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981.
Two quinones, stereochenols A (1) and B (2) were isolated from a methanol extract of the stem bark of Stereospermum chelonoides, in addition to the known naphthoquinones, sterekunthal B (3) and sterequinone C (4). The structures of these compounds were established by extensive spectroscopic analyses and by comparison of their spectral data with those of related compounds. 相似文献
982.
Bresolin NS Li Z Kosar-Hashemi B Tetlow IJ Chatterjee M Rahman S Morell MK Howitt CA 《Planta》2006,224(1):20-31
Disproportionating enzyme or D-enzyme (EC 2.4.1.25) is an α-1,4 glucanotransferase which catalyses cleavage and transfer reactions involving α-1,4 linked glucans altering (disproportionating) the chain length distribution of pools of oligosaccharides. While D-enzyme has been well characterised in some plants, e.g. potato and Arabidopsis, very little is known about its abundance and function in cereals which constitute the major source of starch worldwide. To address this we have investigated D-enzyme in wheat (Triticum aestivum). Two putative D-enzyme cDNA clones have been isolated from tissue-specific cDNA libraries. TaDPE1-e, from an endosperm cDNA library, encodes a putative polypeptide of 575 amino acid residues including a predicted transit peptide of 41 amino acids. The second cDNA clone, TaDPE1-l, from an Aegilops taushii leaf cDNA library, encodes a putative polypeptide of 579 amino acids including a predicted transit peptide of 45 amino acids. The mature polypeptides TaDPE1-e and TaDPE1-l were calculated to be 59 and 60 kDa, respectively, and had 96% identity. The putative polypeptides had significant identity with deduced D-enzyme sequences from corn and rice, and all the expected conserved residues were present. Protein analysis revealed that D-enzyme is present in the amyloplast of developing endosperm and in the germinating seeds. D-enzyme was partially purified from wheat endosperm and shown to exhibit disproportionating activity in vitro by cleaving maltotriose to produce glucose as well as being able to use maltoheptaose as the donor for the addition of glucans to the outer chains of glycogen and amylopectin. 相似文献
983.
984.
Moien-Afshari F Ghosh S Elmi S Khazaei M Rahman MM Sallam N Laher I 《American journal of physiology. Heart and circulatory physiology》2008,295(4):H1470-H1480
Regulation of coronary function in diabetic hearts is an important component in preventing ischemic cardiac events but remains poorly studied. Exercise is recommended in the management of diabetes, but its effects on diabetic coronary function are relatively unknown. We investigated coronary artery myogenic tone and endothelial function, essential elements in maintaining vascular fluid dynamics in the myocardium. We hypothesized that exercise reduces pressure-induced myogenic constriction of coronary arteries while improving endothelial function in db/db mice, a model of type 2 diabetes. We used pressurized mouse coronary arteries isolated from hearts of control and db/db mice that were sedentary or exercised for 1 h/day on a motorized exercise-wheel system (set at 5.2 m/day, 5 days/wk). Exercise caused a approximately 10% weight loss in db/db mice and decreased whole body oxidative stress, as measured by plasma 8-isoprostane levels, but failed to improve hyperglycemia or plasma insulin levels. Exercise did not alter myogenic regulation of arterial diameter stimulated by increased transmural pressure, nor did it alter smooth muscle responses to U-46619 (a thromboxane agonist) or sodium nitroprusside (an endothelium-independent dilator). Moderate levels of exercise restored ACh-simulated, endothelium-dependent coronary artery vasodilation in db/db mice and increased expression of Mn SOD and decreased nitrotyrosine levels in hearts of db/db mice. We conclude that the vascular benefits of moderate levels of exercise were independent of changes in myogenic tone or hyperglycemic status and primarily involved increased nitric oxide bioavailability in the coronary microcirculation. 相似文献
985.
