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1.
Transition from Anoxygenic to Oxygenic Photosynthesis in a Microcoleus chthonoplastes Cyanobacterial Mat 总被引:4,自引:4,他引:0
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Benthic cyanobacterial mats with the filamentous Microcoleus chthonoplastes as the dominant phototroph grow in oxic hypersaline environments such as Solar Lake, Sinai. The cyanobacteria are in situ exposed to chemical variations between 200 μmol of sulfide liter−1 at night and 1 atm pO2 during the day. During experimental H2S to O2 transitions the microbial community was shown to shift from anoxygenic photosynthesis, with H2S as the electron donor, to oxygenic photosynthesis. Microcoleus filaments could carry out both types of photosynthesis concurrently. Anoxygenic photosynthesis dominated at high sulfide levels, 500 μmol liter−1, while the oxygenic reaction became dominant when the sulfide level was reduced below 100 to 300 μmol liter−1 (25 to 75 μmol of H2S liter−1). An increasing inhibition of the oxygenic photosynthesis was observed upon transition to oxic conditions from increasing sulfide concentrations. Oxygen built up within the Microcoleus layer of the mat even under 5 mmol of sulfide liter−1 (500 μmol of H2S liter−1) in the overlying water. The implications of such a localized O2 production in a highly reducing environment are discussed in relation to the evolution of oxygenic photosynthesis during the Proterozoic era. 相似文献
2.
Tributyltin in the concentration range 1–4μm failed to stimulate Ca2+ transport by Lucilia flight-muscle mitochondria in a medium containing KCl and respiratory substrate but devoid of Pi, despite its promotion of a rapid Cl−/OH− exchange. When 2mm-Pi was present, concentrations of tributyltin greater than 1μm inhibited the initial rate of Ca2+ transport and induced efflux of the ion from the mitochondria in Cl−- or NO3−-containing media. Lower concentrations had little effect. Oligomycin added at up to 10μg/mg of mitochondrial protein had no effect on Ca2+ transport. By contrast, approx. 0.3μm-tributyltin completely inhibited respiration supported by α-glycerophosphate in either the presence or absence of added ADP. The data suggest that tributyltin can inhibit Ca2+ transport in Lucilia flight-muscle mitochondria other than by facilitating a Cl−/OH− exchange or producing an oligomycin-like effect. 相似文献
3.
When supplied under low chloride concentrations, vanadate inhibits the blue light-stimulated swelling of Vicia faba L. guard cell protoplasts in a dose-dependent fashion. The volume of guard cell protoplasts incubated in 10 mm K-imino-diacetic acid, 0.4 m mannitol, and 1 mm CaCl2 remained essentially constant under 1000 μmol m−2 s−1 red light, but increased an average of 27% after 8 min of the addition of 50 μmol m−2 s−1 blue light to the background red light. At 500 μm, vanadate completely inhibits the response to blue light. Vanadate also inhibits the swelling of guard cell protoplasts stimulated by the H+-ATPase agonist fusicoccin. The vanadate sensitivity of the blue light-stimulated swelling implicates a proton-pumping ATPase as a component of the sensory transduction of blue light in guard cells. 相似文献
4.
Colorless Sulfur Bacteria, Beggiatoa spp. and Thiovulum spp., in O2 and H2S Microgradients 总被引:9,自引:8,他引:1
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The interactions between colorless sulfur bacteria and the chemical microgradients at the oxygen-sulfide interface were studied in Beggiatoa mats from marine sediments and in Thiovulum veils developing above the sediments. The gradients of O2, H2S, and pH were measured by microelectrodes at depth increments of 50 μm. An unstirred boundary layer in the water surrounding the mats and veils prevented microturbulent or convective mixing of O2 and H2S. The two substrates reached the bacteria only by molecular diffusion through the boundary layer. The bacteria lived as microaerophiles or anaerobes even under stirred, oxic water. Oxygen and sulfide zones overlapped by 50 μm in the bacterial layers. Both compounds had concentrations in the range of 0 to 10 μmol liter−1 and residence times of 0.1 to 0.6 s in the overlapping zone. The sulfide oxidation was purely biological. Diffusion calculations showed that formation of mats on solid substrates or of veils in the water represented optimal strategies for the bacteria to achieve a stable microenvironment, a high substrate supply, and an efficient competition with chemical sulfide oxidation. The continuous gliding movement of Beggiatoa cells in mats or the flickering motion of Thiovulum cells in veils were important for the availability of both O2 and H2S for the individual bacteria. 相似文献
5.
