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 15 毫秒
1.
The ion-exchange properties of cell wall polymers isolated from the roots of wheat (Triticum aestivum L.) plants grown on either nitrate-free (N-deficient) or nitrate-containing (+N) hydroponic nutrient medium have been investigated. Irrespective of the nitrogen nutrition regimen, the studied cell walls contained four types of ion-exchange groups: primary amino groups of structural proteins (pKa < 3), carboxyl groups of polygalacturonic acid in pectin (pK a ~4.7), carboxyl groups of hydroxycinnamic acids (pK a ~7.3), and phenolic OH-groups of lignin (pKa ~10.2). The quantitative ratio between these types of ion-exchange groups, the mass fraction of cell walls in the dry weight of roots, and the swelling coefficient of cell walls depended on the nitrate presence in the growing medium. Compared to the +N variant, the N-deficient variant was characterized by a 2.4 times higher content of phenolic OH-groups in cell walls and 1.24 times higher mass fraction of cell walls; at the same time, the swelling coefficient for this variant was lower by 10%. The obtained data indicate that nitrogen deficiency results in a formation of thicker root cell walls with a higher degree of polymer cross-linking that may be caused by the increased lignin content.  相似文献   

2.
A new anti-Prelog short-chain dehydrogenase/reductase (SDR) encoding gene lcsdr was cloned from Lactobacillus composti DSM 18527, and heterologously expressed in Escherichia coli. LcSDR is nicotinamide adenine dinucleotide phosphate (NADPH)-dependent and has a molecular weight of approximately 30 kDa. The optimal pH and temperature were 6.5 and 30?°C, respectively. The maximal reaction rate Vmax was 133.9 U mg?1; the Michaelis–Menten constant K m of LcSDR were 0.345 mM for acetophenone (1a), and 0.085 mM for NADPH. Through introducing an EsGDH-catalyzed NADPH regeneration system, a biocatalytic process for (R)-1-phenylethanol ((R)-1b) was developed with outstanding time–space yield. Under the optimized conditions, 50 g l?1 1a was converted to (R)-1b in 2 h with a yield of 93.8%, enantiomeric excess of product (e.e.p) above 99% and space–time yield of 562.8 g l?1 d?1.  相似文献   

3.
4.
An extracellular feruloyl esterase from the culture filtrates of the isolated fungus Alternaria tenuissima was successfully purified to apparent homogeneity by anion-exchange and size-exclusion chromatography. Peptide fragments of purified enzyme (designated as AltFAE; molecular weight of 30.3 kDa determined by SDS-PAGE) were identified by mass spectrometry using a NanoLC-ESI-MS/MS system. Michaelis-Menten constants (KM) and catalytic efficiencies (kcat/KM) were determined for typical substrates of feruloyl esterase, and the lowest KM of 50.6 μM (i.e., the highest affinity) and the highest kcat/KM (3.1 × 105 s—1 M–1) were observed for methyl p-coumarate and methyl ferulate, respectively. Not least, AltFAE catalyzed conversion of lignocellulosic material (e.g. wood meal) to release hydroxycinnamic products, i.e. ferulic- and p-coumaric acids.  相似文献   

