排序方式: 共有99条查询结果,搜索用时 31 毫秒
81.
Mishela Temkov Aleksandar Petrovski Emilija Gjorgieva Emil Popovski Maja Lazarova Ivan Boev Perica Paunovic Anita Grozdanov Aleksandar Dimitrov Aliaksandr Baidak Albert Krastanov 《Engineering in Life Science》2019,19(9):617-630
This paper describes the development of a simple method for mixed non‐covalent and covalent bonding of partially purified inulinase on functionalized multiwall carbon nanotubes (f‐MWCNTs) with polypyrrole (PPy). The pyrrole (Py) was electrochemically polymerized on MWCNTs in order to fabricate MWCNTs/PPy nanocomposite. Two multiple forms of enzyme were bound to N‐H functional groups from PPy and ‐COO? from activated MWCNTs to yield a stable MWCNTs/PPy/PEG immobilized preparation with increased thermal stability. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) were used to confirm functionalization of nanoparticles and immobilization of the enzyme. The immobilization yield of 85% and optimal enzyme load of 345 μg protein onto MWCNTs was obtained. The optimum reaction conditions and kinetic parameters were established using the UV‐Vis analytical assay. The best functional performance for prepared heterogeneous catalyst has been observed at pH 3.6 and 10, and at the temperatures of 60 and 80ºC. The half‐life (t1/2) of the immobilized inulinase at 60 and 80ºC was found to be 231 and 99 min, respectively. The reusability of the immobilized formulation was evaluated based on a method in which the enzyme retained 50% of its initial activity, which occurred after the eighteenth operation cycle. 相似文献
82.
83.
Anna Aronovich Dalit Tchorsh Elias Shezen Chava Rosen Yael Klionsky Sivan Cohen Orna Tal Uri Martinowitz Helena Katchman Smadar Eventov-Friedman Ninette Amariglio Jasmine Jacob-Hirsch Gideon Rechavi Yair Reisner 《PloS one》2009,4(12)
Very little is known about the mechanisms that contribute to organ size differences between species. In the present study, we used a mouse model of embryonic pig tissue implantation to define the role of host Factor VIII in controlling the final size attained by the implant. We show here that pig embryonic spleen, pancreas, and liver all grow to an increased size in mice that are deficient in the Factor VIII clotting cascade. Similar results were obtained using the transplantation model after treatment with the low molecular weight heparin derivative Clexane which markedly enhanced transplant size. Likewise, enhanced size was found upon treatment with the direct thrombin inhibitor Dabigatran, suggesting that organ size regulation might be mediated by thrombin, downstream of Factor VIII. Considering that thrombin was shown to mediate various functions unrelated to blood clotting, either directly by cleavage of protease-activated receptors (PARs) or indirectly by cleaving osteopontin (OPN) on stroma cells, the role of PAR1 and PAR4 antagonists as well as treatment with cleaved form of OPN (tcOPN) were tested. While the former was not found to have an impact on overgrowth of embryonic pig spleen implants, marked reduction of size was noted upon treatment with the (tcOPN). Collectively, our surprising set of observations suggests that factors of the coagulation cascade have a novel role in organ size control. 相似文献
84.
Association mapping of leaf rust response in durum wheat 总被引:1,自引:0,他引:1
Marco Maccaferri Maria C. Sanguineti Paola Mantovani Andrea Demontis Andrea Massi Karim Ammar James A. Kolmer Jerzy H. Czembor Smadar Ezrati Roberto Tuberosa 《Molecular breeding : new strategies in plant improvement》2010,26(2):189-228
Resistance to leaf rust (Puccinia triticina Eriks.) is a main objective for durum wheat (Triticum durum Desf.) breeding. Association mapping on germplasm collections is now being used as an additional approach for the discovery
and validation of major genes/QTLs. In this study, a collection of 164 elite durum wheat accessions suitable for association
mapping has been tested for leaf rust response at the seedling stage and under field conditions (adult plant stage). Seedling
tests were carried out with 25 selected isolates from durum wheat, bread wheat and triticale, while field experiments were
carried out in artificially inoculated plots in Italy and in Mexico. The collection has been profiled with 225 simple sequence
repeat (SSR) loci of known map position and a PCR assay targeting Ppd-A1. Associations showing highly consistent experiment-wise significances across leaf rust isolates and field trials were mainly
detected for the 7BL distal chromosome (chr.) region (harbouring Lr14 from cultivar Llareta INIA and QLr.ubo-7B.2 from cultivar Creso) and for two chr. regions located in chrs. 2A and 2B. Additionally, isolate-specific associations and/or
associations with smaller effects in the field trials were identified in most of the chromosomes. The chr. 7BL distal region
was investigated in detail through haplotyping with 15 SSR markers, revealing that the Creso and Llareta INIA alleles are
identical by descent at 6 adjacent SSR loci in the most distal 7BL region spanning 8 cM. Association mapping allowed us to
further refine the map location of the Lr14/QLr.ubo-7B.2 resistance gene to the most distal region of the linkage group, tagged by Xcfa2257.2, Xgwm344.2 and Xwmc10. The resistant haplotype is present in a number of accessions (ca. 15% of the accessions included in the collection) from
the Italian, CIMMYT and ICARDA breeding programmes. Therefore, this chr. 7BL region can be considered as the most important
source of resistance to leaf rust currently exploited by durum breeders in the Mediterranean areas. Furthermore, the field
trials at the adult plant stage allowed us to identify marker associations (e.g. chrs. 2BL and 3BS, proximal regions; chr.