Alam MS Igawa T Khan MM Islam MM Kuramoto M Matsui M Kurabayashi A Sumida M 《Molecular phylogenetics and evolution》2008,48(2):515-527
To elucidate the species composition, genetic divergence, evolutionary relationships, and divergence time of Hoplobatrachus and Euphlyctis frogs (subfamily Dicroglossinae, family Ranidae) in Bangladesh and other Asian countries, we analyzed the mitochondrial Cyt b, 12S, and 16S rRNA genes of 252 specimens. Our phylogenetic analyses showed 13 major clades corresponding to several cryptic species as well as to nominal species in the two genera. The results suggested monophyly of Asian Hoplobatrachus species, but the position of African Hoplobatrachus occipitalis was not clarified. Nucleotide divergence and phylogenetic data suggested the presence of allopatric cryptic species allied to Euphlyctis hexadactylus in Sundarban, Bangladesh and several parapatric cryptic species in the Western Ghats, India. The presence of at least two allopatric cryptic species among diverged Euphlyctis cyanophlyctis in Bangladesh, India, and Sri Lanka was also suggested. In some cases, our estimated divergence times matched the paleogeological events of South and Southeast Asian regions that may have led to the divergence of Hoplobatrachus and Euphlyctis taxa. Especially, land formation at Bangladesh (15–10 Ma) may have allowed the spread of these frog taxa to Southeast Asian areas, and the aridification of central India (5.1–1.6 Ma) might have affected the gene flow of widely distributed species. The present study revealed prior underestimation of the richness of the amphibian fauna in this region, indicating the possible occurrence of many cryptic species among these groups. 相似文献
986.
Md. Morshedur Rahman Woan-Sub Kim Haruto Kumura Kei-ichi Shimazaki 《World journal of microbiology & biotechnology》2008,24(8):1593-1598
Thirteen strains of four different Bifidobacterium spp. were observed for their autoaggregation ability and surface hydrophobicity, and correlation between these two traits
was determined. Bifidobacteria were classified into high, medium and low autoaggregation strains according to autoaggregation
ratio measured from changes in absorbance of media. High autoaggregation strains showed microscopic clustering of cells, whereas
low and medium autoaggregation strains showed no such clustering. Autoaggregation ability decreased in high autoaggregation
strains but increased in medium and low autoaggregation strains when the assay was performed at higher temperature (37°C compared
with 25 and 10°C). Bacterial strains belonging to the high, medium or low autoaggregation group were correlated in terms of
their surface hydrophobicity and evaluated based on changes in absorbance of the bacterial suspension before and after extraction
with xylene. These results indicate that autoaggregation ability, together with surface hydrophobicity and microscopic image
could be used for evaluating the adhesion ability of potential probiotic bifidobacterial strains. Moreover, a synergistic
effect of pH and media may be involved in autoaggregation. 相似文献
987.
Keng PS Basri M Ariff AB Abdul Rahman MB Abdul Rahman RN Salleh AB 《Bioresource technology》2008,99(14):6097-6104
Lipase-catalyzed production of palm esters by alcoholysis of palm oil with oleyl alcohol in n-hexane was performed in 2L stirred-tank reactor (STR). Investigation on the performance of reactor operation was carried out in batch mode STR with single impeller mounted on the centrally located shaft. Rushton turbine (RT) impellers provide the highest reaction yield (95.8%) at lower agitation speed as compared to AL-hydrofoil (AL-H) and 2-bladed elephant ear (EE) impellers. Homogenous enzyme particles suspension was obtained at 250 rpm by using RT impeller. At higher impeller speed, the shear effect on the enzyme particles caused by agitation has decreased the reaction performance. Palm esters reaction mixture in STR follows Newtons' law due to the linear relation between the shear stress (tau) and shear rate (dupsilon/dy). High stability of Lipozyme RM IM was observed as shown by its ability to be repeatedly used to give high percentage yield (79%) of palm esters even after 15 cycles of reaction. The process was successfully scale-up to 75 L STR (50 L working volume) based on a constant impeller tip speed approach, which gave the yield of 97.2% after 5h reaction time. 相似文献
988.