5.
Expression of acid ectophosphatase by Enterobacter asburiae, isolated from Cattleya walkeriana (Orchidaceae) roots and identified by the 16S rRNA gene sequencing analysis, was strictly regulated by phosphorus ions, with its optimal activity being observed at an inorganic phosphate concentration of 7 mM. At the optimum pH 3.5, intact cells released p-nitrophenol at a rate of 350.76 ± 13.53 nmol of p-nitrophenolate (pNP)/min/108 cells. The membrane-bound enzyme was obtained by centrifugation at 100,000 × g for 1 h at 4°C. p-Nitrophenylphosphate (pNPP) hydrolysis by the enzyme follows “Michaelis-Menten” kinetics with V = 61.2 U/mg and K0.5 = 60 μM, while ATP hydrolysis showed V = 19.7 U/mg, K0.5 = 110 μM, and nH = 1.6 and pyrophosphate hydrolysis showed V = 29.7 U/mg, K0.5 = 84 μM, and nH = 2.3. Arsenate and phosphate were competitive inhibitors with Ki = 0.6 mM and Ki = 1.8 mM, respectively. p-Nitrophenyl phosphatase (pNPPase) activity was inhibited by vanadate, while p-hydroxymercuribenzoate, EDTA, calcium, copper, and cobalt had no inhibitory effects. Magnesium ions were stimulatory (K0.5 = 2.2 mM and nH = 0.5). Production of an acid ectophosphatase can be a mechanism for the solubilization of mineral phosphates by microorganisms such as Enterobacter asburiae that are versatile in the solubilization of insoluble minerals, which, in turn, increases the availability of nutrients for plants, particularly in soils that are poor in phosphorus.  相似文献   

6.
We examined changes in suspended-sediment yields (SSY) after a 50 % strip thinning in headwater streams draining a Japanese cedar (Cryptomeria japonica) and cypress (Chamaecyparis obtusa) plantation forest. We applied a paired-catchment analysis to treated (K T : 17.1 ha) and control (K C : 8.9 ha) catchments. Annual suspended-sediment yield (SSYan) in the prethinning period in the K T and K C catchments was 110.0 and 142.1 kg/ha per year. For the postthinning period, SSYan in the K T catchment became 5055.6 kg/ha per year, whereas that in the K C catchment increased 893.2 kg/ha per year. The paired-catchment analysis revealed that SSY in the K T catchment increased 17.0-fold compared with the prethinning period. However, the dominant hysteresis pattern remained clockwise in both pre- and postthinning periods. Sequences of large storm events in the postthinning period elevated SSY in both catchments. Increase in suspended sediment in the K T catchment was associated with the combined impacts of thinning and sequences of storm events during the period of thinning operation.  相似文献   

7.
A total of 18 polymorphic microsatellite loci were isolated and characterized from RAPD products in the Xinjiang Arctic Grayling (Thymallus arcticus grubei). The number of alleles (Na) per locus varied from 2 to 10. Observed (Ho) and expected (He) heterozygosities ranged from 0.64 to 0.92, and from 0.63 to 0.88, respectively. Considerable differences were found among HBH, FH and FY populations in the number of alleles, effective number of alleles, number of genotypes at all of these loci. These new RAPD-SSR markers have provided a helpful tool for genetic analyses and resources conservation of T. arcticus grubei. Five additional fish species, Amur grayling (Thymallus grubii), Taimen (Hucho taimen), Sea perch (Lateolabrax japonicus), Lenok (Brachymystax lenok) and Red seam bream (Pagrosomus major) were assessed for cross-species amplification. Three of the five species showed at least one polymorphic locus. In addition, seven loci were found to be polymorphic in at least one species.  相似文献   

8.
Studies of substrate specificity revealed that the D-aminoacylase of Rhodococcus armeniensis AM6.1 strain exhibits absolute stereospecificity to the D-stereoisomers of N-acetyl-amino acids. The enzyme is the most active reacted with N-acetyl-D-methionine, as well as with aromatic and hydrophobic N-acetylamino acids and interacts weakly with the basic substrates. It is practically not reacted with acidic and hydrophilic N-acetyl-amino acids. Michaelis constants (Km) and maximum reaction velocities (Vmax) were calculated, using linear regression analysis, for the following substrates: N-acetyl-D-methionine, N-acetyl-D-alanine, N-acetyl-D-phenylalanine, N-acetyl-D-tyrosine, N-acetyl-D-valine, N-acetyl-D-oxyvaline, N-acetyl- D-leucine. Substrate inhibition of D-aminoacylase was displayed with N-acetyl-D-leucine (Ks = 35.5 ± 28.3 mM) and N-acetyl-DL-tyrosine (Ks = 15.8 ± 4.5 mM). Competitive inhibition of the enzyme with product–acetic acid (Ki = 104.7 ± 21.7 mM, Km = 2.5 ± 0.5 mM, Vmax = 25.1 ± 1.5 U/mg) was observed.  相似文献   

