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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)

The cells of Rhodospirillum rubrum and Thiocapsa roseopersicina grown in media containing glutamate and arginine, respectively, as well as under conditions of nitrogen fixation evolve H2 in the light. If the cultures were grown in media with NH4+, NO3-, urea, glutamine or asparagine, hydrogen photoevolution by the cells and acetylene reduction started after the lag-phase and proceeded at a low rate. Extracts of such cells did not display the activity of nitrogenase which could be assayed by the ATP-dependent evolution of H2 from dithionite. The data obtained confirm the fact that hydrogen photoevolution by purple bacteria involves nitrogenase whose synthesis is regulated (according to the action of glutamine) with the participation of glutamine synthetase. NH4+, glutamine and asparagine inhibit also hydrogen photoproduction by purple bacteria and acetylene photoreduction. However, they have no effect on hydrogen evolution in the dark by the cells of R. rubrum and T. roseopersicina in the presence of formiate or pyruvate, respectively, whereas carbon monoxide inhibits hydrogen production. Therefore, hydrogen production by purple bacteria in the dark must be catalyzed by hydrogenase.
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PMID:[Effect of nitrogen-containing compounds on hydrogen light emission and nitrogen fixation by purple bacteria]. 11 58

Two uptake hydrogenases were found in the obligate methanotroph Methylosinus trichosporium OB3b; one was constitutive, and a second was induced by H2. Both hydrogenases could be assayed by measuring methylene blue reduction anaerobically or by coupling their activity to nitrogenase acetylene reduction activity in vivo in an O2-dependent reaction. The H2 concentration for half-maximal activity of the inducible and constitutive hydrogenases in both assays was 0.01 and 0.5 bar (1 and 50 kPa), respectively, making it easy to distinguish these enzymes from one another both in vivo and in vitro. Hydrogen uptake was shown to be coupled to ATP synthesis in methane-starved cells. Methane, methanol, formate, succinate, and glucose all repressed the H2-mediated synthesis of the inducible hydrogenase. Furthermore, this enzyme was only expressed in N-starved cultures and was repressed by NH4+ and NO3-; synthesis of the constitutive hydrogenase was not affected by excess N in the growth medium. In nickel-free, EDTA-containing medium, the activities of these two enzymes were negligible; however, both enzyme activities appeared rapidly following the addition of nickel to the culture. Chloramphenicol, when added along with nickel, had no effect on the rapid appearance of either the constitutive or inducible activity, indicating that nickel is not required for synthesis of the hydrogenase apoproteins. These observations all suggest that these hydrogenases are nickel-containing enzymes. Finally, both hydrogenases were soluble and could be fractionated by 20% ammonium sulfate; the constitutive enzyme remained in the supernatant solution, while the inducible enzyme was precipitated under these conditions.
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PMID:Regulation of two nickel-requiring (inducible and constitutive) hydrogenases and their coupling to nitrogenase in Methylosinus trichosporium OB3b. 311 63

Campylobacter sputorum subsp. bubulus contained hydrogenase activity after growth with lactate and nitrate and after growth with hydrogen and nitrate. After growth with hydrogen and nitrate a molar growth yield (g dry cells/mol hydrogen) of 5.6 was measured. Hydrogenase and nitrate reductase were membrane-bound enzymes. In cells with high hydrogenase activity the----H+/O,----H+/NO2- and----H+/NO3- values with hydrogen as the electron donor were 3.74, 2.61 and 4.36 respectively. In cells with low hydrogenase activity these values were 2.33, -0.86 and 1.31 respectively. These values and the stoichiometry of respiration-driven proton translocation (----H+/2e = 2) led to the conclusion that hydrogenase is located at the periplasmic side of the cytoplasmic membrane. In cells with low lactate dehydrogenase activity or low hydrogenase activity the reduction of nitrate to nitrite could be separated from the reduction of nitrite to ammonia. Positive----H+/NO3- values (between 0.9 and 1.7) with lactate or hydrogen as the electron donor were measured in these cells whereas----H+/ NO2- values were negative. From this result it was concluded that nitrate reductase is located at the cytoplasmic face of the cytoplasmic membrane. The results explain the previous observation that molar growth yields with nitrate were somewhat higher than those with nitrite.
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PMID:Localization of hydrogenase and nitrate reductase in Campylobacter sputorum subsp. bubulus. 637 87

