement of the described oxidoreductases in cell carbon synthesis is discussed.
...
PMID:Oxidoreductases involved in cell carbon synthesis of Methanobacterium thermoautotrophicum. 91 79

Spirochaeta thermophila RI 19.B1 (DSM 6192) fermented glucose to lactate, acetate, CO2, and H2 with concomitant formation of cell material. The cell dry mass yield was 20.0 g/mol of glucose. From the fermentation balance data and knowledge of the fermentation pathway, a YATP of 9.22 g of dry mass per mol of ATP was calculated for pH-uncontrolled batch-culture growth on glucose in a mineral medium. Measurement of enzyme activities in glucose-grown cells revealed that glucose was taken up by a permease and then subjected to ATP-dependent phosphorylation by a hexokinase. Glucose-6-phosphate was further metabolized to pyruvate through the Embden-Meyerhof-Parnas pathway. The phosphoryl donor for phosphofructokinase activity was PPi rather than ATP. This was also found for the type strain of S. thermophila, Z-1203 (DSM 6578). PPi was probably formed by pyrophosphoroclastic cleavage of ATP, with recovery of the resultant AMP by the activity of adenylate kinase. All other measured kinase activities utilized ATP as the phosphoryl donor. Pyruvate was further metabolized to acetyl coenzyme A with concomitant production of H2 and CO2 by pyruvate synthase. Lactate was also produced from pyruvate by a fructose-1,6-diphosphate-insensitive lactate dehydrogenase. Evidence was obtained for the transfer of reducing equivalents from the glycolytic pathway to hydrogenase to produce H2. No formate dehydrogenase or significant ethanol-producing enzyme activities were detected.
...
PMID:Glucose catabolism by Spirochaeta thermophila RI 19.B1. 155 64

The effects of O2 and CO2 on the growth in culture of Trichomonas vaginalis strain C1-NIH were investigated. Growth under pre-purified N2 in the absence of CO2 supplementation gave a doubling time of 4.4 h; when traces of O2 (less than 0.25 microM) were present, the doubling time was 3.5 h. Organisms grew most rapidly (doubling time 2.3 h) with traces of O2 (less than 0.25 microM) and with the CO2 level controlled at 5 mM. The balance of fermentation products from maltose was greatly influenced by supplied gases. Under strictly anaerobic conditions at 5 mM CO2, equimolar glycerol and lactate accounted for more than 95% of the measured products, whereas lower CO2 increased acetate production. Under microaerobic conditions (O2 less than 0.25 microM) acetate was the major product when CO2 was limited to that evolved endogenously; again 5 mM CO2 favoured glycerol and lactate production. Activities of key enzymes measured in cell-free extracts (pyruvate:ferredoxin oxidoreductase, hydrogenase, glycerol kinase, malate dehydrogenase (decarboxylating) and lactate dehydrogenase) altered with growth conditions commensurately with observed changes in metabolic flux patterns. These results suggest that T. vaginalis is optimally adapted to conditions it experiences in situ in the vagina (traces of O2, high CO2).
...
PMID:Trichomonas vaginalis requires traces of oxygen and high concentrations of carbon dioxide for optimal growth. 211 56

The rumen entodiniomorphid ciliate protozoon Polyplastron multivesiculatum was shown, by biochemical and electron microscopic techniques, to possess hydrogenosomes. After differential centrifugation of whole cell homogenates the hydrogenosomal marker enzymes pyruvate:ferredoxin oxidoreductase and hydrogenase were recovered predominantly (61% and 70% of activity respectively) in the large granular fractions that were sedimented by centrifugation for 10(4) g-min (fraction P1) and 10(5) g-min (fraction P2). These subcellular fractions contained membrane-bound organelles that were approximately 0.4-0.6 microns in diameter and which had a mean equilibrium density of 1.22-1.24 g ml-1 after isopycnic centrifugation in sucrose gradients. Malate dehydrogenase (decarboxylating) activity, however, was predominantly non-sedimentable after centrifugation for 6 x 10(6) g-min. Numerous hydrogenosome-like organelles were present in the ectoplasm and endoplasm of the cell. Hydrogenase activity was demonstrated and localized in the protozoan cell using a novel staining procedure with distyryl nitroblue tetrazolium chloride (DSNBT).
...
PMID:Hydrogenosomes in the rumen entodiniomorphid ciliate Polyplastron multivesiculatum. 212 8

1. The activities of pyruvate:methyl viologen oxidoreductase (EC 1.2.7.1), hydrogenase (EC 1.18.99.1), NADH:methyl viologen oxidoreductase (EC 1.6.99.3), NADPH:methyl viologen oxidoreductase (EC 1.6.99.1), NADH oxidase (EC 1.6.99.3) and NADPH oxidase (EC 1.6.99.1) were determined for Trichomonas vaginalis, Tritrichomonas foetus and Trichomitus batrachorum. 2. The three trichomonad species were found to differ significantly, especially with respect to NADH oxidase and NADH:methyl viologen oxidoreductase activities. 3. The species differences in ferredoxin-linked and oxygen-metabolising enzymes may be related to the ways in which the trichomonads are adapted for growth in their respective hosts.
...
PMID:Comparative study of ferredoxin-linked and oxygen-metabolizing enzymes of trichomonads. 349 72