9.
The different role of coat color mutations in the American mink on the per os effect of the biologically active preparation Biostyl was shown. The number of kits per female was the same in all control genotypes, including Standard (+/+ +/+), sapphire (a/a p/p), and lavender (a/a m/m): 4.4 ± 0.4, 4.4 ± 0.5, and 4.3 ± 0.5, respectively. Experimental groups of these genotypes have shown a great contrast among each other: stimulation of the reproductive function was 5.2 ± 0.3 in Standard minks, while suppression of the reproductive function was 3.8 ± 0.6, and 2.3 ± 0.5 in the double recessive mutants sapphire and lavender, respectively. The differentiation in body mass between experimental and control newborn Standard kits was not revealed. A significant decrease in the body mass of newborn experimental sapphire kits as compared to control group in a sex-specific manner was registered.  相似文献   

10.
On the basis of the winter bread wheat cultivar Obryi, two independent disomic addition lines BC12F with the chromosome of the E. sibiricus St genome are created. A practical algorithm for determining the probabilities of transmission of the odd chromosome separately through male and female gametes in selfpollination of hemizygous hybrids from the equation p2–(1 + f1f4) × p + f1 = 0 is proposed, where p is the probability of the formation of viable gametes with the considered chromosome and f1 and f4 are the empirical frequencies of the corresponding homozygotes with and without the trait. The probability of transmission of an alien univalent chromosome through pollen (p) is associated with the frequency of its transmission through the egg cell (p) in backcrosses and in self-pollination (1–f4) by the equation p = 1–f4/(1–p). The calculated empirically dependent estimates of the probabilities of transmission of the added chromosome through the egg cell p = 18.7% and through pollen p = 4.3% correspond to the empirical frequencies obtained for backcrosses. The coefficients of the gamete selection V = 0.748 and V = 0.172 are calculated, and the expected segregation for the alien trait controlled by a dominant gene located in the added chromosome is determined—with the trait: without the trait is 0.222: 0.778 in F2; 0.187: 0.813 in equational and 0.043: 0.957 in certational backcrosses.  相似文献   

11.

Objectives

To prepare (R)-phenyl-1,2-ethanediol ((R)-PED) with high enantiomeric excess (ee p) and yield from racemic styrene oxide (rac-SO) at high concentration by bi-enzymatic catalysis.

Results

The bi-enzymatic catalysis was designed for enantioconvergent hydrolysis of rac-SO by a pair of novel epoxide hydrolases (EHs), a Vigna radiata EH3 (VrEH3) and a variant (AuEH2A250I) of Aspergillus usamii EH2. The simultaneous addition mode of VrEH3 and AuEH2A250I, exhibiting the highest average turnover frequency (aTOF) of 0.12 g h?1 g?1, was selected, by which rac-SO (10 mM) was converted into (R)-PED with 92.6% ee p and 96.3% yield. Under the optimized reaction conditions: dry weight ratio 14:1 of VrEH3-expressing E. coli/vreh3 to AuEH2A250I-expressing E. coli/Aueh2 A250I and reaction at 20 °C, rac-SO (10 mM) was completely hydrolyzed in 2.3 h, affording (R)-PED with 98% ee p. At the weight ratio 0.8:1 of rac-SO to two mixed dry cells, (R)-PED with 97.4% ee p and 98.7% yield was produced from 200 mM (24 mg/ml) rac-SO in 10.5 h.

