首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
Biochemistry and physiology of aerobic carbon monoxide-utilizing bacteria   总被引:3,自引:0,他引:3  
Abstract The use of CO as a growth substrate by aerobic CO-oxidizing (carboxydotrophic) bacteria requires some features not obvious in other bacteria. These are the presence of the enzyme CO dehydrogenase, a branched respiratory chain with an alternative CO-insensitive terminal oxidase (cytochrome b 653) and formation of reduced pyridine nucleotides by a pmf-driven reversed electron transfer. Immunocytochemical localization studies revealed that CO dehydrogenase is attached to the inner aspect of the cytoplasmic membrane of Pseudomonas carboxydovorans . The enzyme is a molybdo iron-sulfur flavoprotein containing bactopterin as the organic portion of the molybdenum cofactor. Recent findings suggest that this novel pterin is universal to eubacterial molybdenum enzymes, whereas molybdopterin is universal to eukaryotic molybdoenzymes.  相似文献   

2.
Abstract The midpoint redox potentials (E'0) of the cytochromes of Pseudomonas carboxydovorans have been studied by means of coupled spectrum deconvolution and potentiometric analysis. Membranes of cells grown on different substrates (CO; H2+ CO2; or pyruvate) contained cytochromes with similar absorption peaks and redox potentials. The cytochromes of the CO-sensitive main electron pathway of the respiratory chain revealed redox potentials in the same range as mitochondrial cytochromes (cytochrome b -555, about −20 mV; cytochrome c and cytochrome a , about +220 mV). For the cytochromes of the CO-insensitive alternative electron pathway, which allows uninhibited growth and respiration in the presence of high concentrations of CO, redox potentials of approx. +50 mV (cytochrome b -558) and −11 to −215 mV (cytochrome b -561) were determined. Cytochrome [ib-561], earlier proposed as the alternative terminal oxidase o in this organism, was shown to possess the lowest half reduction potential of all the cytochromes present in the cells. Measurements of the apparent K m value for oxygen revealed a low affinity of cytochrome a ( K m/ 5 υ M O2) and a very high affinity of the CO-insensitive oxidase ( K m < 0.5 μ M O2). The high affinity to oxygen might be responsible for the CO-insensitivity of this unusual cytochrome o .  相似文献   

3.
Cell extracts from acetate-grown Methanosarcina thermophila contained CO-oxidizing:H2-evolving activity 16-fold greater than extracts from methanol-grown cells. Following fractionation of cell extracts into soluble and membrane components, CO-dependent H2 evolution and CO-dependent methyl-coenzyme M methylreductase activities were only present in the soluble fraction, but addition of the membrane fraction enhanced both activities. A b-type cytochrome(s), present in the membrane fraction, was linked to a membrane-bound hydrogenase. CO-oxidizing:H2-evolving activity was reconstituted with: (i) CO dehydrogenase complex, (ii) a ferredoxin, and (iii) purified membranes with associated hydrogenase. The ferredoxin was a direct electron acceptor for the CO dehydrogenase complex. The ferredoxin also coupled CO oxidation by CO dehydrogenase complex to metronidazole reduction.  相似文献   

4.
The role of O2 photoreduction was studied in intact cells of normal and photobleached Anabaena cylindrica Lemm. strain PCC 7122. We found that O2 photoreduction represents a protective mechanism against over-reduction of the photosyn-thetic electron transport chain only in normal Anabaena cells. This protective mechanism was not functioning in photobleached cells in spite of the increased rate of photosynthetic electron flow. A new electron acceptor, the induced reversible hydrogenase, is suggested to be operating in photobleached Anabaena cylindrica .  相似文献   

5.
Abstract Soluble fractions prepared from cells of Pseudomonas carboxydovorans bearing a small plasmid (1.76 × 106) exhibited proteolytic activity on the β-subunit of CO dehydrogenase (CO-DH) in plasmid-cured cells of the same strain, implying that the plasmid carries gene(s) for processing the β subunit of the enzyme at the post-translational level. The protease was found to be a constitutive enzyme. It did not hydrolyze the β subunit of CO-DH in Pseudomonas carboxydohydrogena . Analysis of CO-DH after transformation of the cured cells with the small plasmid confirmed that the plasmid plays a role in the modification of the β subunit of CO-DH in P. carboxydovorans .  相似文献   

