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1.
Purification of a hexaheme cytochrome c552 from Escherichia coli K 12 and its properties as a nitrite reductase 总被引:2,自引:0,他引:2
Anaerobic cytochrome c552 was purified to electrophoretic homogeneity by ion-exchange chromatography and gel filtration from a mutant of Escherichia coli K 12 that synthesizes an increased amount of this pigment. Several molecular and enzymatic properties of the cytochrome were investigated. Its relative molecular mass was determined to be 69 000 by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. It was found to be an acidic protein that existed in the monomeric form in the native state. From its heme and iron contents, it was concluded to be a hexaheme protein containing six moles of heme c/mole protein. The amino-acid composition and other properties of the purified cytochrome c552 indicated its similarity to Desulfovibrio desulfuricans hexaheme cytochrome. The cytochrome c552 showed nitrite and hydroxylamine reductase activities with benzyl viologen as an artificial electron donor. It catalyzed the reduction of nitrite to ammonia in a six-electron transfer. FMN and FAD also served as electron donors for the nitrite reduction. The apparent Michaelis constants for nitrite and hydroxylamine were 110 microM and 18 mM, respectively. The nitrite reductase activity of the cytochrome c552 was inhibited effectively by cupric ion and cyanide. 相似文献
2.
C4 photosynthesis in a single C3 cell is theoretically inefficient but may ameliorate internal CO2 diffusion limitations of C3 leaves 总被引:1,自引:1,他引:1
S. VON CAEMMERER 《Plant, cell & environment》2003,26(8):1191-1197
Attempts are being made to introduce C4 photosynthetic characteristics into C3 crop plants by genetic manipulation. This research has focused on engineering single‐celled C4‐type CO2 concentrating mechanisms into C3 plants such as rice. Herein the pros and cons of such approaches are discussed with a focus on CO2 diffusion, utilizing a mathematical model of single‐cell C4 photosynthesis. It is shown that a high bundle sheath resistance to CO2 diffusion is an essential feature of energy‐efficient C4 photosynthesis. The large chloroplast surface area appressed to the intercellular airspace in C3 leaves generates low internal resistance to CO2 diffusion, thereby limiting the energy efficiency of a single‐cell C4 concentrating mechanism, which relies on concentrating CO2 within chloroplasts of C3 leaves. Nevertheless the model demonstrates that the drop in CO2 partial pressure, pCO2, that exists between intercellular airspace and chloroplasts in C3 leaves at high photosynthetic rates, can be reversed under high irradiance when energy is not limiting. The model shows that this is particularly effective at lower intercellular pCO2. Such a system may therefore be of benefit in water‐limited conditions when stomata are closed and low intercellular pCO2 increases photorespiration. 相似文献
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Ichiro Yamato Hiro Nakamura Hiroshi Murakami Yasuhiro Anraku 《FEMS microbiology letters》1988,56(1):21-27
Abstract The cybB gene on a plasmid encoding cytochrome b 561 in Escherichia coli was disrupted by insertion of Kmrl determinant DNA. The cromosomal cybB gene was replaced by the inactivated cybB gene on the plasmid by homologous recombination using λ phage lysogenization and heat-induction. The replacement was confirmed by Southern and Western blotting analyses. Deficiency on the cybB gene product did not affect the growth properties of the cells, and the oxidase activities of the cells dependent on various substrates were similar to those of the parental strain. Cytochrome b 561 is concluded to be expressed in E. coli , but may not play a major role in cell growth. In the genetic map of E. coli , the cybB gene was determined by conjugational and transductional crosses to be at 31 min between trg and terC . 相似文献
5.
Lewis H. Ziska 《Global Change Biology》2000,6(8):899-905
Soybean (Glycine max) was grown at ambient and enhanced carbon dioxide (CO2, + 250 μL L?1 above ambient) with and without the presence of a C3 weed (lambsquarters, Chenopodium album L.) and a C4 weed (redroot pigweed, Amaranthus retroflexus L.), in order to evaluate the impact of rising atmospheric carbon dioxide concentration [CO2] on crop production losses due to weeds. Weeds of a given species were sown at a density of two per metre of row. A significant reduction in soybean seed yield was observed with either weed species relative to the weed‐free control at either [CO2]. However, for lambsquarters the reduction in soybean seed yield relative to the weed‐free condition increased from 28 to 39% as CO2 increased, with a 65% increase in the average dry weight of lambsquarters at enhanced [CO2]. Conversely, for pigweed, soybean seed yield losses diminished with increasing [CO2] from 45 to 30%, with no change in the average dry weight of pigweed. In a weed‐free environment, elevated [CO2] resulted in a significant increase in vegetative dry weight and seed yield at maturity for soybean (33 and 24%, respectively) compared to the ambient CO2 condition. Interestingly, the presence of either weed negated the ability of soybean to respond either vegetatively or reproductively to enhanced [CO2]. Results from this experiment suggest: (i) that rising [CO2] could alter current yield losses associated with competition from weeds; and (ii) that weed control will be crucial in realizing any potential increase in economic yield of agronomic crops such as soybean as atmospheric [CO2] increases. 相似文献
6.
