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991.
Polysaccharides excreted by cowpea Rhizobium strains JLn(c) and RA-1 were mixtures of complex acidic exopolysaccharides and low molecular weight neutral glucans. These polymers were fractionated using gel filtration chromatography. Purified fractions of the acidic heteropolymer reacted with peanut agglutinin to give precipitin bands when subjected to Ouchterlony gel diffusion. The acidic exopolysaccharide was found to contain mainly glucose, galactose, glucuronic acid, mannose and fucose. The non-carbohydrate substituents of the acidic heteropolymer were pyruvate, acetate and uronate which were identified by infrared and proton nuclear magnetic resonance spectroscopy as well as by chemical analysis.Abbreviations EPS
Extracellular polysaccharide
- YEM
yeast extract mannitol
- PNA
peanut agglutination
-
1H-NMR
proton nuclear magnetic resonance 相似文献
992.
Viktor Hornak Markus Eilers Mordechai Sheves Steven O. Smith 《Journal of molecular biology》2010,396(3):510-527
Structural restraints provided by solid-state NMR measurements of the metarhodopsin II intermediate are combined with molecular dynamics simulations to help visualize structural changes in the light activation of rhodopsin. Since the timescale for the formation of the metarhodopsin II intermediate (> 1 ms) is beyond that readily accessible by molecular dynamics, we use NMR distance restraints derived from 13C dipolar recoupling measurements to guide the simulations. The simulations yield a working model for how photoisomerization of the 11-cis retinylidene chromophore bound within the interior of rhodopsin is coupled to transmembrane helix motion and receptor activation. The mechanism of activation that emerges is that multiple switches on the extracellular (or intradiscal) side of rhodopsin trigger structural changes that converge to disrupt the ionic lock between helices H3 and H6 on the intracellular side of the receptor. 相似文献
993.
Lehmann M Dettling M Brunner H Tovar GE 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2004,808(1):43-50
The binding of L-Boc-phenylalanine anilide (BFA) and L-Boc-phenylalanine (phe) to molecularly imprinted and non-imprinted polymer nanoparticles consisting of poly[(ethylene glycol dimethacrylate)-co-(methacrylic acid)] has been investigated by adsorption experiments and mathematical modeling. The experimental isotherms have been mathematically adapted following the models of Freundlich, Langmuir, Langmuir-Freundlich, Bi-Langmuir, and extended Langmuir. The extended Langmuir model differentiated between specific and nonspecific binding of the ligand to the receptor nanoparticles and rendered excellent fitting of the experimental data. It delivered a thermodynamic and kinetic parameter set on the experimental association curves of L-BFA by L-BFA-imprinted nanospheres in suspension experiments with the equilibrium constant KD= 4.09 +/- 0.69 micromol L(-1) and the kinetic association rate constant Ka= 5.60 mL micromol(-1) min(-1). 相似文献
994.
Th. Bittner J. Voigt G. Kehrberg H. -J. Eckert G. Renger 《Photosynthesis research》1991,28(3):131-139
Utilizing a two-beam technique in the frequency domain, the pumped absorption of PS II membrane fragments from spinach and of acetonic chlorophyll-a solutions was measured at room temperature. In a very narrow wavelength region (0.2 nm around the pump pulse wavelength) the relative test beam transmission exhibited either a decrease or an increase, respectively, dependent on the intensity of a strong pump beam. In contrast, the transmission changes of chl-a solutions were not affected by the wavelength mistuning between pump and test beam. The data obtained for PS II membrane fragments were interpreted in terms of excited state absorption of pigment-protein clusters within the light-harvesting complex of PS II. The interpretation of the small absorption band as a homogeneously broadened line led to a transversal relaxation time for chlorophyll in vivo of about 1 ps.Abbreviations PS I
photosystem I of green plants
- PS II
photosystem II of green plants
- P700
primary donor of PS I
- P680
primary donor of PS II 相似文献
995.