6.
Abstract The thermostability of the ATP phosphohydrolase of the facultative thermophile Bacillus coagulans has been investigated. Fractionation of disintegrated cell suspensions by differential centrifugation revealed a similar distribution of enzyme activity irrespective of growth temperature. Most of the activity was located in the membrane fraction. Thermostability of solubilized (BF1) preparation from cells grown at 37°C or 55°C was similar, but membrane-bound BF0BF1 from 37°C-grown cells was inactivated at lower temperatures than that from 55°C-grown cells.
Inhibition of the membrane-bound (BF0BF1)ATPase by 4-chloro-7-nitro-benzofuran (NbfCl) and quercetin, which both act on the BF1 portion of the enzyme, was different from that seen with the soluble (BF1) enzyme. The results show that some modification of BF1 must occur when the enzyme is membrane-bound.  相似文献   

7.
The expression and activity of type 1 NAD(P)H dehydrogenase (NDH-1) were investigated in Synechocystis PCC 6803 cells during different growth phases (i.e. lag, logarithmic, stationary and decline phases). The relative amount of NDH-1, estimated by Western blot analysis using antibodies against NdhH, NdhI and NdhK, increased more than two-fold during growth from the lag to the logarithmic phase and then decreased after the logarithmic phase to reach lowest levels after 15 days (decline phase). The activity of light-dependent NADPH oxidation and cyclic electron flow around photosystem I (PSI) changed nearly in parallel with the amount of NdhH, NdhI and NdhK in cells across the growth phases. In contrast, the activity of photosynthetic O2 evolution and respiratory O2 uptake was not significantly different across phases of growth; the fluctuation of the activity at different phases was within 40%. These results suggested that the activity of light-dependent NADPH oxidation and PSI-cyclic electron flow are restricted by the amount of NDH-1 and that other factor(s) are limiting the rates of photosynthesis and respiration.  相似文献   

8.
Extracts of aerobically, CO-autotrophically grown cells of Pseudomonas carboxydovorans were shown to catalyze the oxidation of CO to CO(2) in the presence of methylene blue, pyocyanine, thionine, phenazine methosulfate, or toluylene blue under strictly anaerobic conditions. Viologen dyes and NAD(P)(+) were ineffective as electron acceptors. The same extracts catalyzed the oxidation of formate and of hydrogen gas; the spectrum of electron acceptors was identical for the three substrates, CO, formate, and H(2). The CO- and the formate-oxidizing activities were found to be soluble enzymes, whereas hydrogenase was membrane bound exclusively. The rates of oxidation of CO, formate, and H(2) were measured spectrophotometrically following the reduction of methylene blue. The rate of carbon monoxide oxidation followed simple Michaelis-Menten kinetics; the apparent K(m) for CO was 45 muM. The reaction rate was maximal at pH 7.0, and the temperature dependence followed the Arrhenius equation with an activation energy (DeltaH(0)) of 35.9 kJ/mol (8.6 kcal/mol). Neither free formate nor hydrogen gas is an intermediate of the CO oxidation reaction. This conclusion is based on the differential sensitivity of the activities of formate dehydrogenase, hydrogenase, and CO dehydrogenase to heat, hypophosphite, chlorate, cyanide, azide, and fluoride as well as on the failure to trap free formate or hydrogen gas in coupled optical assays. These results support the following equation for CO oxidation in P. carboxydovorans: CO + H(2)O --> CO(2) + 2 H(+) + 2e(-) The CO-oxidizing activity of P. carboxydovorans differed from that of Clostridium pasteurianum by not reducing viologen dyes and by a pH optimum curve that did not show an inflection point.  相似文献   

9.
The effect of Zn2+ on the plasma membrane permeability and superoxide radical (O2-) formation in roots was studied with cotton ( Gossypium hirsutum L. cv. Delta-pine 15/21) plants grown in nutrient solution with different Zn2+ supply. Compared to Zn-sufficient plants, the plasma membrane permeability of Zn-deficient plants was increased as indicated by a 3-, 5- and 2.5-fold increase in root cell leakage of K+, NO3- and organic carbon compounds, respectively. Resupply of Zn2+ to Zn-deficient plants for 12 h substantially decreased this leakage. The effects of Zn2+ on membrane permeability were closely correlated with the levels of O2- measured by electron spin resonance (ESR) spectroscopy in the microsomal membrane fraction and in the cytosol fraction of root cells. The amplitudes of the O2- -derived Tiron ESR signal also coincided with a O2- -generating oxidase activity which was strongly dependent on the presence of NADPH and FAD. The results suggest that Zn2+ directly affects the integrity of the plasma membrane, at least in part, by interfering with O2- generation by a membrane-bound NADPH oxidase.  相似文献   