Hydrogen Metabolism by Decomposing Cyanobacterial Aggregates in Big Soda Lake, Nevada 总被引:5,自引:3,他引:2
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Ronald S. Oremland 《Applied microbiology》1983,45(5):1519-1525
Hydrogen production by incubated cyanobacterial epiphytes occurred only in the dark, was stimulated by C2H2, and was inhibited by O2. Addition of NO3− inhibited dark, anaerobic H2 production, whereas the addition of NH4+ inhibited N2 fixation (C2H2 reduction) but not dark H2 production. Aerobically incubated cyanobacterial aggregates consumed H2, but light-incubated rates (3.6 μmol of H2 g−1 h−1) were statistically equivalent to dark uptake rates (4.8 μmol of H2 g−1 h−1), which were statistically equivalent to dark, anaerobic production rates (2.5 to 10 μmol of H2 g−1 h−1). Production rates of H2 were fourfold higher for aggregates in a more advanced stage of decomposition. Enrichment cultures of H2-producing fermentative bacteria were recovered from freshly harvested, H2-producing cyanobacterial aggregates. Hydrogen production in these cyanobacterial communities appears to be caused by the resident bacterial flora and not by the cyanobacteria. In situ areal estimates of dark H2 production by submerged epiphytes (6.8 μmol of H2 m−2 h−1) were much lower than rates of light-driven N2 fixation by the epiphytic cyanobacteria (310 μmol of C2H4 m−2 h−1). 相似文献
6.
Clayton D. Albracht Katherine C. Rank Steven Obrzut Ivan Rayment Susan P. Gilbert 《The Journal of biological chemistry》2014,289(40):27836-27848
KIF3AB is an N-terminal processive kinesin-2 family member best known for its role in intraflagellar transport. There has been significant interest in KIF3AB in defining the key principles that underlie the processivity of KIF3AB in comparison with homodimeric processive kinesins. To define the ATPase mechanism and coordination of KIF3A and KIF3B stepping, a presteady-state kinetic analysis was pursued. For these studies, a truncated murine KIF3AB was generated. The results presented show that microtubule association was fast at 5.7 μm−1 s−1, followed by rate-limiting ADP release at 12.8 s−1. ATP binding at 7.5 μm−1 s−1 was followed by an ATP-promoted isomerization at 84 s−1 to form the intermediate poised for ATP hydrolysis, which then occurred at 33 s−1. ATP hydrolysis was required for dissociation of the microtubule·KIF3AB complex, which was observed at 22 s−1. The dissociation step showed an apparent affinity for ATP that was very weak (K½,ATP at 133 μm). Moreover, the linear fit of the initial ATP concentration dependence of the dissociation kinetics revealed an apparent second-order rate constant at 0.09 μm−1 s−1, which is inconsistent with fast ATP binding at 7.5 μm−1 s−1 and a Kd,ATP at 6.1 μm. These results suggest that ATP binding per se cannot account for the apparent weak K½,ATP at 133 μm. The steady-state ATPase Km,ATP, as well as the dissociation kinetics, reveal an unusual property of KIF3AB that is not yet well understood and also suggests that the mechanochemistry of KIF3AB is tuned somewhat differently from homodimeric processive kinesins. 相似文献
7.