Sedimentable hydrogenase activity was demonstrated in cell-free extracts from both zoospores and vegetative growth of the anaerobic rumen fungus Neocallimastix patriciarum. Electron micrographs of the fraction enriched in hydrogenase activity contained finely granular microbody-like organelles, about 0.5 micron in diameter and having an equilibrium density of about 1.2 g X ml-1 in sucrose, 1.12 g X ml-1 in Percoll and 1.27-1.28 g X ml-1 in Metrizamide. These organelles, which are sedimentable at 10(5) g-min, bear no similarity to mitochondria, but are morphologically similar to hydrogen-evolving organelles possessed by certain anaerobic protozoa and termed 'hydrogenosomes'. Other typical hydrogenosomal enzymes, namely 'malic' enzyme, pyruvate:ferredoxin oxidoreductase and NADPH:ferredoxin oxidoreductase, were enriched in the same particle fraction as hydrogenase. The synthesis of pyruvate:ferredoxin oxidoreductase was found to be suppressed when the organism was cultured under an atmosphere of CO2, and an alternative pathway is proposed for growth under these conditions.
...
PMID:Hydrogenosomes in the rumen fungus Neocallimastix patriciarum. 353 4

Cells of the aerotolerant anaerobe Giardia lamblia respire in the presence of oxygen. Endogenous respiration is stimulated by glucose but not by other carbohydrates and Krebs cycle intermediates. Endogenous and glucose-stimulated respiration are insensitive to cyanide, malonate, and 2,4-dinitrophenol, but are inhibited by atabrin and iodoacetamide. G. lamblia produces ethanol, acetate and CO2 both aerobically and anaerobically either from endogenous reserves or exogenous glucose. Molecular hydrogen is not produced. The following enzyme activities were detected in homogenates: hexokinase, fructose-biphosphate aldolase, pyruvate kinase, phosphoenolpyruvate carboxykinase, malate dehydrogenase, malate dehydrogenase (decarboxylating), pyruvate synthase, acetyl-CoA synthetase, alcohol dehydrogenase (NADP+), NADH dehydrogenase, NADPH dehydrogenase, NADPH oxidoreductase and superoxide dismutase. The enzymes of energy and carbohydrate metabolism are nonsedimentable (109 000 x g for 30 min). Activities of lactate dehydrogenase, hydrogenase, phosphate acetyltransferase, acetate kinase, citrate synthase, succinate dehydrogenase, fumarate hydratase and catalase were below the limits of detection. The results suggest the occurrence of glycolysis, energy production by substrate level phosphorylation and a flavin, iron-sulfur protein mediated electron transport system as well as the absence of cytochrome mediated oxidative phosphorylation and functional Krebs cycle.
...
PMID:Energy metabolism of the anaerobic protozoon Giardia lamblia. 610 7

A low molecular weight iron-sulfur protein has been purified from Tritrichomonas foetus by deoxycholate extraction of whole cells, ion exchange chromatography, and gel filtration. The purified protein was essentially homogeneous as judged by isoelectric focusing, polyacrylamide gel electrophoresis, and gel filtration. A pI of 4.3 was observed. The molecular weight of the protein was estimated to be 12,000. Chemical and spectral analysis showed the protein to have a [2Fe-2S] cluster. The absorbance spectrum of the oxidized protein showed maxima at 280, 340, 458 and shoulders at 410 and 550 nm. The maximum observed A458/A280 ratio was 0.82 and the absorbance of the oxidized protein at 458 nm was 8,000 M-1 X cm-1. The low temperature EPR spectrum of the protein reduced with dithionite revealed axial symmetry with features at g values of g = 1.94 and g = 2.02. The oxidized protein gave no EPR signal in the g = 1.8 to 2.2 range. Cell fractionation studies indicated the localization of this protein in the hydrogenosome. The protein was able to function as an electron transport component in the reduction of metronidazole (a 5-nitroimidazole derivative) by pyruvate:ferredoxin oxidoreductase and hydrogenase from T. foetus and also from Trichomonas vaginalis and Clostridium pasteurianum as well as in the reduction of cytochrome c by plant NADPH:ferredoxin oxidoreductase. This protein has the characteristics of a ferredoxin and is likely to be a physiological electron carrier in hydrogenosomal pyruvate oxidation.
...
PMID:Hydrogenosomal ferredoxin of the anaerobic protozoon, Tritrichomonas foetus. 631 59

Tritrichomonas foetus mutants resistant to metronidazole lack the hydrogenosomal enzymes pyruvate: ferredoxin oxidoreductase and hydrogenase. Hydrogenosomes of these organisms did not oxidize pyruvate or produce ATP in its presence. Elimination of hydrogenosomal metabolism of pyruvate was compensated by an increased rate of glycolysis. The resistant mutants excreted no organic acids and H2 as metabolic end products. Glycolysis of the resistant T. foetus KV1-1MR-100 can be summarized as 1 mol glucose----2 mol ethanol + 2 mol CO2. The parent strain KV1, excreting H2, CO2 and acidic end products, converted about 10% of glucose to ethanol. Both strains produced ethanol from pyruvate through the action of two cytoplasmic enzymes: pyruvate decarboxylase and alcohol dehydrogenase. The specific activity of the former enzyme, catalyzing nonoxidative decarboxylation of pyruvate to acetaldehyde, was nearly seven times higher in the resistant than in the parent strain. Alcohol dehydrogenase reducing acetaldehyde to ethanol was specific to NADPH; it catalyzed the reverse reaction only slowly, and displayed similar activities in both resistant and sensitive trichomonads. Development of anaerobic metronidazole resistance in T. foetus depended on the loss of pyruvate:ferredoxin oxidoreductase as well as on the ability to increase alcoholic fermentation.
...
PMID:Metabolic differences between metronidazole resistant and susceptible strains of Tritrichomonas foetus. 637 46


1 2 3 4 5 Next >>

---