10.
In Pseudomonas carboxydovorans, CO dehydrogenase and hydrogenase were found in association with the cytoplasmic membrane in a weakly bound and a tightly bound pool. The pools could be experimentally distinguished on the basis of resistance to removal by washes in low-ionic-strength buffer. The tightly bound pool of the enzymes could be differentially solubilized under conditions leaving the electron transport system intact and with the nondenaturing zwitterionic detergent 3-(3-cholamidopropyl) dimethylammonio 1-propane-sulfonic acid (CHAPS) and the nonionic detergent dodecyl beta-D-maltoside. In vitro reconstitution of depleted membranes with the corresponding supernatants containing CO dehydrogenase led to binding of the enzyme and to reactivation of respiratory activities with CO. The reconstitution reaction required cations with effectiveness which increased with increasing ionic charge: monovalent (Li+), divalent (Mg2+, Mn2+), or trivalent (Cr3+, La3+). Reconstitution of depleted membranes with CO dehydrogenase was specific for CO-grown bacteria. Cytoplasmic membranes from H2- or heterotrophically grown Pseudomonas carboxydovorans had no affinity for CO dehydrogenase at all, indicating the absence of the physiological electron acceptor of the enzyme, which presumably is cytochrome b561, or another membrane anchor.  相似文献   

11.
Abstract. Modifications in plasma membrane structure and permeability were observed in Chlorella sorokiniana following exposure to 0.2 gm−3(140 p.p.m.) O3 for 30 min. Sixty-eight per cent of the cells were plasmolysed after 15 min O3 exposure with disruption of organelles similar to that previously described in higher plants. Freeze-fracture exposed large areas of plasma membrane in 90% of the control cells and those exposed to O3for short periods. After 20 min O3 90% of the cells cross-fracture, which indicates a change in molecular interactions in the membrane exposed to O3 The earliest observed ultraslructural alteration is an aggregation of particles on the plasma membrane P face, statistically significant after 10 min O3 Changes in 86Rb influx occur during a similar time. After more extended exposure to O3 the plasma membrane P face shows regions of lipid phase transition to the crystalline state.  相似文献   

12.
Plasma membrane ferric reductase activity was enhanced 5-fold under iron limitation in the unicellular green alga Chlorella kessleri Fott et Nováková. Furthermore, ferric reductase activity in iron-limited cells was approximately 50% higher in the light than in the dark. In contrast, iron uptake rates of iron-limited cells were unaffected by light versus dark treatments. Rates of iron uptake were much lower than rates of ferric reduction, averaging approximately 2% of the dark ferric reduction rate. Ferric reduction was associated with an increased rate of O2 consumption in both light and dark, the increase in the light being approximately 1.5 times as large as in the dark. The increased rate of O2 consumption could be decreased by half by the addition of catalase, indicating that H2O2 is the product of the O2 consumption and that the increased O2 consumption is nonrespiratory. The stimulation of O2 consumption was almost completely abolished by the addition of bathophenanthroline disulfonate, a strong chelator of Fe2 + . Anaerobic conditions or the presence of exogenous superoxide dismutase affected neither ferric reduction nor iron uptake. We suggest that the O2 consumption associated with ferric reductase activity resulted from superoxide formation from the aerobic oxidation of Fe2 + , which is the product of ferric reductase activity. At saturating concentrations of Fe3 + chelates, ferric reductase activity is much greater than the iron uptake rate, leading to rapid oxidation of Fe2 + and superoxide generation. Therefore, O2 consumption is not an integral part of the iron assimilation process.  相似文献   