James J. Matsuda Mohammed S. Filali Jessica G. Moreland Francis J. Miller Fred S. Lamb 《The Journal of biological chemistry》2010,285(30):22864-22873
ClC-3 is a Cl−/H+ antiporter required for cytokine-induced intraendosomal reactive oxygen species (ROS) generation by Nox1. ClC-3 current is distinct from the swelling-activated chloride current (IClswell), but overexpression of ClC-3 can activate currents that resemble IClswell. Because H2O2 activates IClswell directly, we hypothesized that ClC-3-dependent, endosomal ROS production activates IClswell. Whole-cell perforated patch clamp methods were used to record Cl− currents in cultured aortic vascular smooth muscle cells from wild type (WT) and ClC-3 null mice. Under isotonic conditions, tumor necrosis factor-α (TNF-α) (10 ng/ml) activated outwardly rectifying Cl− currents with time-dependent inactivation in WT but not ClC-3 null cells. Inhibition by tamoxifen (10 μm) and by hypertonicity (340 mosm) identified them as IClswell. IClswell was also activated by H2O2 (500 μm), and the effect of TNF-α was completely inhibited by polyethylene glycol-catalase. ClC-3 expression induced IClswell in ClC-3 null cells in the absence of swelling or TNF-α, and this effect was also blocked by catalase. IClswell activation by hypotonicity (240 mosm) was only partially inhibited by catalase, and the size of these currents did not differ between WT and ClC-3 null cells. Disruption of endosome trafficking with either mutant Rab5 (S34N) or Rab11 (S25N) inhibited TNF-α-mediated activation of IClswell. Thrombin also activates ROS production by Nox1 but not in endosomes. Thrombin caused H2O2-dependent activation of IClswell, but this effect was not ClC-3- or Rab5-dependent. Thus, activation of IClswell by TNF-α requires ClC-3-dependent endosomal H2O2 production. This demonstrates a functional link between two distinct anion currents, ClC-3 and IClswell. 相似文献
8.
Transient receptor potential melastatin 2 (TRPM2) is a Ca2+-permeable cation channel involved in physiological and pathophysiological processes linked to oxidative stress. TRPM2 channels are co-activated by intracellular Ca2+ and ADP-ribose (ADPR) but also modulated in intact cells by several additional factors. Superfusion of TRPM2-expressing cells with H2O2 or intracellular dialysis of cyclic ADPR (cADPR) or nicotinic acid adenine dinucleotide phosphate (NAADP) activates, whereas dialysis of AMP inhibits, TRPM2 whole-cell currents. Additionally, H2O2, cADPR, and NAADP enhance ADPR sensitivity of TRPM2 currents in intact cells. Because in whole-cell recordings the entire cellular machinery for nucleotide and Ca2+ homeostasis is intact, modulators might affect TRPM2 activity either directly, by binding to TRPM2, or indirectly, by altering the local concentrations of the primary ligands ADPR and Ca2+. To identify direct modulators of TRPM2, we have studied the effects of H2O2, AMP, cADPR, NAADP, and nicotinic acid adenine dinucleotide in inside-out patches from Xenopus oocytes expressing human TRPM2, by directly exposing the cytosolic faces of the patches to these compounds. H2O2 (1 mm) and enzymatically purified cADPR (10 μm) failed to activate, whereas AMP (200 μm) failed to inhibit TRPM2 currents. NAADP was a partial agonist (maximal efficacy, ∼50%), and nicotinic acid adenine dinucleotide was a full agonist, but both had very low affinities (K0.5 = 104 and 35 μm). H2O2, cADPR, and NAADP did not enhance activation by ADPR. Considering intracellular concentrations of these compounds, none of them are likely to directly affect the TRPM2 channel protein in a physiological context. 相似文献
9.
Distribution of Sulfate-Reducing and Methanogenic Bacteria in Anaerobic Aggregates Determined by Microsensor and Molecular Analyses 总被引:7,自引:5,他引:2
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Cecilia M. Santegoeds Lars Riis Damgaard Gijs Hesselink Jakob Zopfi Piet Lens Gerard Muyzer Dirk de Beer 《Applied microbiology》1999,65(10):4618-4629
Using molecular techniques and microsensors for H2S and CH4, we studied the population structure of and the activity distribution in anaerobic aggregates. The aggregates originated from three different types of reactors: a methanogenic reactor, a methanogenic-sulfidogenic reactor, and a sulfidogenic reactor. Microsensor measurements in methanogenic-sulfidogenic aggregates revealed that the activity of sulfate-reducing bacteria (2 to 3 mmol of S2− m−3 s−1 or 2 × 10−9 mmol s−1 per aggregate) was located in a surface layer of 50 to 100 μm thick. The sulfidogenic aggregates contained a wider sulfate-reducing zone (the first 200 to 300 μm from the aggregate surface) with a higher activity (1 to 6 mmol of S2− m−3 s−1 or 7 × 10−9 mol s−1 per aggregate). The methanogenic aggregates did not show significant sulfate-reducing activity. Methanogenic activity in the methanogenic-sulfidogenic aggregates (1 to 2 mmol of CH4 m−3 s−1 or 10−9 mmol s−1 per aggregate) and the methanogenic aggregates (2 to 4 mmol of CH4 m−3 s−1 or 5 × 10−9 mmol s−1 per aggregate) was located more inward, starting at ca. 100 μm from the aggregate surface. The methanogenic activity was not affected by 10 mM sulfate during a 1-day incubation. The sulfidogenic and methanogenic activities were independent of the type of electron donor (acetate, propionate, ethanol, or H2), but the substrates were metabolized in different zones. The localization of the populations corresponded to the microsensor data. A distinct layered structure was found in the methanogenic-sulfidogenic aggregates, with sulfate-reducing bacteria in the outer 50 to 100 μm, methanogens in the inner part, and Eubacteria spp. (partly syntrophic bacteria) filling the gap between sulfate-reducing and methanogenic bacteria. In methanogenic aggregates, few sulfate-reducing bacteria were detected, while methanogens were found in the core. In the sulfidogenic aggregates, sulfate-reducing bacteria were present in the outer 300 μm, and methanogens were distributed over the inner part in clusters with syntrophic bacteria. 相似文献
10.