Conclusions

Enantioconvergent hydrolysis of rac-SO at high concentration catalyzed by both VrEH3 and AuEH2A250I is an effective method for preparing (R)-PED with high ee p and yield.
  相似文献   

12.
A series of novel 2-(chromon-3-yl)-4,5-diphenyl-1H-imidazoles (4a-h) were synthesized by one pot condensation of substituted 3-formylchromones (1a-h), benzil (2) and ammonium acetate (3) in refluxing acetic acid at 110 °C under N2 atmosphere. Allylation of compounds 4a-h with allyl bromide in the presence of fused K2CO3 furnished N-allyl-2-(chromon-3-yl)-4,5-diphenyl-1H-imidazoles (6a-h). The synthesized compounds were characterized spectroscopically and evaluated for in vitro antimicrobial activity against various pathogenic bacterial and fungal strains by disc diffusion method. Compounds bearing electron withdrawing substituents such as bromo (4f) showed significant inhibitory activity against S. cerevisiae (MIC 1.4 μg/ml) and 4g containing chloro substituent, displayed more inhibitory potential against C. albicans (MIC 1.5), as compared to the standard drugs. Compounds 6a and 4c exhibit remarkable inhibitory potential against B. subtilis with MIC 0.98 and 1.23, respectively. The time kill assay for active compound 6a was performed by viable cell count (VCC) method to elucidate the microbicidal nature of 2-(chromon-3-yl)imidazoles. A molecular docking study of most active compounds with target ‘lanosterol 14α-demethylase’ (CYP51) was performed to unravel the mode of antifungal action.  相似文献   

13.
An efficient ß-1,4-glucosidase (BGL) producing strain, Fomitopsis pinicola KMJ812, was isolated and identified based on morphological features and sequence analysis of internal transcribed spacer rDNA. An extracellular BGL was purified to homogeneity by sequential chromatography of F. pinicola culture supernatants on a DEAE-sepharose column, a gel filtration column, and then on a Mono Q column with fast protein liquid chromatography. The relative molecular weight of F. pinicola BGL was determined to be 105 kDa by sodium dodecylsulfate-polyacrylamide gel electrophoresis, or 110 kDa by size exclusion chromatography, indicating that the enzyme is a monomer. The hydrolytic activity of the BGL had a pH optimum of 4.5 and a temperature optimum of 50°C. The enzyme showed high substrate specificity and high catalytic efficiency (k cat?=?2,990 s?1, K m?=?1.76 mM, k cat/K m?=?1,700 mM?1 s?1) for p-nitrophenyl-β-d-glucopyranoside. Its internal amino acid sequences showed a significant homology with hydrolases from glycoside hydrolase family 3, indicating that the F. pinicola BGL is a member of glycoside hydrolase family 3. Although BGLs have been purified and characterized from several other sources, F. pinicola BGL is distinguished from other BGLs by its high catalytic efficiency and strict substrate specificity.  相似文献   

14.
The Caulobacter crescentus (NA1000) xynB5 gene (CCNA_03149) encodes a predicted β-glucosidase-β-xylosidase enzyme that was amplified by polymerase chain reaction; the product was cloned into the blunt ends of the pJet1.2 plasmid. Analysis of the protein sequence indicated the presence of conserved glycosyl hydrolase 3 (GH3), β-glucosidase-related glycosidase (BglX) and fibronectin type III-like domains. After verifying its identity by DNA sequencing, the xynB5 gene was linked to an amino-terminal His-tag using the pTrcHisA vector. A recombinant protein (95 kDa) was successfully overexpressed from the xynB5 gene in E. coli Top 10 and purified using pre-packed nickel-Sepharose columns. The purified protein (BglX-V-Ara) demonstrated multifunctional activities in the presence of different substrates for β-glucosidase (pNPG: p-nitrophenyl-β-D-glucoside) β-xylosidase (pNPX: p-nitrophenyl-β-D-xyloside) and α-arabinosidase (pNPA: p-nitrophenyl-α-L-arabinosidase). BglX-V-Ara presented an optimal pH of 6 for all substrates and optimal temperature of 50 °C for β-glucosidase and α-l-arabinosidase and 60 °C for β-xylosidase. BglX-V-Ara predominantly presented β-glucosidase activity, with the highest affinity for its substrate and catalytic efficiency (Km 0.24 ± 0.0005 mM, Vmax 0.041 ± 0.002 µmol min?1 mg?1 and Kcat/Km 0.27 mM?1 s?1), followed by β-xylosidase (Km 0.64 ± 0.032 mM, Vmax 0.055 ± 0.002 µmol min?1 mg?1 and Kcat/Km 0.14 mM?1s?1) and finally α-l-arabinosidase (Km 1.45 ± 0.05 mM, Vmax 0.091 ± 0.0004 µmol min?1 mg?1 and Kcat/Km 0.1 mM?1 s?1). To date, this is the first report to demonstrate the characterization of a GH3-BglX family member in C. crescentus that may have applications in biotechnological processes (i.e., the simultaneous saccharification process) because the multifunctional enzyme could play an important role in bacterial hemicellulose degradation.  相似文献   