13.
Submitochondrial particles (SMP) were isolated from potato ( Solanum tuberosum L. cv. Bintje) tubers. The SMP were 91% inside-out and they were able to form a membrane potential, as monitored by oxonol VI, with succinate, NADH and NADPH. The pH dependence and kinetics of NADH and NADPH oxidation by these SMP was studied using three different electron acceptors – O2, duroquinone and ferricyanide. In addition, the SMP were solubilized, fractionated by non-denaturing polyacrylamide gel electrophoresis, and the gels were stained for NAD(P)H dehydrogenase activity and specificity at different pH using Nitro Blue Tetrazolium. From the results we conclude that there are at least two distinct NAD(P)H dehydrogenases on the inner surface of the inner membrane: (1) Complex 1 which oxidizes NADH and deamino-NADH in a rotenone-sensitive manner, (O2 as acceptor) with optimum activity at pH 8 and a very low Km(NADH) of 3 μ M . It also oxidizes NADPH and deamino-NADPH in a rotenone-sensitive manner, but with a pH optimum at pH 5.8 and a very high Km(NADPH) of more than 1 m M . This complex is found as a broad, diffuse band at the top of the gels. (2) A second dehydrogenase which oxidizes NADH in a rotenone-insensitive manner with optimum activity at pH 6.2 and a higher Km(NADH) of 14 μ M . It also oxidizes NADPH in a rotenone-insensitive manner with an activity optimum at pH 6.8 and low Km(NADPH) of 25 μ M . This dehydrogenase does not oxidize deamino-NAD(P)H. One of the sharp bands around the middle of the native gels may be caused by this dehydrogenase indicating that it has a relatively low molecular mass compared to Complex I. Several other NAD(P)H dehydrogenase bands were observed on the gels which we cannot yet assign.  相似文献   

14.
Oxygen and the regulation of nitrogen fixation in legume nodules   总被引:3,自引:0,他引:3  
In N2-fixing legume nodules, O2 is required in large amounts for aerobic respiration, yet nitrogenase, the bacterial enzyme that fixes N2, is O2 labile. A high rate of O2 consumptition and a cortical barrier to gas diffusion work together to maintain a low, non-inhibitory O2 concentration in the central, infected zone of the nodule. At this low O2 concentration, cytosolic leghemoglobin is required to facilitate the diffusion of O2 through the infected cell to the bacteria. The resistance of the cortical diffusion barrier is variable and is used by legume nodules to regulate the O2 concentration in the infected cells such that it limits aerobic respiration and N2 fixation at all times. The resistance of the diffusion barrier and therefore the degree of O2 limitation seems to be regulated in response to changes in the O2 concentration of the central infected zone, the supply of phloem sap to the nodule, and the rate of N assimilation into the end products of fixation.  相似文献   

15.
Abstract A diatom biofilm was grown in a chamber developed for culture of biofilms in chemical gradients. The diatoms grew on a polycarbonate membrane filter which separated a sterile reservoir, with added phosphate, from a reservoir without phosphate. Within 3 weeks of inoculation, a thick biofilm developed on the surface of the filter. The biofilms were homogeneous and therefore suitable for calculations of O2 diffusion fluxes from concentration profiles of O2. Profiles of O2, pH, and gross photosynthesis at different light intensities and liquid medium concentrations of dissolved inorganic carbon and O2 were measured with microelectrodes. Respiratory activity in a layer of the biofilm was determined as the difference between gross photosynthesis and outflux of O2 from that layer. The photosynthetic activity in a well-developed biofilm grown at 360 μEinst m−2 s−1 and 2.4 mM HCO3 was limited by the supply of inorganic carbon. Exposure to light above 360 μEinst m−2 s−1 stimulated gross photosynthesis as well as respiratory processes without affecting net outflux of O2. Higher concentrations of inorganic carbon, on the other hand, enhanced gross photosynthesis without concurrent increase in respiratory rate, resulting in an increased outflux of O2. High concentrations of O2 in the liquid medium decreased the net outflux of O2 with little effect on the gross photosynthesis. The effects of inorganic carbon and O2 on the metabolic activities of the biofilm were consistent with the presence of photorespiratory activity.  相似文献   

16.
Differences in mitochondrial membrane composition and ultrastructure were studied after storage of cauliflower ( Brassica oleracea , L., Botrytis group) for 5 days at 25°C in air or under controlled atmospheres: 3% O2, 21% O2+ 15% CO2 or 3% O2+ 15% CO2. In air, postharvest senescence involved a 20% decrease in mitochondrial phospholipid content. A large reduction in the relative abundance of phosphati-dylcholine (PC) and in the degree of unsaturation of PC and phosphatidyl ethanolamine (PE) was observed. However, the degree of unsaturation increased in cardiolipin (CL). Storage under 3% O2 did not prevent phospholipid breakdown. Low O2 prevented the relative decrease in PC observed during storage in air and the loss of linoleic acid from PC, but not from PE. This relative protection offered by the low O2 atmosphere was lost under 3% O2+ 15% CO2. The high CO2 atmospheres caused twice as much loss in phospholipids as that observed during storage in air. Extensive loss of mitochondrial protein, a marked decrease in phospholipid to protein ratio, and electron micrograph observations suggest structural alterations in the presence of high CO2.  相似文献   