Neeliyath A. Ramakrishnan Marian J. Drescher Barbara J. Morley Philip M. Kelley Dennis G. Drescher 《The Journal of biological chemistry》2014,289(13):8750-8766
Mutations in otoferlin, a C2 domain-containing ferlin family protein, cause non-syndromic hearing loss in humans (DFNB9 deafness). Furthermore, transmitter secretion of cochlear inner hair cells is compromised in mice lacking otoferlin. In the present study, we show that the C2F domain of otoferlin directly binds calcium (KD = 267 μm) with diminished binding in a pachanga (D1767G) C2F mouse mutation. Calcium was found to differentially regulate binding of otoferlin C2 domains to target SNARE (t-SNARE) proteins and phospholipids. C2D–F domains interact with the syntaxin-1 t-SNARE motif with maximum binding within the range of 20–50 μm Ca2+. At 20 μm Ca2+, the dissociation rate was substantially lower, indicating increased binding (KD = ∼10−9) compared with 0 μm Ca2+ (KD = ∼10−8), suggesting a calcium-mediated stabilization of the C2 domain·t-SNARE complex. C2A and C2B interactions with t-SNAREs were insensitive to calcium. The C2F domain directly binds the t-SNARE SNAP-25 maximally at 100 μm and with reduction at 0 μm Ca2+, a pattern repeated for C2F domain interactions with phosphatidylinositol 4,5-bisphosphate. In contrast, C2F did not bind the vesicle SNARE protein synaptobrevin-1 (VAMP-1). Moreover, an antibody targeting otoferlin immunoprecipitated syntaxin-1 and SNAP-25 but not synaptobrevin-1. As opposed to an increase in binding with increased calcium, interactions between otoferlin C2F domain and intramolecular C2 domains occurred in the absence of calcium, consistent with intra-C2 domain interactions forming a “closed” tertiary structure at low calcium that “opens” as calcium increases. These results suggest a direct role for otoferlin in exocytosis and modulation of calcium-dependent membrane fusion. 相似文献
11.
Bennett R. Streit Ravi Kant Monika Tokmina-Lukaszewska Arianna I. Celis Melodie M. Machovina Eric P. Skaar Brian Bothner Jennifer L. DuBois 《The Journal of biological chemistry》2016,291(2):862-871
IsdGs are heme monooxygenases that break open the tetrapyrrole, releasing the iron, and thereby allowing bacteria expressing this protein to use heme as a nutritional iron source. Little is currently known about the mechanism by which IsdGs degrade heme, although the products differ from those generated by canonical heme oxygenases. A synthesis of time-resolved techniques, including in proteo mass spectrometry and conventional and stopped-flow UV/visible spectroscopy, was used in conjunction with analytical methods to define the reaction steps mediated by IsdG from Staphylococcus aureus and their time scales. An apparent meso-hydroxyheme (forming with k = 0.6 min−1, pH 7.4, 10 mm ascorbate, 10 μm IsdG-heme, 22 °C) was identified as a likely common intermediate with the canonical heme oxygenases. Unlike heme oxygenases, this intermediate does not form with added H2O2 nor does it convert to verdoheme and CO. Rather, the next observable intermediates (k = 0.16 min−1) were a set of formyloxobilin isomers, similar to the mycobilin products of the IsdG homolog from Mycobacterium tuberculosis (MhuD). These converted in separate fast and slow phases to β-/δ-staphylobilin isomers and formaldehyde (CH2O). Controlled release of this unusual C1 product may support IsdG''s dual role as both an oxygenase and a sensor of heme availability in S. aureus. 相似文献
12.