7BS, distal region) which suggest the presence of minor QTLs for slow-rusting resistance. 相似文献
85.
Parental investment strategies can be fixed or flexible. A fixed strategy predicts making all offspring a single ‘optimal’
size. Dynamic models predict flexible strategies with more than one optimal size of offspring. Patterns in the distribution
of offspring sizes may thus reveal the investment strategy. Static strategies should produce normal distributions. Dynamic
strategies should often result in non-normal distributions. Furthermore, variance in morphological traits should be positively
correlated with the length of developmental time the traits are exposed to environmental influences. Finally, the type of
deviation from normality (i.e., skewed left or right, or platykurtic) should be correlated with the average offspring size.
To test the latter prediction, we used simulations to detect significant departures from normality and categorize distribution
types. Data from three species of ants strongly support the predicted patterns for dynamic parental investment. Offspring
size distributions are often significantly non-normal. Traits fixed earlier in development, such as head width, are less variable
than final body weight. The type of distribution observed correlates with mean female dry weight. The overall support for
a dynamic parental investment model has implications for life history theory. Predicted conflicts over parental effort, sex
investment ratios, and reproductive skew in cooperative breeders follow from assumptions of static parental investment strategies
and omnipresent resource limitations. By contrast, with flexible investment strategies such conflicts can be either absent
or maladaptive.
Electronic Supplementary Material Supplementary material is available for this article at 相似文献
86.
The chemistry of cell signaling by reactive oxygen and nitrogen species and 4-hydroxynonenal 总被引:2,自引:0,他引:2
Forman HJ Fukuto JM Miller T Zhang H Rinna A Levy S 《Archives of biochemistry and biophysics》2008,477(2):183-195
During the past several years, major advances have been made in understanding how reactive oxygen species (ROS) and nitrogen species (RNS) participate in signal transduction. Identification of the specific targets and the chemical reactions involved still remains to be resolved with many of the signaling pathways in which the involvement of reactive species has been determined. Our understanding is that ROS and RNS have second messenger roles. While cysteine residues in the thiolate (ionized) form found in several classes of signaling proteins can be specific targets for reaction with H2O2 and RNS, better understanding of the chemistry, particularly kinetics, suggests that for many signaling events in which ROS and RNS participate, enzymatic catalysis is more likely to be involved than non-enzymatic reaction. Due to increased interest in how oxidation products, particularly lipid peroxidation products, also are involved with signaling, a review of signaling by 4-hydroxy-2-nonenal (HNE) is included. This article focuses on the chemistry of signaling by ROS, RNS, and HNE and will describe reactions with selected target proteins as representatives of the mechanisms rather attempt to comprehensively review the many signaling pathways in which the reactive species are involved. 相似文献
87.
Golan G Shallom D Teplitsky A Zaide G Shulami S Baasov T Stojanoff V Thompson A Shoham Y Shoham G 《The Journal of biological chemistry》2004,279(4):3014-3024
Alpha-glucuronidases cleave the alpha-1,2-glycosidic bond between 4-O-methyl-d-glucuronic acid and short xylooligomers as part of the hemicellulose degradation system. To date, all of the alpha-glucuronidases are classified as family 67 glycosidases, which catalyze the hydrolysis via the investing mechanism. Here we describe several high resolution crystal structures of the alpha-glucuronidase (AguA) from Geobacillus stearothermophilus, in complex with its substrate and products. In the complex of AguA with the intact substrate, the 4-O-methyl-d-glucuronic acid sugar ring is distorted into a half-chair conformation, which is closer to the planar conformation required for the oxocarbenium ion-like transition state structure. In the active site, a water molecule is coordinated between two carboxylic acids, in an appropriate position to act as a nucleophile. From the structural data it is likely that two carboxylic acids, Asp(364) and Glu(392), activate together the nucleophilic water molecule. The loop carrying the catalytic general acid Glu(285) cannot be resolved in some of the structures but could be visualized in its "open" and "closed" (catalytic) conformations in other structures. The protonated state of Glu(285) is presumably stabilized by its proximity to the negative charge of the substrate, representing a new variation of substrate-assisted catalysis mechanism. 相似文献
88.
