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1.
A mass spectrometer with a membrane inlet system was used to monitor directly gaseous components in a suspension of algae. Using labeled oxygen, we observed that during the first 20 seconds of illumination after a dark period, when no net O 2 evolution or CO 2 uptake was observed, O 2 evolution was normal but completely compensated by O 2 uptake. Similarly, when CO 2 uptake was totally or partially inhibited, O 2 evolution proceeded at a high (near maximal) rate. Under all conditions, O 2 uptake balanced that fraction of the O 2 evolution which could not be accounted for by CO 2 uptake. 相似文献
2.
The nature of the process responsible for the stationary O 2 uptake occurring in the light under saturating CO 2 concentration in Chlamydomonas reinhardii has been investigated. For this purpose, a mass spectrometer with a membrane inlet system was used to measure O 2 uptake and evolution in the algal suspension. First, we observed that the O 2 uptake rate was constant (about 0.5 micromoles of O 2 per milligram chlorophyll per minute) during a light to dark transition and was not affected by 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Salicylhydroxamic acid had no effect on O 2 uptake in the dark or in the light, but was found to have the same inhibitory effect either in the dark or in the light when added to cyanide-treated algae. The stimulation of the O 2 uptake rate due to the uncoupling effect of carbonyl cyanide m-chlorophenylhydrazone was about the same in the dark or in the light. From these results, we conclude that mitochondrial respiration is maintained during illumination and therefore is not inhibited by high ATP levels. Another conclusion is that in conditions where photorespiration is absent, no other light-dependent O 2 uptake process occurs. If Mehler reactions are involved, in Chlamydomonas, under conditions where both photosynthetic carbon oxidation and reduction cycles cannot operate (as in cyanide-treated algae), their occurrence in photosynthesizing algae either under saturating CO 2 concentration or at the CO 2 compensation point appears very unlikely. The comparison with the situation previously reported in Scenedesmus (R. J. Radmer and B. Kok 1976 Plant Physiol 58: 336-340) suggests that different O 2 uptake processes might be present in these two algal species. 相似文献
3.
Nitrogenase (EC 1.7.99.2) activity in pea ( Pisum savitum) nodules formed after infection with Rhizobium leguminosarum (lacking uptake hydrogenase) was measured as acetylene reduction, H 2 evolution in air and H 2 evolution in Ar:O 2. With detached roots the relative efficiency, calculated from acetylene reduction, showed a decrease (from 55 to below 0%) with increasing temperature. With excised nodules and isolated bacteroids similar results were obtained. However, the relative efficiency calculated from H 2 evolution in Ar:O 2 was unaffected by temperature. Measurements on both excised nodules and isolated bacteroids showed a marked difference between acetylene reduction and H 2 evolution in Ar:O 2 with increased temperature, indicating that either acetylene reduction or H 2 evolution in Ar:O 2 are inadequate measures of nitrogenase activity at higher temperature. 相似文献
4.
Oxygen inhibition of photosynthesis and CO 2 evolution during photorespiration were compared in high CO 2-grown and air-grown Chlorella pyrenoidosa, using the artificial leaf technique at pH 5.0. High CO 2 cells, in contrast to air-grown cells, exhibited a marked inhibition of photosynthesis by O 2, which appeared to be competitive and similar in magnitude to that in higher C 3 plants. With increasing time after transfer to air, the photosynthetic rate in high CO 2 cells increased while the O 2 effect declined. Photorespiration, measured as the difference between 14CO 2 and 12CO 2 uptake, was much greater and sensitive to O 2 in high CO 2 cells. Some CO 2 evolution was also present in air-grown algae; however, it did not appear to be sensitive to O 2. True photosynthesis was not affected by O 2 in either case. The data indicate that the difference between high CO 2 and air-grown algae could be attributed to the magnitude of CO 2 evolution. This conclusion is discussed with reference to the oxygenase reaction and the control of photorespiration in algae. 相似文献
5.