Anne M. Gardner Matthew R. Cook Paul R. Gardner 《The Journal of biological chemistry》2010,285(31):23850-23857
Cytoglobin (Cygb) was investigated for its capacity to function as a NO dioxygenase (NOD) in vitro and in hepatocytes. Ascorbate and cytochrome b5 were found to support a high NOD activity. Cygb-NOD activity shows respective Km values for ascorbate, cytochrome b5, NO, and O2 of 0.25 mm, 0.3 μm, 40 nm, and ∼20 μm and achieves a kcat of 0.5 s−1. Ascorbate and cytochrome b5 reduce the oxidized Cygb-NOD intermediate with apparent second order rate constants of 1000 m−1 s−1 and 3 × 106 m−1 s−1, respectively. In rat hepatocytes engineered to express human Cygb, Cygb-NOD activity shows a similar kcat of 1.2 s−1, a Km(NO) of 40 nm, and a kcat/Km(NO) (k′NOD) value of 3 × 107 m−1 s−1, demonstrating the efficiency of catalysis. NO inhibits the activity at [NO]/[O2] ratios >1:500 and limits catalytic turnover. The activity is competitively inhibited by CO, is slowly inactivated by cyanide, and is distinct from the microsomal NOD activity. Cygb-NOD provides protection to the NO-sensitive aconitase. The results define the NOD function of Cygb and demonstrate roles for ascorbate and cytochrome b5 as reductants. 相似文献
13.
Winifred O. Idigo Svetlana Reilly Mei Hua Zhang Yin Hua Zhang Raja Jayaram Ricardo Carnicer Mark J. Crabtree Jean-Luc Balligand Barbara Casadei 《The Journal of biological chemistry》2012,287(52):43665-43673
Myocardial constitutive No production depends on the activity of both endothelial and neuronal NOS (eNOS and nNOS, respectively). Stimulation of myocardial β3-adrenergic receptor (β3-AR) produces a negative inotropic effect that is dependent on eNOS. We evaluated whether nNOS also plays a role in β3-AR signaling and found that the β3-AR-mediated reduction in cell shortening and [Ca2+]i transient amplitude was abolished both in eNOS−/− and nNOS−/− left ventricular (LV) myocytes and in wild type LV myocytes after nNOS inhibition with S-methyl-l-thiocitrulline. LV superoxide (O2˙̄) production was increased in nNOS−/− mice and reduced by l-Nω-nitroarginine methyl ester (l-NAME), indicating uncoupling of eNOS activity. eNOS S-glutathionylation and Ser-1177 phosphorylation were significantly increased in nNOS−/− myocytes, whereas myocardial tetrahydrobiopterin, eNOS Thr-495 phosphorylation, and arginase activity did not differ between genotypes. Although inhibitors of xanthine oxidoreductase (XOR) or NOX2 NADPH oxidase caused a similar reduction in myocardial O2˙̄, only XOR inhibition reduced eNOS S-glutathionylation and Ser-1177 phosphorylation and restored both eNOS coupled activity and the negative inotropic and [Ca2+]i transient response to β3-AR stimulation in nNOS−/− mice. In summary, our data show that increased O2˙̄ production by XOR selectively uncouples eNOS activity and abolishes the negative inotropic effect of β3-AR stimulation in nNOS−/− myocytes. These findings provide unequivocal evidence of a functional interaction between the myocardial constitutive NOS isoforms and indicate that aspects of the myocardial phenotype of nNOS−/− mice result from disruption of eNOS signaling. 相似文献
14.