Nitrite, NO, CO, and C2H2 inhibited O2-dependent H2 uptake (H3H oxidation) in denitrifying Azospirillum brasilense Sp7 grown anaerobically on N2O or NO3-. The apparent Ki values for inhibition of O2-dependent H2 uptake were 20 microM for NO2-, 0.4 microM for NO, 28 microM for CO, and 88 microM for C2H2. These inhibitors also affected methylene blue-dependent H2 uptake, presumably by acting directly on the hydrogenase. Nitrite and NO inhibited H2 uptake irreversibly, whereas inhibition due to CO was easily reversed by repeatedly evacuating and backfilling with N2. The C2H2 inhibition was not readily reversed, partly due to difficulty in removing the last traces of this gas from solution. The NO2- inhibition of malate-dependent respiration was readily reversed by repeatedly washing the cells, in contrast to the effect of NO2- on H2-dependent respiration. These results suggest that the low hydrogenase activities observed in NO3(-)-grown cultures of A. brasilense may be due to the irreversible inhibition of hydrogenase by NO2- and NO produced by NO3- reduction.
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PMID:Hydrogenase activity in Azospirillum brasilense is inhibited by nitrite, nitric oxide, carbon monoxide, and acetylene. 638 89

Measurements with a PAM fluorometer showed that the photochemical activity of photosystem II (PS II) in sulfur-deprived Chlamydomonas reinhardtii cells (media TAP-S) decreases slowly under aerobic conditions. In a closed cultivator, when the rate of O2 photosynthetic evolution declines below the rate of respiration, the cell culture is under anaerobic conditions in which the activation of hydrogenase and the production of hydrogen take place. We found that the slow decrease in PS II activity is followed by an abrupt inactivation of PS II centers just after the onset of anaerobiosis. This fast PS II inactivation is reversed by aeration of the media and is accompanied by an increase in the fluorescence parameter Ft. Moreover, the rate of the abrupt PS II inactivation diminished after the addition into the medium of electron acceptors such as CO2 (carbonate-bicarbonate buffer), NO3- and SO4(2-) , the assimilation of which in chloroplasts requires a lot of reductants. We suggest that the PS II inactivation is due to the overreduction of the plastoquinone pool after the onset of anaerobiosis.
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PMID:[The photochemical activity of photosystem II in sulfur-deprived Chlamydomonas reinhardtii cells depends on the redox state of the quinone pool during the transition to anaerobiosis]. 1532 9

Regulation of H2 utilization, as monitored by the hydrogenase-mediated(3)H2 exchange reaction, was examined among phytoplankton communitiesin situ and populations in culture. During a 2-year study in the Chowan River, North Carolina, at least 2 major groups of phytoplankton dominated(3)H2 exchange rates. They included N2 fixing cyanobacteria and NO3 (})- utilizing genera. Utilization of(3)H2 by N2 fixers was mainly dark-mediated, whereas(3)H2 utilization associated with periods of NO3 (})- abundance revealed an increasing dependence on light. Inhibitors of N2 fixation (C2H2 and NH4 (+)) negatively affected(3)H2 utilization, substantiating previous findings that close metabolic coupling of both processes exists among N2 fixing cyanobacteria. Conversely, NO3 (})- stimulated(3)H2 utilization among N2 and non-N2 fixing genera, particularly under illuminated conditions. A variety of environmental factors were shown to control(3)H2 exchange. In addition to the nitrogen sources discussed above, dissolved O2, photosynthetically available radiation (PAR), temperature, and pH changes altered(3)H2 exchange rates. It is likely that other factors not addressed here could also affect(3)H2 exchange rates. At least 2 ecological benefits from H2 utilization in natural phytoplankton can be offered. They include the simultaneous generation of adenosine triphosphate (ATP) and consumption of O2 during the oxidation of H2 via an oxyhydrogen or "Knallgas" reaction. Both processes could help sustain phytoplankton, and particularly cyanobacterial, bloom intensity under natural conditions when O2 supersaturation is common in surface waters. H2 utilization appeared to be a general feature of natural and laboratory phytoplankton populations. The magnitudes of(3)H2 utilization rates were directly related to community biomass. Although it can be shown that utilization rates are controlled by specific environmental factors, the potential relationships between H2 utilization and phytoplankton primary production remain poorly understood.
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PMID:Environmental regulation of H2 utilization ( (3)H 2 exchange) among natural and laboratory populations of N2 and non-N 2 fixing phytoplankton. 2422 47