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Query: HUMANGGP:003739 (CO2)
 48,959 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.
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PMID:An energy-conserving pyruvate-to-acetate pathway in Entamoeba histolytica. Pyruvate synthase and a new acetate thiokinase. 1 76

Factors that regulate the expression of an H2 uptake system in free-living cultures of Rhizobium japonicum have been investigated. Rapid rates of H2 uptake by R. japonicum were obtained by incubation of cell suspensions in a Mg-phosphate buffer under a gas phase of 86.7% N2, 8.3% H2, 4.2% CO2, and 0.8% O2. Cultures incubated under conditions comparable with those above, with the exception that Ar replaced H2, showed no hydrogenase activity. When H2 was removed after initiation of hydrogenase derepression, further increase in hydrogenase activity ceased. Nitrogenase activity was not essential for expression of hydrogenase activity. All usable carbon substrates tested repressed hydrogenase formation, but none of them inhibited hydrogenase activity. No effect on hydrogenase formation was observed from the addition of KNO3 or NH4Cl at 10 mM. Oxygen repressed hydrogenase formation, but did not inhibit activity of the enzyme in whole cells. The addition of rifampin or chloramphenicol to derepressed cultures resulted in inhibition of enzyme formation similar to that observed by O2 repression. The removal of CO2 during derepression caused a decrease in the rate of hydrogenase formation. No direct effect of CO2 on hydrogenase activity was observed.
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PMID:Regulation of hydrogenase in Rhizobium japonicum. 42 13

Forty-four mutants of Alcaligenes eutrophus H 16 were isolated which grew poorly or not at all under autotrophic conditions. Four types were characterized with respect to their defects and their physiological properties. One mutant lacked both enzymes specific for autotrophic CO2 fixation, another one lacked both hydrogenases, and two mutants lacked either the membrane-bound or the soluble hydrogenase. Comparing the results of studies on these mutant types, the following conclusions were drawn: the lack of each hydrogenase enzyme could be partially compensated by the other one; the lack of membrane-bound hydrogenase did not affect autotrophic growth, whereas the lack of the soluble hydrogenase resulted in a decreased autotrophic growth rate. When pyruvate as well as hydrogen were supplied to the wild-type, the cell yield was higher than in the presence of pyruvate alone. Mutant experiments under these conditions indicated that either of both hydrogenases was able to add to the energy supply of the cell. Only the soluble hydrogenase was involved in the control of the rate of hydrogen oxidation by carbon dioxide; the mutant lacking this enzyme did not respond to the presence or absence of CO2. The suppression of growth on fructose by hydrogen could be mediated by either of both hydrogenases alone.
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PMID:Mutants of Alcaligenes eutrophus defective in autotrophic metabolism. 67 18

From enrichment cultures four carbon monoxide utilizing bacteria were isolated; strain OM5 isolated from waste water was studied in detail. The cells are Gram-negative, slightly curved rods, motile by a single subpolarly inserted flagellum. The colonies are smooth, translucent and not slimy. The cells are able to grow autotrophically in mineral medium under an atmosphere of 40% CO, 5% O2 and 55% N2 at a doubling time of 20h (30 degrees C) or of 85% H2, 5% O2 and 10% CO2 at a doubling time of 7h. Heterotrophic growth occurred on organic acids such as acetate(td = 8h), pyruvate(td = 8h), lactate, crotonate, malate, succinate (td = 8h), formate (td = 35h) and glyoxylate as substrates. The enzyme system for carbon monoxide utilization is formed only during growth on CO; hydrogenase is present in cells grown on CO or on H2 + CO2 as well as grown on pyruvate. The rate of oxygen reduction by intact CO-grown cells is 3.7-fold higher in the presence of hydrogen than in the presence of carbon monoxide. During growth the stoichiometry of gas uptake was 6.1 CO + 2.8 O2 + H2O leads to CH2O +5.1 CO2. For the new isolate the name Pseudomonas carboxydovorans (Kistner) comb. nov. has been proposed.
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PMID:Reisolation of the carbon monoxide utilizing hydrogen bacterium Pseudomonas carboxydovorans (Kistner) comb. nov. 69 1