Streptomyces thermoautotrophicus sp. nov., a Thermophilic CO- and H2-Oxidizing Obligate Chemolithoautotroph 总被引:2,自引:0,他引:2
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Dilip Gadkari Karl Schricker Georg Acker Reiner M. Kroppenstedt Ortwin Meyer 《Applied microbiology》1990,56(12):3727-3734
The novel thermophilic CO- and H2-oxidizing bacterium UBT1 has been isolated from the covering soil of a burning charcoal pile. The isolate is gram positive and obligately chemolithoautotrophic and has been named Streptomyces thermoautotrophicus on the basis of G+C content (70.6 ± 0.19 mol%), a phospholipid pattern of type II, MK-9(H4) as the major quinone, and other chemotaxonomic and morphological properties. S. thermoautotrophicus could grow with CO (td = 8 h), H2 plus CO2 (td = 6 h), car exhaust, or gas produced by the incomplete combustion of wood. Complex media or heterotrophic substrates such as sugars, organic acids, amino acids, and alcohols did not support growth. Molybdenum was required for CO-autotrophic growth. For growth with H2, nickel was not necessary. The optimum growth temperature was 65°C; no growth was observed below 40°C. However, CO-grown cells were able to oxidize CO at temperatures of 10 to 70°C. Temperature profiles of burning charcoal piles revealed that, up to a depth of about 10 to 25 cm, the entire covering soil provides a suitable habitat for S. thermoautotrophicus. The Km was 88 μl of CO liter−1 and Vmax was 20.2 μl of CO h−1 mg of protein−1. The threshold value of S. thermoautotrophicus of 0.2 μl of CO liter−1 was similar to those of various soils. The specific CO-oxidizing activity in extracts with phenazinemethosulfate plus 2,6-dichlorophenolindophenol as electron acceptors was 246 μmol min−1 mg of protein−1. In exception to other carboxydotrophic bacteria, S. thermoautotrophicus CO dehydrogenase was able to reduce low potential electron acceptors such as methyl and benzyl viologens. 相似文献
15.
Chlorophyll a Fluorescence and Photosynthetic and Growth Responses of Pinus radiata to Phosphorus Deficiency, Drought Stress, and High CO(2) 总被引:2,自引:2,他引:0
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Needles from phosphorus deficient seedlings of Pinus radiata D. Don grown for 8 weeks at either 330 or 660 microliters CO2 per liter displayed chlorophyll a fluorescence induction kinetics characteristic of structural changes within the thylakoid chloroplast membrane, i.e. constant yield fluorescence (FO) was increased and induced fluorescence ([FP-FI]/FO) was reduced. The effect was greatest in the undroughted plants grown at 660 μl CO2 L−1. By week 22 at 330 μl CO2 L−1 acclimation to P deficiency had occurred as shown by the similarity in the fluorescence characteristics and maximum rates of photosynthesis of the needles from the two P treatments. However, acclimation did not occur in the plants grown at 660 μl CO2 L−1. The light saturated rate of photosynthesis of needles with adequate P was higher at 660 μl CO2 L−1 than at 330 μl CO2 L−1, whereas photosynthesis of P deficient plants showed no increase when grown at the higher CO2 concentration. The average growth increase due to CO2 enrichment was 14% in P deficient plants and 32% when P was adequate. In drought stressed plants grown at 330 μl CO2 L−1, there was a reduction in the maximal rate of quenching of fluorescence (RQ) after the major peak. Constant yield fluorescence was unaffected but induced fluorescence was lower. These results indicate that electron flow subsequent to photosystem II was affected by drought stress. At 660 μl CO2 L−1 this response was eliminated showing that CO2 enrichment improved the ability of the seedlings to acclimate to drought stress. The average growth increase with CO2 enrichment was 37% in drought stressed plants and 19% in unstressed plants. 相似文献
16.
17.
The scutella separated from germinating barley grains (Hordeum vulgare L. cv. Himalaya) took up the dipeptide [14C]glycylglycine (Gly-Gly) rapidly from incubation media. The pH optimum of the process was about 4.5, and the rate of uptake conformed to Michaelis-Menten kinetics with an apparent Km of 2.3 mm and Vmax of 41 μmole gram−1 hour−1. The uptake was strongly inhibited by dinitrophenol and cyanide and by lack of O2. 相似文献
18.