Peas ( Pisum sativum L.) were inoculated with strains of Rhizobium leguminosarum having different levels of uptake hydrogenase (Hup) activity and were grown in sterile Leonard jars under controlled conditions. Rates of H 2 evolution and acetylene reduction were determined for intact nodulated roots at intervals after the onset of darkness or after removal of the shoots. Hup activity was estimated using treatment plants or equivalent plants from the growth chamber, by measuring the uptake of H 2 or 3H 2 in the presence of acetylene. In all cases, the rate of H 2 evolution was a continuous function of the rate of acetylene reduction. In symbioses with no demonstrable Hup activity, H 2 evolution increased in direct proportion to acetylene reduction and the slopes were similar with the Hup − strains NA502 and 128C79. Hup activity was similar in strains 128C30 and 128C52 but significantly lower in strain 128C54. With these strains, the slopes of the H 2 evolution versus acetylene reduction curves initially increased with acetylene reduction, but became constant and similar to those for the Hup − strains at high rates of acetylene reduction. On these parallel portions of the curves, the decreases in H 2 evolution by Hup + strains were similar in magnitude to their H 2-saturated rates of Hup activity. The curvilinear relationship between H 2 evolution and acetylene reduction for a representative Hup + strain (128C52) was the same, regardless of the experimental conditions used to vary the nitrogenase activity. 相似文献
6.
A mass spectrometer with a membrane inlet was used to monitor light-driven O 2 evolution, O 2 uptake, and CO 2 uptake in suspensions of algae ( Scenedesmus obliquus). We observed the following. ( a) The rate of O 2 uptake, which, in the presence of iodoacetamide, replaces the uptake of CO 2, showed a distinct plateau (V max) beyond ~30% O 2 and was half-maximal at ~8% O 2. We concluded that this light-driven O 2 uptake process, which does not involve carbon compounds, is saturated at lower O 2 concentrations than are photorespiration and glycolate formation. ( b) In the absence of inhibitor, O 2 evolution was relatively unaffected by the presence or absence of CO 2. During the course of CO 2 depletion, electron flow to CO 2 was replaced by an equivalent flow to O 2. ( c) There was a distinct delay between the cessation of CO 2 uptake and the increase in O 2 uptake. We ascribe this delay to the transient utilization of another electron acceptor—possibly bicarbonate or another bound form of CO 2. 相似文献
7.
The H 2-oxidizing complex in Rhizobium japonicum 122 DES bacteroids failed to catalyze, at a measurable rate, 2H 1H exchange from a mixture of 2H 2 and 1H 2 in presence of 2H 2O and 1H 2O, providing no evidence for reversibility of the hydrogenase reaction in vivo. In the H 2 oxidation reaction, there was no significant discrimination between 2H 2 and 1H 2, indicating that the initial H 2-activation step in the over-all H 2 oxidation reaction is not rate-limiting. By use of improved methods, an apparent Km for H 2 of 0.05 micromolar was determined. The H 2 oxidation reaction in bacteroids was strongly inhibited by cyanide (88% at 0.05 millimolar), theonyltrifluoroacetone, and other metal-complexing agents. Carbonyl cyanide m-chlorophenylhydrazone at 0.005 millimolar and 2,4-dinitrophenol at 0.5 millimolar inhibited H 2 oxidation and stimulated O 2 uptake. This and other evidence suggest the involvement of cytochromes and nonheme iron proteins in the pathway of electron transport from H 2 to O 2. Partial pressures of H 2 at 0.03 atmosphere and below had a pronounced inhibitory effect on endogenous respiration by bacteroid suspensions. The inhibition of CO 2 evolution by low partial pressures of H 2 suggests that H 2 utilization may result in conservation of oxidizable substrates and benefits the symbiosis under physiological conditions. Succinate, acetate, and formate at concentrations of 50 millimolar inhibited rates of H 2 uptake by 8, 29, and 25%, respectively. The inhibition by succinate was noncompetitive and that by acetate and formate was uncompetitive. A concentration of 11.6 millimolar CO 2 (initial concentration) in solution inhibited H 2 uptake by bacteroid suspensions by 18%. Further research is necessary to establish the significance of the inhibition of H 2 uptake by succinate, acetate, formate, and CO 2 in the metabolism of the H 2-uptake-positive strains of Rhizobium. 相似文献
8.