Reconstruction of historical productivity using visible-near-infrared (VNIR) reflectance properties from boreal and saline lake sediments 总被引:2,自引:0,他引:2
Biplob Das 《Aquatic Ecology》2007,41(2):209-220
Chlorophylls preserved in lake sediments have been used as a proxy to infer past trophic status. Recently, it has been demonstrated
that visible-near-infrared (VNIR) reflectance spectroscopy can provide a rapid and non-destructive estimation of fossil chlorophylls
from alpine lake sediments. The present study explores, (a) the applicability of VNIR reflectance spectroscopy to reconstructing
historical productivity from boreal and saline lakes, and (b) the ability of an inference model combining all lake types to
reconstruct historical chlorophyll concentrations from lake sediments. Results revealed that regardless of the lake type,
a common sediment spectral feature of a reflectance trough centered near 675 nm, was observed. Additionally, the amplitude
of reflectance in the VNIR region differs within and among lakes depending on their trophic states. The inferred concentration
of total chlorophylls and derivatives from sediment spectral properties reflected a recent nutrient enrichment in most of
the study lakes. Predicted chlorophyll concentration, when plotted against high-pressure liquid chromatography (HPLC) measured
concentration combining all lake types, was found to be statically significant (r
2 = 0.80, P < 0.01). Collectively, results from this study indicate that regardless of the lake type, a common chlorophyll absorption
feature near 675 nm can be detected, which is associated with contrasting limnological settings and, therefore, can be used
as a viable tool to reconstruct paleoproductivity. A similar approach can be implemented for rapid and non-destructive detection
of historical lake water quality in a wide range of lake sediments. 相似文献
996.
Guangshun Wang 《生物化学与生物物理学报:生物膜》2010,1798(2):114-12455
Worldwide bacterial resistance to traditional antibiotics has drawn much research attention to naturally occurring antimicrobial peptides (AMPs) owing to their potential as alternative antimicrobials. Structural studies of AMPs are essential for an in-depth understanding of their activity, mechanism of action, and in guiding peptide design. Two-dimensional solution proton NMR spectroscopy has been the major tool. In this article, we describe the applications of natural abundance 13C NMR spectroscopy that provides complementary information to 2D 1H NMR. The correlation of 13Cα secondary shifts with both 3D structure and heteronuclear 15N NOE values indicates that natural abundance carbon chemical shifts are useful probes for backbone structure and dynamics of membrane peptides. Using human LL-37-derived peptides (GF-17, KR-12, and RI-10), as well as amphibian antimicrobial and anticancer peptide aurein 1.2 and its analog LLAA, as models, we show that the cross peak intensity plots of 2D 1H-13Cα HSQC spectra versus residue number present a wave-like pattern (HSQC wave) where key hydrophobic residues of micelle-bound peptides are located in the troughs with weaker intensities, probably due to fast exchange between the free and bound forms. In all the cases, the identification of aromatic phenylalanines as a key membrane-binding residue is consistent with previous intermolecular Phe-lipid NOE observations. Furthermore, mutation of one of the key hydrophobic residues of KR-12 to Ala significantly reduced the antibacterial activity of the peptide mutants. These results illustrate that natural abundance heteronuclear-correlated NMR spectroscopy can be utilized to probe backbone structure and dynamics, and perhaps to map key membrane-binding residues of peptides in complex with micelles. 1H-13Cα HSQC wave, along with other NMR waves such as dipolar wave and chemical shift wave, offers novel insights into peptide-membrane interactions from different angles. 相似文献
997.
998.
槭乳菇Lactarius acerrimus,乳菇中仅有的具有双孢担子的物种,曾经在中国被多次报道。我们在研究了该种的馆藏凭证标本后并未证实它在中国的分布,而是在中国发现了它的近缘种李玉乳菇L. liyuanus (新种)。李玉乳菇的典型特征为:菌盖黄褐色具环纹、边缘具短毛,菌柄具窝斑,乳汁白色、不变色、具辣味,孢子具尖而高的条脊。它的担子为4孢,孢子较小具高而尖的条脊,这两点与槭乳菇明显不同。文中提供了该种的条形码ITS序列、其他多基因序列和详细的形态描述,同时给出了对国内馆藏槭乳菇标本的重新鉴定结果。 相似文献
999.