Control of logarithmic growth rates of tobacco callus tissue by cytokinins 总被引:2,自引:2,他引:0
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The growth rates of tobacco callus tissues on media containing 10−6 to 10 μm 6-(γ,γ-dimethylallylamino)purine (2iP) were measured. At concentrations of 10−4 μm and above growth rates were exponential and dependent on cytokinin concentration. At 2iP concentrations of 10−4 to 0.33 μm, the exponential rate was maintained for 4 to 5 doublings of fresh and dry weight. After this period a linear phase, resulting in approximately 1 doubling of weight, occurred. The growth of tissues on media containing higher than 0.33 μm 2iP was exponential for only about 15 days. At the end of this time, and well before they achieved half their final weight, they exhibited growth which was less rapid than logarithmic but more rapid than linear. Comparisons with zeatin, 6-benzylaminopurine and kinetin indicated that, although the maximum growth rates obtained with relatively high concentrations (0.1-1 μm) were similar, the naturally occurring cytokinins, 2iP and zeatin, promoted faster rates at lower concentrations (10−3-10−2 μm) than did 6-benzylaminopurine and kinetin. 相似文献
19.
Ahmet H. Badur Sujit Sadashiv Jagtap Geethika Yalamanchili Jung-Kul Lee Huimin Zhao Christopher V. Rao 《Applied and environmental microbiology》2015,81(5):1865-1873
Alginate lyases are enzymes that degrade alginate through β-elimination of the glycosidic bond into smaller oligomers. We investigated the alginate lyases from Vibrio splendidus 12B01, a marine bacterioplankton species that can grow on alginate as its sole carbon source. We identified, purified, and characterized four polysaccharide lyase family 7 alginates lyases, AlyA, AlyB, AlyD, and AlyE, from V. splendidus 12B01. The four lyases were found to have optimal activity between pH 7.5 and 8.5 and at 20 to 25°C, consistent with their use in a marine environment. AlyA, AlyB, AlyD, and AlyE were found to exhibit a turnover number (kcat) for alginate of 0.60 ± 0.02 s−1, 3.7 ± 0.3 s−1, 4.5 ± 0.5 s−1, and 7.1 ± 0.2 s−1, respectively. The Km values of AlyA, AlyB, AlyD, and AlyE toward alginate were 36 ± 7 μM, 22 ± 5 μM, 60 ± 2 μM, and 123 ± 6 μM, respectively. AlyA and AlyB were found principally to cleave the β-1,4 bonds between β-d-mannuronate and α-l-guluronate and subunits; AlyD and AlyE were found to principally cleave the α-1,4 bonds involving α-l-guluronate subunits. The four alginate lyases degrade alginate into longer chains of oligomers. 相似文献
20.
Successional Development of Sulfate-Reducing Bacterial Populations and Their Activities in a Wastewater Biofilm Growing under Microaerophilic Conditions 总被引:8,自引:4,他引:4
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Tsukasa Ito Satoshi Okabe Hisashi Satoh Yoshimasa Watanabe 《Applied microbiology》2002,68(3):1392-1402
A combination of fluorescence in situ hybridization, microprofiles, denaturing gradient gel electrophoresis of PCR-amplified 16S ribosomal DNA fragments, and 16S rRNA gene cloning analysis was applied to investigate successional development of sulfate-reducing bacteria (SRB) community structure and in situ sulfide production activity within a biofilm growing under microaerophilic conditions (dissolved oxygen concentration in the bulk liquid was in the range of 0 to 100 μM) and in the presence of nitrate. Microelectrode measurements showed that oxygen penetrated 200 μm from the surface during all stages of biofilm development. The first sulfide production of 0.32 μmol of H2S m−2 s−1 was detected below ca. 500 μm in the 3rd week and then gradually increased to 0.70 μmol H2S m−2 s−1 in the 8th week. The most active sulfide production zone moved upward to the oxic-anoxic interface and intensified with time. This result coincided with an increase in SRB populations in the surface layer of the biofilm. The numbers of the probe SRB385- and 660-hybridized SRB populations significantly increased to 7.9 × 109 cells cm−3 and 3.6 × 109 cells cm−3, respectively, in the surface 400 μm during an 8-week cultivation, while those populations were relatively unchanged in the deeper part of the biofilm, probably due to substrate transport limitation. Based on 16S rRNA gene cloning analysis data, clone sequences that related to Desulfomicrobium hypogeium (99% sequence similarity) and Desulfobulbus elongatus (95% sequence similarity) were most frequently found. Different molecular analyses confirmed that Desulfobulbus, Desulfovibrio, and Desulfomicrobium were found to be the numerically important members of SRB in this wastewater biofilm. 相似文献