Younesi H Najafpour G Ku Ismail KS Mohamed AR Kamaruddin AH 《Bioresource technology》2008,99(7):2612-2619
Hydrogen may be considered a potential fuel for the future since it is carbon-free and oxidized to water as a combustion product. Bioconversion of synthesis gas (syngas) to hydrogen was demonstrated in continuous stirred tank bioreactor (CSTBR) utilizing acetate as a carbon source. An anaerobic photosynthetic bacterium, Rhodospirillum rubrum catalyzed water-gas shift reaction which was applied for the bioconversion of syngas to hydrogen. The continuous fermentation of syngas in the bioreactor was continuously operated at various gas flow rates and agitation speeds, for the period of two months. The gas flow rates were varied from 5 to 14 ml/min. The agitation speeds were increasingly altered in the range of 150-500 rpm. The pH and temperature of the bioreactor was set at 6.5 and 30 degrees C. The liquid flow rate was kept constant at 0.65 ml/min for the duration of 60 days. The inlet acetate concentration was fed at 4 g/l into the bioreactor. The hydrogen production rate and yield were 16+/-1.1 mmol g(-1)cell h(-1) and 87+/-2.4% at fixed agitation speed of 500 rpm and syngas flow rate of 14 ml/min, respectively. The mass transfer coefficient (KLa) at this condition was approximately 72.8h(-1). This new approach, using a biocatalyst was considered as an alternative method of conventional Fischer-Tropsch synthetic reactions, which were able to convert syngas into hydrogen. 相似文献
989.
Potential water quality impacts associated with using bottom ash (BA) and composted dairy manure (CM) as a soil amendment were evaluated in this study. Two column studies were conducted to evaluate three blends of acidic BA and CM (BA:CM, v/v) namely, B1ac (95:5), B2ac (90:10), and B3ac (80:20) and three blends of alkaline BA and CM (BA:CM, v/v), namely, B1al (95:5), B2al (90:10), and B3al (80:20) under constant head water table conditions. Samples from standing water (top) and leachate (bottom) were collected at weekly intervals until day 49 to evaluate the effects of different blend ratios and elapsed time on standing water and leachate chemical and physical properties. A higher CM content in both acidic and alkaline blends resulted in higher leachate concentrations for solids and nutrients tested in this study. Alkaline blends had higher standing water and leachate nutrients concentration compared to acidic blends. After day 28, standing water total dissolved solids (TDS) concentrations for all acidic blends was below the USEPA drinking water standard however, TDS value for alkaline blend was always below the standard. Similar trends were also observed for NO3–N and phosphorus (P) concentrations for both blends. Based on these findings, it was concluded that acidic and alkaline blends B1ac, B1al, B2ac and B2al may be considered as a soil amendment material. 相似文献
990.
Alpha-glucan phosphorylase catalyzes the reversible cleavage of
α-1-4-linked glucose polymers into α-D-glucose-1-phosphate.
We report the recombinant production of an α-glucan/maltodextrin
phosphorylase (PF1535) from a hyperthermophilic archaeon,
Pyrococcus furiosus, and the first detailed
biochemical characterization of this enzyme from any archaeal source
using a mass-spectrometry-based assay. The apparent 98 kDa recombinant
enzyme was active over a broad range of temperatures and pH, with
optimal activity at 80 °C and pH 6.5–7. This archaeal
protein retained its complete activity after 24 h at 80 °C in
Tris-HCl buffer. Unlike other previously reported phosphorylases, the
Ni-affinity column purified enzyme showed broad substrate specificity
in both the synthesis and degradation of maltooligosaccharides. In the
synthetic direction of the enzymatic reaction, the lowest
oligosaccharide required for the chain elongation was maltose. In the
degradative direction, the archaeal enzyme can produce
glucose-1-phosphate from maltotriose or longer maltooligosaccharides
including both glycogen and starch. The specific activity of the
enzyme at 80 °C in the presence of 10 mM maltoheptaose and at 10
mg ml–1 glycogen concentration was 52 U
mg–1 and 31 U mg–1, respectively.
The apparent Michaelis constant and maximum velocity for inorganic
phosphate were 31 ± 2 mM and 0.60 ± 0.02 mM
min–1 µg–1, respectively. An
initial velocity study of the enzymatic reaction indicated a
sequential bi-bi catalytic mechanism. Unlike the more widely studied
mammalian glycogen phosphorylase, the Pyrococcus
enzyme is active in the absence of added AMP. 相似文献