Svetlana V. Shilova Grigory M. Mirgaleev Ksenia A. Romanova Yury G. Galyametdinov 《Biopolymers》2023,114(10):e23555
This work reports synthesis of pH-responsive alginate/chitosan hydrogel spheres with the average diameter of 2.0 ± 0.05 mm, which contain cefotaxime that is an antibiotic of the cefalosporine group. The spheres provided the cefotaxime encapsulation efficiency of 95 ± 1%. An in vitro release of cefotaxime from the spheres in the media that simulate human biological fluids in peroral delivery conditions was found to be a pH-dependent process. The analysis of cefotaxime release kinetics by the Korsmeyer–Peppas model revealed a non-Fickian mechanism of its diffusion, which may be related to intermolecular interactions occurring between the antibiotic and chitosan. Conductometry, UV spectroscopy, and IR spectroscopy were used to study complexation of chitosan with cefotaxime in aqueous media with varied pH, characterize the composition of the complexes, and calculate their stability constants. The composition of the cefotaxime–chitosan complexes was found to correspond to the 1.0:4.0 and 1.0:2.0 molar ratios of the components at pH 2.0 and 5.6, respectively. Quantum chemical modeling was used to evaluate energy characteristics of chitosan–cefotaxime complexation considering the influence of a solvent. 相似文献
1000.
Enhancement of maternal recognition of pregnancy with parthenogenetic embryos in bovine embryo transfer 总被引:1,自引:0,他引:1
Hiroki Hirayama Satoru Moriyasu Soichi Kageyama Ken Sawai Hitomi Takahashi Masaya Geshi Takashi Fujii Takeshi Koyama Keisuke Koyama Akio Miyamoto Motozumi Matsui Akira Minamihashi 《Theriogenology》2014
This study was performed to elucidate the changes in IFNT messenger RNA (mRNA) levels in in vivo–fertilized and parthenogenetic bovine embryos and their interferon-τ (IFNT) secretion amounts during the elongation phase. We assessed the induction capability of maternal recognition of pregnancy by parthenogenetic embryos and attempted cotransfer of in vivo–fertilized and parthenogenetic embryos. The expression level of IFNT mRNA in in vivo–fertilized embryos peaked on Day 18 after estrus, and the highest amount of uterine IFNT was observed on Day 20. Transfer of 10 parthenogenetic embryos produced a detectable amount of uterine IFNT. Transfer of one or three parthenogenetic embryos inhibited luteolysis. An increase in ISG15 mRNA levels in peripheral granulocytes was induced by the transfer of three parthenogenetic embryos. Cotransfer of three parthenogenetic embryos significantly improved the pregnancy rate on Day 40 in code 3 in vivo–fertilized embryos compared with single transfer without parthenogenetic embryos (65% vs. 35%). However, the pregnancy rate on Day 90 (35%) in cotransfer of code 3 in vivo–fertilized embryos did not differ from that upon single transfer (29%), because the cotransfer group had a higher incidence of pregnancy loss than with single transfer (47% vs. 17%) after Day 40. Cotransfer did not affect the pregnancy rate of code 2 in vivo–fertilized embryos. The incidence of pregnancy loss was higher in cotransfer of code 2 in vivo–fertilized embryos than in single transfer (30% vs. 7%). In conclusion, parthenogenetic embryos in the elongation phase secreted IFNT, enabling induction of maternal recognition of pregnancy. The present study revealed that enhancement of the maternal recognition of pregnancy using parthenogenetic embryos promoted the viability of poor-quality embryos until Day 40 of gestation. However, the incidence of pregnancy loss increased after Day 40 in the cotransfer of parthenogenetic embryos. A technique for promoting the full-term survival of poor-quality embryos is needed. 相似文献