The H 2 uptake activity (units/mg protein) of Clostridium pasteurianum cells with methylene blue as the electron acceptor increases with cell density independent of the growth conditions. The H 2 evolution activity (units/mg protein) of the same cells with reduced methyl viologen as the electron donor remains fairly constant under all growth conditions tested. Cells grown under N 2-fixing conditions have the highest H 2 uptake activity and were used for the purification of hydrogenase II (uptake hydrogenase). Attempts to separate hydrogenase II from hydrogenase I (bidirectional hydrogenase) by a previously published method were unreliable. We report here a new large-scale purification procedure which employs a rapid membrane filtration system to fractionate cell-free extracts. Hydrogenases I and II were easily filtered into the low-molecular-weight fraction ( Mr less than 100 000), and from this, hydrogenase II was further purified to a homogeneous state. Hydrogenase II is a monomeric iron-sulfur protein of molecular weight 53 000 containing eight iron atoms and eight acid-labile sulfur atoms per molecule. Hydrogenase II catalyzes both H 2 oxidation and H 2 evolution at rates of 3000 and 5.9 μmol H 2 consumed or evolved/min per mg protein, respectively. The purification procedure for hydrogenase II using the filtration system described greatly facilitates the large-scale purification of hydrogenase I and other enzymes from cell-free extracts of C. pasteurianum. 相似文献
9.
The unicellular cyanobacterium Chroococcidiopsis thermalis CALU 758 growing photoautotrophically synthesised a hydrogenase which catalysed an in vivo H 2 uptake in the oxyhydrogen reaction at a significant rate and showed only low level of in vitro MV-dependent H 2 evolution. The in vitro hydrogenase activity was not induced under microaerobic or nitrate-limiting conditions. Some correlation observed between the two activities indicated that the same enzyme may be involved in both H 2 uptake and H 2 evolution. Heterologous Southern hybridisations, using cyanobacterial hup and hox DNA fragments as probes, showed the presence of sequences similar to hox (encoding for a bidirectional hydrogenase) in C. thermalis CALU 758 with no indication for the presence of any sequences corresponding to an uptake hydrogenase. Further molecular experiments, using specific primers directed against different conserved regions of the large subunit ( hoxH) of the bidirectional hydrogenase confirmed the presence of corresponding sequences in C. thermalis CALU 758. Low-stringency Southern hybridisations detected only one copy of hoxH within the genome of C. thermalis CALU 758. 相似文献
10.
The brown algae Desmarestia ligulata var. ligulata (Lightf.) Lamour., and D. viridis (Mull.) Lamour., accumulate H 2SO 4 until their average internal pH is 0.5 to 0.8. A related species, D. aculeata (L.) Lamour., does not accumulate acid. The H 2SO 4 accumulation is accompanied by a reduction in the K + and Cl − content, presumedly to maintain osmotic balance. Measurements of the membrane potential and H + and SO 42− concentrations indicate that both ions are accumulated in the vacuole against their electrochemical potential gradients. The internal pH remains constant in all three species over the growing season, despite striking changes in the algal morphology. The pH is not affected by periods of darkness of up to 34 hours. Sulfate accumulated in the vacuoles appears to be trapped there since incubation of D. ligulata for up to 10 days in sulfate-free medium resulted in little loss of either vacuolar sulfate or H+. Although the uptake of H2SO4 into the vacuole must require energy, the maintenance of the vacuolar H2SO4 may be due to the impermeability of the tonoplast, with little necessity for continued expenditure of energy. 相似文献
11.
A method is described for the isolation of photosynthetically active chloroplasts from four species of brown algae: Fucus vesiculosis, Nereocystis luetkeana, Laminaria saccharina, and Macrocystis integrifolia. When compared to lettuce and spinach chloroplasts, the algal chloroplasts all showed lower activities for both photosystems II and I. Chloroplasts from all the plants produced H 2O 2, with photosystem I functioning as the O 2 reductant in the light. In contrast to the green plants, however, brown algal chloroplasts strongly reduced O 2 under conditions where both photosystems II and I remain active. Relative variable fluorescence values were lower both in intact plants and chloroplasts of the brown algae than for either spinach or lettuce. It is suggested that although light harvesting activities appear similar in all the plants, details of electron transport in brown algae may differ from those of green plants. 相似文献
12.