Bamford VA Angove HC Seward HE Thomson AJ Cole JA Butt JN Hemmings AM Richardson DJ 《Biochemistry》2002,41(9):2921-2931
The crystal structure and spectroscopic properties of the periplasmic penta-heme cytochrome c nitrite reductase (NrfA) of Escherichia coli are presented. The structure is the first for a member of the NrfA subgroup that utilize a soluble penta-heme cytochrome, NrfB, as a redox partner. Comparison to the structures of Wolinella succinogenes NrfA and Sulfospirillum deleyianum NrfA, which accept electrons from a membrane-anchored tetra-heme cytochrome (NrfH), reveals notable differences in the protein surface around heme 2, which may be the docking site for the redox partner. The structure shows that four of the NrfA hemes (hemes 2-5) have bis-histidine axial heme-Fe ligation. The catalytic heme-Fe (heme 1) has a lysine distal ligand and an oxygen atom proximal ligand. Analysis of NrfA in solution by magnetic circular dichroism (MCD) suggested that the oxygen ligand arose from water. Electron paramagnetic resonance (EPR) spectra were collected from electrochemically poised NrfA samples. Broad perpendicular mode signals at g similar 10.8 and 3.5, characteristic of weakly spin-coupled S = 5/2, S = 1/2 paramagnets, titrated with E(m) = -107 mV. A possible origin for these are the active site Lys-OH(2) coordinated heme (heme 1) and a nearby bis-His coordinated heme (heme 3). A rhombic heme Fe(III) EPR signal at g(z) = 2.91, g(y) = 2.3, g(x) = 1.5 titrated with E(m) = -37 mV and is likely to arise from bis-His coordinated heme (heme 2) in which the interplanar angle of the imidazole rings is 21.2. The final two bis-His coordinated hemes (hemes 4 and 5) have imidazole interplanar angles of 64.4 and 71.8. Either, or both, of these hemes could give rise to a "Large g max" EPR signal at g(z)() = 3.17 that titrated at potentials between -250 and -400 mV. Previous spectroscopic studies on NrfA from a number of bacterial species are considered in the light of the structure-based spectro-potentiometric analysis presented for the E. coli NrfA. 相似文献
7.
The cytochrome c2 structural gene, cycA, from Rhodobacter sphaeroides was expressed in Escherichia coli. CycA-specific mRNA was detected in E. coli both under aerobic and anaerobic conditions with trimethylamine-N-oxide as electron acceptor. However mature holocytochrome c2 was only detected in anaerobically-grown cells. The mature form of cytochrome c2 (Mr = 12,500) was secreted into the periplasm of E. coli suggesting that the signal polypeptide was processed. The cytochrome c2 synthesized in E. coli exhibited absorbance maxima in the reduced form at 550 nm (alpha-band) and 521 nm (beta-band) and contained covalently attached haem c. The results indicate that a foreign c-type cytochrome can be secreted and assembled in E. coli under anaerobic conditions. 相似文献
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The specific activity of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco, EC 4.1.1.39) was measured from the crude extracts of five C3 plants consisting of wheat ( Triticum aestivum L. cv. Maris Mink), spinach ( Spinacia oleracea L.), pea ( Pisum sativum L. cv. Greenfeast), pumpkin ( Cucurbita pepo L. cv. Jättiläismeloni) and Ceratodon purpureus (Hedw.) Brid., and two C4 plants, maize ( Zea mays L. ETA F1 ) and sugar sorghum [ Sorghum saccharatum (L. emend, L.) Moench]. The amount of Rubisco in the crude extracts was estimated by polyacrylamide gel electro-phoresis with the Coomassie Brilliant Blue staining procedure. The amounts of the dye bound to the purified Rubisco of different higher plants were similar. The method gave a linear response for both purified enzyme and crude extracts, and the results agreed with those observed by immunochemical methods. The addition of positive effectors such as inorganic phosphate was necessary to obtain maximal activity in the crude extracts of all the studied plants except in that of maize. No significant differences in the specific carboxylase activity at 25°C were found between the C3 and C4 plants. 相似文献
10.