15.
Thermal preference is one of the most crucial components of behavioral thermoregulation in ectotherms, and documenting the adaptation of thermal preference carries great importance for studying the evolution of thermal biology. However there are not many studies focusing on the adaptation of thermal preference in elevational and latitudinal gradients. Isophya rizeensis is a color polymorphic bush cricket species endemic to the mountainous region of northeastern Turkey. Populations of this species are distributed in a wide elevational range between 350 and 2300 m. In this study, we hypothesized that the thermal preference of Isophya rizeensis might follow a countergradient variation where crickets from higher altitudes have higher temperature preferences compared to crickets from lower altitudes. To test this hypothesis, thermal preference values (T pref ) of crickets from three altitudes groups (low, middle and high) were measured with a thermal gradient experiment. Additionally, body temperatures (T b ) and environmental temperatures (T a ) were measured in field. Deviation values of T b and T a from T pref were calculated to investigate the extent of thermoregulation. As Isophya rizeensis is color polymorphic species where morphology pattern changes from lighter to darker types with increasing altitude we also tested whether coloration has any effect on temperature excess (T ex ) and thermoregulation. Thermal preference values did not differ significantly between three groups and also colouration does not influence the extent of thermoregulation in this species. These results indicate that there is not sufficient evidence for the existence of a countergradient selection related with thermal behavior. However, the deviation of body (D b ) and environmental (D a ) temperatures suggest that at higher altitudes thermoregulation might be more efficient than lower altitudes.  相似文献   

16.
Understanding the environmental impact of bioenergy crops is needed to inform bioenergy policy development. We determined the effects of five biomass cropping systems—continuous maize (Zea mays), soybean (Glycine max)-triticale (Triticosecale ×)/soybean-maize, maize-switchgrass (Panicum virgatum), triticale/sorghum (Sorghum bicolor), and triticale-aspen (Populus alba × P. grandidentata)—on soil-saturated hydraulic conductivity (K S ) across a toposequence in central Iowa, USA. We compared data from the time of cropping system establishment in 2009 to 4 years post-establishment. Both our 2009 and 2013 data confirmed that cropping system impacts on K S vary by landscape position. We found that differences in cropping system impacts were more likely to occur at lower landscape positions, specifically, within footslope and floodplain positions. Previous research on cropping system impacts suggested that grass and woody systems were associated with a general increase in K S over time, with greater changes likely occurring at landscape positions with a higher erosive potential or lower SOC content. Our results confirmed that the triticale-aspen woody system was associated with a significant increase in K S across all landscape positions. In contrast, we did not observe an increase in K S under maize-switchgrass, which we attributed to the high density of switchgrass roots by the fourth year of study, but expect an increase in K S under switchgrass under longer measurement periods. We also found a significant increase in K S in the annual systems, likely due to the conversion to no-till soil management with cropping system establishment. We expect such differences to become more apparent over longer time scales as cropping systems continue to impact soil hydraulic properties.  相似文献   