Escherichia coli uptake hydrogenase 2 (Hyd-2) catalyzes the reversible oxidation of H 2 to protons and electrons. Hyd-2 synthesis is strongly upregulated during growth on glycerol or on glycerol-fumarate. Membrane-associated Hyd-2 is an unusual heterotetrameric [NiFe]-hydrogenase that lacks a typical cytochrome b membrane anchor subunit, which transfers electrons to the quinone pool. Instead, Hyd-2 has an additional electron transfer subunit, termed HybA, with four predicted iron-sulfur clusters. Here, we examined the physiological role of the HybA subunit. During respiratory growth with glycerol and fumarate, Hyd-2 used menaquinone/demethylmenaquinone (MQ/DMQ) to couple hydrogen oxidation to fumarate reduction. HybA was essential for electron transfer from Hyd-2 to MQ/DMQ. H 2 evolution catalyzed by Hyd-2 during fermentation of glycerol in the presence of Casamino Acids or in a fumarate reductase-negative strain growing with glycerol-fumarate was also shown to be dependent on both HybA and MQ/DMQ. The uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP) inhibited Hyd-2-dependent H 2 evolution from glycerol, indicating the requirement for a proton gradient. In contrast, CCCP failed to inhibit H 2-coupled fumarate reduction. Although a Hyd-2 enzyme lacking HybA could not catalyze Hyd-2-dependent H 2 oxidation or H 2 evolution in whole cells, reversible H 2-dependent reduction of viologen dyes still occurred. Finally, hydrogen-dependent dye reduction by Hyd-2 was reversibly inhibited in extracts derived from cells grown in H 2 evolution mode. Our findings suggest that Hyd-2 switches between H 2-consuming and H 2-producing modes in response to the redox status of the quinone pool. Hyd-2-dependent H 2 evolution from glycerol requires reverse electron transport. 相似文献
13.
Studies of H 2 evolution by N 2 fixing systems are frequently limited by an inability to accurately measure H 2 gas concentrations of less than about 10 microliters per liter. In this study, a H 2 gas analyzer is described which is able to accurately and reproducibly detect up to 100 times lower H 2 concentrations than most thermal conductivity gas chromatographs or other conventional instruments used for the measurement of H 2 gas. This high level of sensitivity (maximum of about 0.02 microliter per liter H 2 per millivolt output) and the ability to continuously monitor H 2 concentration directly in a flowing gas stream, makes this instrument well suited for use in an open gas exchange system. Since the sensor used in the instrument was also sensitive to other combustible gases, it was necessary to demonstrate that H2 was the only combustible gas produced by the N2 fixing system being studied. When an air stream was passed through a pot containing nodulated soybean (Glycine max L.) roots, gas chromatographic analysis of the effluent gas stream revealed that H2 was the only combustible gas present. These results were supported by other studies in which no combustible gases were detected in the effluent gas stream from soybean roots nodulated with USDA 110, a Rhizobium strain which displays active uptake hydrogenase activity. 相似文献
14.
Rates of 14CO 2 fixation, O 2 evolution, and N 2 fixation (acetylene reduction) by natural populations of blue-green algae recovered from Lake Mendota were measured at frequent intervals between sunrise and sunset. Photosynthesis and N 2 fixation were depressed during midday when light intensity was greatest. As the light intensity rose, most of the algal population migrated to deeper, light-limited waters where radiation damage would be diminished. As the relative rate of N 2 fixation compared to CO 2 fixation increases with depth, it is suggested that the algae maintain balanced growth by migrating vertically via buoyancy regulation. High concentrations of dissolved O 2 in lake water may inhibit N 2 fixation by enhancing photorespiration. Several factors such as photosynthetic rate, light intensity, dissolved O 2, species composition, and vertical and horizontal migration all affect observed rates of in situ N 2 fixation. 相似文献
15.