Abstract Gas chromatographic analyses revealed that rates of release of nitrous oxide from nitrite or nitric oxide in extracts of the c , d 1 cytochrome nitrite reductase-producing denitrifiers, Paracoccus denitrificans and Pseudomonas perfectomarina , were unaffected by preincubation with the metal chelator, diethyldithiocarbamate (DDC). In contrast, preincubation with DDC completely inhibited generation of nitrous oxide from nitrite in extracts of copper protein nitrite reductase-producing denitrifiers, " Achromobacter cycloclastes " and Rhodopseudomonas sphaeroides forma species denitrificans . Pre-exposure to DDC lessened but did not completely inhibit nitric oxide reduction in extracts of the copper protein nitrite reductase-producing denitrifiers. Proton consumption values resulting from pulsing with nitrite were similarly completely inhibited by preincubation with DDC of extracts of the two copper protein-producing denitrifiers. Uptake values related to pulsing with nitric oxide were also lessened but not completely inhibited by prior exposure to DDC. As anticipated, proton consumption was not affected by preincubation with DDC in extracts of P. denitrificans pulsed with nitrite or nitric oxide. Differential sensitivity of copper protein nitrite reductase activity to DDC could provide the simple assay method needed for determination of the distribution of two types of nitrite reductase producers among populations of denitrifiers in nature. 相似文献
11.
The effects of elevated atmospheric CO2 concentration on plant-fungi and plant-insect interactions were studied in an emergent marsh in the Chesapeake Bay. Stands of the C3 sedge Scirpus olneyi Grey, and the C4 grass Spartina patens (Ait.) Muhl. have been exposed to elevated atmospheric CO2 concentrations during each growing season since 1987. In August 1991 the severities of fungal infections and insect infestations were quantified. Shoot nitrogen concentration ([N]) and water content (WC) were determined. In elevated concentrations of atmospheric CO2, 32% fewer S. olneyi plants were infested by insects, and there was a 37% reduction in the severity of a pathogenic fungal infection, compared with plants grown in ambient CO2 concentrations. S. olneyi also had reduced [N], which correlated positively with the severities of fungal infections and insect infestations. Conversely, S. patens had increased WC but unchanged [N] in elevated concentrations of atmospheric CO2 and the severity of fungal infection increased. Elevated atmospheric CO2 concentration increased or decreased the severity of fungal infection depending on at least two interacting factors, [N] and WC; but it did not change the number of plants that were infected with fungi. In contrast, the major results for insects were that the number of plants infected with insects decreased, and that the amount of tissue that each insect ate also decreased. 相似文献
12.
The gene coding for Pseudomonas aeruginosa cytochrome c551 has been cloned and its nucleotide sequence determined. Cytochrome c551 is expressed as a 104 amino acid pre-protein from which a signal peptide of 22 amino acids is cleaved off during the translocation across the cytoplasmic membrane. The gene is located just downstream of the gene coding for nitrite reductase on the Pseudomonas aeruginosa chromosome, suggesting that these genes form an operon. 相似文献
13.
Achievable productivities of certain CAM plants: basis for high values compared with C3 and C4 plants 总被引:2,自引:1,他引:2
PARK S. NOBEL 《The New phytologist》1991,119(2):183-205
14.
Variable factors affecting the enzymatic isolation of mesophyll protoplasts from Triticum aestivum (wheat), a C3 gras, and mesophyll protoplasts and bundle sheath strands from Digitaria sanguinalis (crabgrass), a C4 grass, have been examined with respect to yields and also photosynthetic capacity after isolation. Preparations with high yields and high photosynthetic capacity were obtained when small transverse leaf segments were incubated in enzyme medium in the light at 30°C, without mechanical shaking and without prior vacuum infiltration. Best results were obtained with an enzyme medium that included 0.5 M sorbitol, 1 mM MgCl2, 1 mM KH2PO4, 2% cellulase and 0.1% pectinase at pH 5.5. In gerneral, leaf age and leaf segment size were important factors, with highest yields and photosynthetic capacities obtained from young leaves cut into segments less than 0.8 mm. To facilitate the cutting of such small segments, a mechanical leaf cutter is described that uniformly (± 0.05 mm) cuts leaf tissue into transverse segments of variable size (0.4–2 mm). Isolations that required more than roughly 4 h gave poor yields with reduced photosynthetic capacity; however, using the optimum conditions described, functional preparations could be roughly 2 h. High rates of light dependent CO2 fixation by the C4 mesophyll protoplasts required the addition of pyruvate and low levels of oxalacetate, while isolated bundle sheath strands and C3 mesophyll protoplasts supported CO2 fixation without added substrates. Rates of CO2 fixation by isolated wheat protoplasts generally exceeded the reported rates of whole leaf photosynthesis. Wheat mesophyll protoplasts and crabgrass bundle sheath strands were stable when stored at 4°C while C4 mesophyll protoplasts were stable when stored at 25°C. 相似文献