Shulami S Furdui C Adir N Shoham Y Anderson KS Baasov T 《The Journal of biological chemistry》2004,279(43):45110-45120
The enzyme 3-deoxy-d-manno-2-octulosonate-8-phosphate (KDO8P) synthase is metal-dependent in one class of organisms and metal-independent in another. We have used a rapid transient kinetic approach combined with site-directed mutagenesis to characterize the role of the metal ion as well as to explore the catalytic mechanisms of the two classes of enzymes. In the metal-dependent Aquifex pyrophilus KDO8P synthase, Cys11 was replaced by Asn (ApC11N), and in the metal-independent Escherichia coli KDO8P synthase a reciprocal mutation, Asn26 to Cys, was prepared (EcN26C). The ApC11N mutant retained about 10% of the wild-type maximal activity in the absence of metal ions. Addition of divalent metal ions did not affect the catalytic activity of the mutant enzyme and its catalytic efficiency (kcat/Km) was reduced by only approximately 12-fold, implying that the ApC11N KDO8P synthase mutant has become a bone fide metal-independent enzyme. The isolated EcN26C mutant had similar metal content and spectral properties as the metal-dependent wild-type A. pyrophilus KDO8P synthase. EDTA-treated EcN26C retained about 6% of the wild-type activity, and the addition of Mn2+ or Cd2+ stimulated its activity to approximately 30% of the wild-type maximal activity. This suggests that EcN26C KDO8P synthase mutant has properties similar to that of metal-dependent KDO8P synthases. The combined data indicate that the metal ion is not directly involved in the chemistry of the KDO8P synthase catalyzed reaction, but has an important structural role in metal-dependent enzymes in maintaining the correct orientation of the substrates and/or reaction intermediate(s) in the enzyme active site. 相似文献
89.
Ginzberg I Perl A Genser M Wininger S Nemas C Kapulnik Y 《Journal of plant physiology》2004,161(5):611-620
Biotin is an essential cofactor for a variety of carboxylase and decarboxylase reactions and is involved in diverse metabolic pathways of all organisms. In the present study we tested the hypothesis that controlling biotin availability by the expression of Streptomyces avidinii streptavidin, would impede plant development. Transient expression of streptavidin fused to plant signal peptide, bacterial signal peptide or both, in tomato (Lycopersicon esculentum cv. VF36) plants resulted in various levels of tissue impairment, exhibited as lesion development on 1-week-old tomato seedlings. The least toxic construct was introduced to tomato (stable transformation) under the constitutive CaMV 35S promoter, and lesions appeared on stems, flower morphologies were modified and numbers and sizes of fruits were altered. Furthermore, tissue-specific expression of the streptavidin, by means of the beta-phaseolin or TobRB7 promoters, resulted in localised effects, i.e., impaired seed formation or seedless fruits, respectively, with no alteration in the morphology of the other plant organs. External application of biotin on streptavidin-expressing tomato plants prevented the degeneration symptoms and facilitated normal plant development. It can be concluded that expression of streptavidin in the plant cell can lead to local and temporal deficiencies in biotin availability, impairing developmental processes while biotin application restores plant growth cycle. 相似文献
90.
Ronit Lavi Michael Sinyakov Amram Samuni Smadar Shatz Harry Friedmann Asher Shainberg 《Free radical research》2013,47(9):893-902
Low-energy visible light (LEVL) has previously been found to modulate various processes in different biological systems. One explanation for the stimulatory effect of LEVL is light-induced reactive oxygen species formation. In the present study, both sperm and skin cells were illuminated with LEVL and were found to generate singlet oxygen (1O2). The detection of 1O2 was performed using a trapping probe, 2,2,6,6-tetramethyl-4-piperidone, coupled with electron paramagnetic resonance spectroscopy. In addition, we have shown that, together with 1O2 generation, LEVL illumination increases the reductive capacity of the cells, which explains the difficulties encountered in 1O2 detection. The potential of visible light to change the cellular redox state may explain the recently observed biostimulative effects exerted by LEVL. 相似文献