The purpose of this research was to test the hypothesis that acclimation of the unicellular marine alga, Thalassiosira fluviatilis Hustedt, to short photoperiods results in decreased cellular concentrations of ribulose 1,5-bisphosphate carboxylase/oxygenase and decreased rates of light-saturated CO 2 uptake. Cells were acclimated to photoperiods of 6:18, 12:12, and 18:6 h:h light:dark, and concentrations of the large subunit of the enzyme and responses of CO 2 uptake to varying irradiance were measured. Concentrations of the large subunit, which weighed approximately 50 kilodaltons, were conserved while rates of CO 2 uptake under light saturation and limitation, and cellular contents of chlorophyll a increased as photoperiod decreased. Apparently, these cells acclimate to short photoperiods by increasing rates of CO 2 uptake under saturating irradiances by increasing in vivo activation of ribulose 1,5-bisphosphate carboxylase/oxygenase. Also, chlorophyll-specific concentrations and specific activities of the enzyme appear to be lower and higher, respectively, in diatomaceous algae than in higher plants. 相似文献
16.
Carbonyl sulfide (COS), a substrate for carbonic anhydrase, inhibited alkalization of the medium, O 2 evolution, dissolved inorganic carbon accumulation, and photosynthetic CO 2 fixation at pH 7 or higher by five species of unicellular green algae that had been air-adapted for forming a CO 2-concentrating process. This COS inhibition can be attributed to inhibition of external HCO 3− conversion to CO 2 and OH − by the carbonic anhydrase component of an active CO 2 pump. At a low pH of 5 to 6, COS stimulated O 2 evolution during photosynthesis by algae with low CO 2 in the media without alkalization of the media. This is attributed to some COS hydrolysis by carbonic anhydrase to CO 2. Although COS had less effect on HCO 3− accumulation at pH 9 by a HCO 3− pump in Scenedesmus, COS reduced O 2 evolution probably by inhibiting internal carbonic anhydrases. Because COS is hydrolyzed to CO 2 and H 2S, its inhibition of the CO 2 pump activity and photosynthesis is not accurate, when measured by O 2 evolution, by NaH 14CO 3 accumulation, or by 14CO 2 fixation. 相似文献
17.
Unicellular green algae have the ability to operate in two distinctly different environments (aerobic and anaerobic), and
to photosynthetically generate molecular hydrogen (H 2). A recently developed metabolic protocol in the green alga Chlamydomonas reinhardtii permitted separation of photosynthetic O 2-evolution and carbon accumulation from anaerobic consumption of cellular metabolites and concomitant photosynthetic H 2-evolution. The H 2 evolution process was induced upon sulfate nutrient deprivation of the cells, which reversibly inhibits photosystem-II and
O 2-evolution in their chloroplast. In the absence of O 2, and in order to generate ATP, green algae resorted to anaerobic photosynthetic metabolism, evolved H 2 in the light and consumed endogenous substrate. This study summarizes recent advances on green algal hydrogen metabolism
and discusses avenues of research for the further development of this method. Included is the mechanism of a substantial tenfold
starch accumulation in the cells, observed promptly upon S-deprivation, and the regulated starch and protein catabolism during
the subsequent H 2-evolution. Also discussed is the function of a chloroplast envelope-localized sulfate permease, and the photosynthesis–respiration
relationship in green algae as potential tools by which to stabilize and enhance H 2 metabolism. In addition to potential practical applications of H 2, approaches discussed in this work are beginning to address the biochemistry of anaerobic H 2 photoproduction, its genes, proteins, regulation, and communication with other metabolic pathways in microalgae. Photosynthetic
H 2 production by green algae may hold the promise of generating a renewable fuel from nature’s most plentiful resources, sunlight
and water. The process potentially concerns global warming and the question of energy supply and demand. 相似文献
18.