The products of glucose fermentation were studied in 87 strains of the genus Chlorella. Lactic acid, acetic acid, formic acid, glycerol, ethanol, H2 and CO2 were identified. The lactic acid was shown to be D(minus)lactic acid. The pattern of fermentation produces is species-specific and can therefore be used as a taxonomic character. Lactic acid was found in C. fusca (varieties vacuolata, fusca, and rubescens), C. zofingiensis, C. vulgaris (var. vulgaris and f.tertia), and C. protothecoides. Formic acid and H2 appeared in those species which contain hydrogenase. Rather large amounts of glycerol were produced only by the most salt-tolerant species C. luteoviridis, C. saccharophila, and C. protothecoides.
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PMID:Physiological and biochemical contributions to the taxonomy of the genus Chlorella. X. Products of glucose fermentation. 115 86

The cells of Pseudomonas methylica, strain 2, cultivated in a medium containing methanol, displayed the activity of hydrogenase in the exchange reaction (D2--H2O) and in the absorption of H2 in the presence of methylviologen, azocarmine, methylene blue, and ferricyanide. The rate of H2 utilization was highest in the presence of methylviologen. Cell extracts absorb H2 in the presence of methylviologen, NAD, and NADP, but much faster in the presence of flavin mononucleotide. The bulk of the hydrogenase remains, during centrifugation of the initial cell extract (3,000 g), in the soluble fraction (144,000 g). The absorption of oxygen by the cell suspensions and the incorporation of 14C of formiate into the cells are stimulated by H2. The cells, however, cannot grow in the autotrophic conditions at the account of molecular hydrogen and CO2.
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PMID:[Hydrogenase activity of the methylotroph, Pseudomonas methylica]. 120 95

Mutations in the genes coding for the soluble and the membrane-bound hydrogenase of Alcaligenes eutrophus strain H16 significantly affected the expression of respiratory chain components. In lithoautotrophically grown wild type cells electron flow mainly proceeded via the cytochrome c oxidases. Mutants defective in the membrane-bound hydrogenase contained a 2- to 3-fold higher cytochrome a content than the wild type and cytochrome c oxidase of the aa3-type was preferentially used by these cells for substrate oxidation. Mutants impaired in the soluble hydrogenase revealed slow growth on hydrogen, presumably due to inefficient reverse electron flow mechanisms which provide the cells with NADH for autotrophic CO2-fixation. In this class of mutants the two quinol oxidases of the o- and d-type in addition to the co-type oxidase were the predominant electron-transport branches.
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PMID:Hydrogenase mutants of Alcaligenes eutrophus H16 show alterations in the electron transport system. 139 34

The microaerophilic protozoon Trichomonas vaginals responds to extracellular changes in oxygen concentration: acetate, lactate, ethanol, H2 and CO2 formation, as well as glucose-depletion rates, are affected. All these variables except ethanol production rates, also differed between clinically metronidazole-sensitive (1910) and resistant (IR78 and CDC85) strains. Most interesting were the greatly increased glucose-scavenging rates of resistant isolates and their low specific activities of hydrogenase and H2 formation rates by comparison with the metronidazole-sensitive strain. Results suggest that all three strains of this parasite are well adapted to the O2 levels prevailing in situ (13-56 microM). Thus, vaginal oxygen tensions have more pronounced effects on the balances of fermentation products in the resistant strains, and results indicate that these strains may then use hydrogenosomal pathways to their advantage.
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PMID:Influence of oxygen on the fermentative metabolism of metronidazole-sensitive and resistant strains of Trichomonas vaginalis. 147 4

Both Clostridium formicoaceticum and Clostridium aceticum grew chemolithoautotrophically on carbon monoxide plus CO2 in defined medium in the absence of carbohydrates, amino acids, or other carbon and energy sources. Formate supported the growth of both organisms as well in both defined and undefined media (both of which also contained CO2). Hydrogen was stimulatory to the growth of C. formicoaceticum upon first transfer into H2-enriched formate medium; however, neither chemolithoautotrophic growth at the expense of H2 plus CO2 nor hydrogenase could be demonstrated with this acetogen. Consistent with recent findings with other acetogens, numerous aromatic compounds were utilized by C. aceticum and C. formicoaceticum: (i) aromatic methoxyl groups were O-demethylated; (ii) aromatic acrylates were reduced; and (iii) aromatic aldehydes were oxidized. These findings demonstrate that the metabolic potentials of these two acetogens are greater than previously recognized.
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PMID:Re-examination of the metabolic potentials of the acetogens Clostridium aceticum and Clostridium formicoaceticum: chemolithoautotrophic and aromatic-dependent growth. 151 7

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.
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PMID:Glucose catabolism by Spirochaeta thermophila RI 19.B1. 155 64


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