17.
Abstract The extent of recovery of nitrogenase activity of Gloeothece transferred from an atmosphere of O2 to air depended on the duration of exposure to O2. Activity recovered at increasing rates after up to 24 h exposure to O2 and a lag before detection of activity, present after short (1 h) exposure times, disappeared with longer exposures. Synthesis of nitrogenase de novo was implicated, since chloramphenicol, tetracycline, or repressive levels of NH+4, prevented recovery of activity. Specific radioimmunoassay of the rate of synthesis of the MoFe protein of nitrogenase under O2 correlated well with the activity measurements, and indicate that a shift from air to O2 only transiently represses nitrogenase synthesis.  相似文献   

18.
Abstract Isolation of plasmid DNA followed by plasmid curing was carried out to examine the relationship of plasmid to carbon monoxide dehydrogenase (CO-DH) production in carboxydobacteria. A small plasmid of almost identical size (1.52−1.76 × 106) was present in Pseudomonas carboxydovorans, Azotobacter sp.1, and Azomonas sp.2. Azomonas sp.1 contained two kinds of plasmids (1.5 × 106 and 2.47 × 106). No plasmids were found in Pseudomonas carboxydohydrogena , JC1, and HY1. A plasmid-cured clone of P. carboxydovorans was obtained by growing the cells at 37°C. The cured cell was able to grow CO autotrophically on solid, but not in liquid, medium. CO-DH of the cured cell was active and consisted of three subunits similar to those found in the wild-type enzyme, with the exception that the β subunit of the enzyme was larger than that of the wild-type enzyme. These results suggest that the small plasmids do not carry genes encoding CO-DH but may have gene(s) for processing the β subunit of the enzyme.  相似文献   

19.
The deeply purple cyanobacterium Gloeobacter violaceus is subject of this investigation. It does not contain thylakoids, and the photosynthetic apparatus is located in the only membrane of the cell, the plasma membrane. Upon excitation with blue light, the 77 K fluorescence emission spectra of neither intact cells (excited with 427 nm) nor of the isolated plasma membrane (excited with 430 nm), show the expected long wavelength photosystem I emission characteristic for low energy chlorophylls. Maximal fluorescence emission was observed at 688 nm. independent on the excitation wavelength, 427 (430) nm blue light, exciting mainly chlorophyll, or 550 nm green light, exciting mainly phycoerythin. The ratio of P700 to chlorophyll was 175. O2-evolution was 160 μmol mg-1 chlorophyll h-1 in saturating white light; the compensation point was reached at 6 μmol m2 s-1 in cultures grown at 25 μmol m2 s-1. Dark O2 uptake was 50 μmol mg-1 chlorophyll h-1. During adaptation to increasing white light intensities Gloeobacter reduces the amount of phycocyanin and chlorophyll per cell and strongly increases the concentration of carotenoids relative to chlorophyll. The carotenoid concentration per cell increases with increasing light intensity. Apparently, part of the carotenoids is not located in the plasma membrane.  相似文献   

20.
In Chlorella vulgaris UAM 101, the presence of glucose altered the photosynthetic and respiratory metabolism in the light. When glucose was added to the growth medium, an increase in the cellular level of enzymes involved in glucose oxidation, namely glucose-6-P dehydrogenase (EC 1.1.1.49) and NAD+-glyceraldehyde-3-P dehydrogenase (EC 1.2.1.12), was observed. Glucose also enhanced respiratory O2 consumption. In addition, CO2 released by glucose oxidation was refixed in photosynthesis. The presence of glucose also affected photosynthesis. Phosphoribulokinase (EC 2.7.1.19) and NADP+-dependent glyceraldehyde-3-P dehydrogenase (EC 1.2.1.13), two regulatory enzymes of the reductive pentose phosphate cycle, were increased by glucose. However, Rubisco (EC 4.1.1.39) activity of these cells was lower than that of autotrophic cells. Despite these alterations, the photosynthetic O2 evolution was not significantly inhibited by glucose. On the other hand, an increase in the cytosolic NADP+-glyceraldehyde-3-P dehydrogenase (EC 1.2.1.9) that is involved in obtaining reducing power for anabolic processes was observed. The CO2 levels in the growth medium did not significantly affect the cellular level of enzymes measured in this work, except those involved in biosynthetic pathways. These data suggest that the effect of glucose on photosynthesis and respiration can be explained by alteration of the cellular level of photosynthetic enzymes and respiratory substrates, respectively.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号