17.
Powdery mildew caused by Erysiphe euonymi-japonici (Eej) is an increasingly serious fungal disease on Euonymus japonicus that is an important ornamental plant. However, little is currently known about infection and pathogenesis of Eej on E. japonicus. Here, we report plant infection by Eej at the histological and cytological levels. Eej caused severe disease symptoms with white and snow-like colonies on leaf surfaces of E. japonicus. Microscopic observations were conducted continuously to define infection process of Eej on E. japonicus. Eej conidia germinated to produce appressorial germ tubes on leaf surfaces and formed irregular haustoria in plant epidermal cells at 6 h post-inoculation (hpi) and 12 hpi, respectively. After uptaking nutrients from host cells by haustoria, Eej formed numerous hyphae and extensive colonization on leaf surfaces at 96 hpi and finally produced abundant conidiophores and new conidia on leaf surfaces at 168 hpi. In addition, there was consistently a single nucleus in different Eej infection structures and haustorial development could be divided into three major stages, including formation of penetration peg, formation of haustorial neck and initial haustorium, and maturation of haustorium. These results provide useful information for further determination of Eej pathogenesis and finally controlling the disease.  相似文献   

18.
Higher plant hydraulic conductivity (K plant) is vital for plant growth, especially under PEG-induced water deficit stress (PEG-IWDS). Leaf venation architecture is a key determinant of leaf hydraulic conductivity (K leaf) and K leaf is a major component of K plant across different plant species. However, there is little information about (1) varietal difference in leaf vein development in cereal crops, such as rice plants; (2) the effects of PEG-IWDS on leaf vein development; (3) the coordination between leaf venation architecture and K plant as well as K leaf under PEG-IWDS. In the present study, widely cultivated eight rice cultivars were grown hydroponically under well-watered condition (WWC) and PEG-IWDS, simulated by adding 15 % (w/v) PEG6000. Leaf venation architecture, including total longitudinal leaf vein number, leaf vein numbers per unit width (LVNW), vein thickness and leaf mass per area, as well as K plant and K leaf were measured to address above-mentioned questions. The results showed that leaf venation architecture exhibited significant varietal differences and PEG-IWDS significantly increased LVNW while decreased vein thickness. PEG-IWDS suppressed both K plant and K leaf but the decrease was much higher in K plant than K leaf. There was a significant and positive correlation observed between LVNW and K leaf under both WWC and PEG-IWDS but the correlation between LVNW and K plant was only significant under WWC. K leaf was significantly and positively correlated with K plant under WWC but not under PEG-IWDS. It is concluded that K leaf is a major determinant for K plant under WWC but not under PEG-IWDS; therefore, breeding or selecting rice cultivars with high LVNW can improve shoot water supplement under WWC but not under PEG-IWDS condition.  相似文献   

19.
A 1.4 Kb fragment of Bacillus licheniformis ATCC 14580 encoding β-glucosidase was cloned and expressed in Escherichia coli. β-Glucosidase expressed by E. coli harboring cloned gene was located entirely in the intracellular fraction. Recombinant β-glucosidase protein was purified to homogeneity level and the molecular weight was found to be 53 kDa using sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis. It gave maximum activity at 50°C and pH 6. K m and V max were 0.206 mM and 1.26 U/mg, respectively, with p-nitrophenyl-β-D-glucopyranoside, while activation energy Ea, enthalpy of activation ?H and entropy of activation ΔS were found to be 66.31 kJ/mol, 64.04 kJ/mol and 48.28 J/mol/K, respectively. The pKa1 and pKa2 of the ionizable groups of active site residues involved in Vmax were found to be 5.5 and 7.0, respectively. When the recombinant β-glucosidase protein was used as a member of consortium with endoglucanase and exoglucanase for the saccharification of wheat straw, 123% increase in saccharification was observed.  相似文献   

20.
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