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Silvia Rossbach Hannes Loferer Gonzalo Acuña Cyril A. Appleby Hauke Hennecke 《FEMS microbiology letters》1991,83(2):145-152
We report the cloning and nucleotide sequence analysis of the cytochrome c552 gene (cycB) of Bradyrhizobium japonicum strain 110. The gene was identified with help of an oligonucleotide that was designed on the basis of the amino acid sequence determined for purified cytochrome c552 of B. japonicum strain CC705. The cycB gene product has an N-terminal 23-amino acid signal peptide that is missing in the mature cytochrome c552 protein. A B. japonicum cycB insertion mutant was constructed which had no observable phenotypic defects in denitrification and symbiotic nitrogen fixation. Thus, the function of c552 remains unknown. 相似文献
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In this study, the response of N2 fixation to elevated CO2 was measured in Scirpus olneyi, a C3 sedge, and Spartina patens, a C4 grass, using acetylene reduction assay and 15N2 gas feeding. Field plants grown in PVC tubes (25 cm long, 10 cm internal diameter) were used. Exposure to elevated CO2 significantly (P < 0·05) caused a 35% increase in nitrogenase activity and 73% increase in 15N incorporated by Scirpus olneyi. In Spartina patens, elevated CO2 (660 ± 1 μ mol mol − 1) increased nitrogenase activity and 15N incorporation by 13 and 23%, respectively. Estimates showed that the rate of N2 fixation in Scirpus olneyi under elevated CO2 was 611 ± 75 ng 15N fixed plant − 1 h − 1 compared with 367 ± 46 ng 15N fixed plant − 1 h − 1 in ambient CO2 plants. In Spartina patens, however, the rate of N2 fixation was 12·5 ± 1·1 versus 9·8 ± 1·3 ng 15N fixed plant − 1 h − 1 for elevated and ambient CO2, respectively. Heterotrophic non-symbiotic N2 fixation in plant-free marsh sediment also increased significantly (P < 0·05) with elevated CO2. The proportional increase in 15N2 fixation correlated with the relative stimulation of photosynthesis, in that N2 fixation was high in the C3 plant in which photosynthesis was also high, and lower in the C4 plant in which photosynthesis was relatively less stimulated by growth in elevated CO2. These results are consistent with the hypothesis that carbon fixation in C3 species, stimulated by rising CO2, is likely to provide additional carbon to endophytic and below-ground microbial processes. 相似文献
19.
Renate Scheibe 《Physiologia plantarum》1987,71(3):393-400
The thioredoxin-dependent light/dark modulation system of the chloroplast is described as a prerequisite enabling the flexible control of fluxes through the various parts of the CO2 -fixation pathway. Both the rapid turnover of the reduced thiol-containing form of the respective target enzyme, and the metabolite effect upon the reductive enzyme modulation, allow rapid adjustment of the amount of active species to the actual requirements. The structural basis of the regulation of chloroplast NADP+ -malate dehydrogenase (EC 1.1.1.82) is described in more detail. The modulable plastid enzyme is characterized by two sequence extensions not present in any other known NADP+ - and/or NAD+ -specific malate dehydrogenase. The NADP+ -malate dehydrogenase of C3 -plants is part of the "malate valve", which catalyzes the export of reducing equivalents in the form of malate from the chloroplast only when the NADPH to NADP+ ratio is high, thus poising the NADPH to ATP ratio required for optimal carbon reduction in the light. The mode of regulation of other light/dark modulated enzymes is discussed. 相似文献
20.
The growth response of C4 plants to rising atmospheric CO2 partial pressure: a reassessment 总被引:1,自引:2,他引:1
O. Ghannoum S. Von Caemmerer L. H. Ziska & J. P. Conroy 《Plant, cell & environment》2000,23(9):931-942
Despite mounting evidence showing that C4 plants can accumulate more biomass at elevated CO2 partial pressure (p(CO2)), the underlying mechanisms of this response are still largely unclear. In this paper, we review the current state of knowledge regarding the response of C4 plants to elevated p(CO2) and discuss the likely mechanisms. We identify two main routes through which elevated p(CO2) can stimulate the growth of both well-watered and water-stressed C4 plants. First, through enhanced leaf CO2 assimilation rates due to increased intercellular p(CO2). Second, through reduced stomatal conductance and subsequently leaf transpiration rates. Reduced transpiration rates can stimulate leaf CO2 assimilation and growth rates by conserving soil water, improving shoot water relations and increasing leaf temperature. We argue that bundle sheath leakiness, direct CO2 fixation in the bundle sheath or the presence of C3-like photosynthesis in young C4 leaves are unlikely explanations for the high CO2-responsiveness of C4 photosynthesis. The interactions between elevated p(CO2), leaf temperature and shoot water relations on the growth and photosynthesis of C4 plants are identified as key areas needing urgent research. 相似文献