Light-dependent O 2 exchange was measured in intact, isolated soybean ( Glycine max. var. Williams) cells using isotopically labeled O 2 and a mass spectrometer. The dependence of O 2 exchange on O 2 and CO 2 was investigated at high light in coupled and uncoupled cells. With coupled cells at high O 2, O 2 evolution followed similar kinetics at high and low CO 2. Steady-state rates of O 2 uptake were insignificant at high CO 2, but progressively increased with decreasing CO 2. At low CO 2, steady-state rates of O 2 uptake were 50% to 70% of the maximum CO 2-supported rates of O 2 evolution. These high rates of O 2 uptake exceeded the maximum rate of O 2 reduction determined in uncoupled cells, suggesting the occurrence of another light-induced O 2-uptake process ( i.e. photorespiration). Rates of O2 exchange in uncoupled cells were half-saturated at 7% to 8% O2. Initial rates (during induction) of O2 exchange in uninhibited cells were also half-saturated at 7% to 8% O2. In contrast, steady-state rates of O2 evolution and O2 uptake (at low CO2) were half-saturated at 18% to 20% O2. O2 uptake was significantly suppressed in the presence of nitrate, suggesting that nitrate and/or nitrite can compete with O2 for photoreductant. These results suggest that two mechanisms (O2 reduction and photorespiration) are responsible for the light-dependent O2 uptake observed in uninhibited cells under CO2-limiting conditions. The relative contribution of each process to the rate of O2 uptake appears to be dependent on the O2 level. At high O2 concentrations (≥40%), photorespiration is the major O2-consuming process. At lower (ambient) O2 concentrations (≤20%), O2 reduction accounts for a significant portion of the total light-dependent O2 uptake. 相似文献
19.
Clostridium pasteurianum has two distinct hydrogenases, the bidirectional hydrogenase and the H 2-oxidizing (uptake) hydrogenase. The H 2-oxidizing hydrogenase has been purified (up to 970-fold) to a specific activity of 17,600 μmol H 2 oxidized/min·mg protein (5 mM methylene blue) or 3.5 μmol H 2 produced/min·mg protein (1 mM methyl viologen). The uptake hydrogenase has a M r of 53,000 (one polypeptide chain). Depending upon how protein was measured, the Fe and S = contents (gatom/mol) were 4.7 and 5.2 (by the dye-binding assay) or 7.2 and 8.0 (by the Lowry method). Both reduced and oxidized forms of the enzyme gave electron paramagnetic resonance signals. The activation energy for H 2-production and H 2-oxidation by the uptake hydrogenase was 59.1 and 31.2 kJ/mol, respectively. In the exponential phase of growth, the ratio of uptake hydrogenase/bidirectional hydrogenase in NH 3-grown cells was much lower than that in N 2-fixing cells. 相似文献
20.
Rates of photosynthetic O 2 evolution, for measuring K 0.5(CO 2 + HCO 3−) at pH 7, upon addition of 50 micromolar HCO 3− to air-adapted Chlamydomonas, Dunaliella, or Scenedesmus cells, were inhibited up to 90% by the addition of 1.5 to 4.0 millimolar salicylhydroxamic acid (SHAM) to the aqueous medium. The apparent K1(SHAM) for Chlamydomonas cells was about 2.5 millimolar, but due to low solubility in water effective concentrations would be lower. Salicylhydroxamic acid did not inhibit oxygen evolution or accumulation of bicarbonate by Scenedesmus cells between pH 8 to 11 or by isolated intact chloroplasts from Dunaliella. Thus, salicylhydroxamic acid appears to inhibit CO 2 uptake, whereas previous results indicate that vanadate inhibits bicarbonate uptake. These conclusions were confirmed by three test procedures with three air-adapted algae at pH 7. Salicylhydroxamic acid inhibited the cellular accumulation of dissolved inorganic carbon, the rate of photosynthetic O 2 evolution dependent on low levels of dissolved inorganic carbon (50 micromolar Na-HCO 3), and the rate of 14CO 2 fixation with 100 micromolar [ 14C] HCO 3−. Salicylhydroxamic acid inhibition of O 2 evolution and 14CO 2-fixation was reversed by higher levels of NaHCO 3. Thus, salicylhydroxamic acid inhibition was apparently not affecting steps of photosynthesis other than CO 2 accumulation. Although salicylhydroxamic acid is an inhibitor of alternative respiration in algae, it is not known whether the two processes are related. 相似文献
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