共查询到20条相似文献,搜索用时 31 毫秒
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Guermant C. Brygier J. Baeyensvolant D. Nijs M. Vincentelli J. Paul C. Looze Y. 《Analytical biochemistry》1995,230(2)
A method is described that allows quantitative determination of polyethylene glycol (PEG) concentrations by spectrophotometric measurement of fluorescein dye absorbance after its partitioning into an aqueous two-phase system containing mPEG (Mr 5 kDa) in the upper phase and ammonium sulfate in the lower phase. The absorbance decrease of fluorescein in the lower phase is directly proportional to the mPEG concentration, with two proportionality constants equal to 4.42 × 105 and 2.84 × 105 M−1 cm−1 in the range of 0-0.4 and 0.4-1 μM, respectively. This experimental technique can be extended to PEGs of other molecular weights by means of calibration curves that give for each size of PEG the adequate proportionality constants. The results indicate that the quantitative determination is not affected by the presence of many substances such as proteins, reducing agents, and salts, at the usual concentrations. 相似文献
3.
Lintao Zeng Caiqin Qin Guanghui He Wei Wang Wei Li Dongsheng Xu 《Carbohydrate polymers》2008,74(2):279-282
Dietary chitosans with different molecular weight Mw and the degree of deacetylation DDA (high molecular weight chitosan HCS with Mw 7.60 × 105 and DDA 85.5%, middle molecular weight chitosan MCS with Mw 3.27 × 104 and DDA 85.2%, chito-oligomer COS with Mw 0.99 × 103 and DDA 85.7% and water-soluble chitosan WSC with Mw 3.91 × 104 and DDA 52.6%) were used at the 1.05% level to feed mice for 90 days. Afterwards no pathological symptoms, clinical signs or deaths were observed. The body weight of mice in chitosan group and control group showed no significant difference. Although HCS, COS and WSC had no significant effect on the level of Fe, Zn and Cu in the tested mice’s liver, spleen, heart and kidney, MCS significantly increased the level of Fe, Zn and Cu in liver. Therefore dietary ingestion of chitosan did not depress the level of Fe, Zn and Cu in mice. 相似文献
4.
Shinichi Kitamura Takashi Hirano Kenichi Takeo Mitsuru Mimura Kanji Kajiwara Bjrn T. Stokke Tsutomu Harada 《International journal of biological macromolecules》1994,16(6)
The conformation and dilute solution properties of (2→1)-β-d-fructan in aqueous solution were studied by gel permeation chromatography, low-angle laser light-scattering photometry, viscometry, small-angle X-ray scattering and electron microscopy. Fractions covering a broad range of weight-average molecular weights (Mw) from 1.49 × 104 to 5.29 × 106 were obtained from a native sample by ultrasonic degradation and fractional precipitation. For Mw < 4 × 104, the intrinsic viscosity [η] varies with Mw0.71, indicating that the fructan chain behaves as a random coil expanded by an excluded-volume effect in this molecular weight region. For Mw > 105, [η] exhibits an unusually weak dependence on Mw and finally becomes almost independent of molecular weight. This behaviour is interpreted in terms of a globular conformation of the high-molecular-weight fructan molecules. Small-angle X-ray-scattering measurements and electron microscopic observations support this interpretation of the values of [η] observed. 相似文献
5.
The rheological properties of solutions of gellan were examined at high concentrations where there is entanglement coupling between gellan chains. An ionic liquid 1-butyl-3-methylimidazolium chloride (BmimCl) was used as a solvent. Concentrated solutions of gellan in BmimCl were obtained by using a hot-molding technique. The concentration of gellan was varied from 1.9 × 102 to 4.8 × 102 kg m−3. The measurement temperature ranged from 50 to 100 °C. The master curve of the angular frequency dispersion of the storage modulus for the gellan solutions showed a rubbery plateau at high angular frequency. The molecular weight between entanglements (Me) for gellan was obtained from the plateau modulus. From the concentration dependence curve of Me, Me for gellan in the molten state was determined to be 2.3 × 103. 相似文献
6.
Galactomannans isolated from legume seed endosperms, including those of commercial interest, have been characterized by multidetection aqueous SEC. Galactomannans derived from seeds of the Faboideae subfamily had substantially higher Mw than those from Caesalpinioideae seeds (Mw,Fab = 2.4–3.1 × 106 g/mol, Mw,Caes. = 0.86–2.1 × 106 g/mol) and within the latter botanical subfamily, an apparent correlation between Mw and the degree of galactose substitution DG was found. The molar mass distributions were unimodal and differed primarily by a scale factor, with distributional widths narrower than a true Flory ‘most-probable distribution’; good fits to Schulz–Zimm model were obtained. Across subfamilies no differences were found in the exponents of [η]–M and Rv–M relationships (0.61 ± 0.02, 0.54 ± 0.01, respectively), the Flory chain stiffness ratio (C∞ = 20 ± 1 (BSF analysis)), or the persistence length (Lp = 5.5 ± 0.2 nm) obtained from SEC fraction data. However, it was found that prefactors in the [η]–M and Rv–M relationships as well as the unperturbed parameter KΘ decrease in proportion to DG and therefore chain density. Generalized relationships incorporating galactose-dependent prefactors were therefore developed to model SEC fraction data of native galactomannans ([η]GM = (1800 ± 200) × Mo−1.61 × M0.61±0.02, Rv,GM = 0.63 ± 0.05 × Mo−0.54 × M0.54±0.01) as well as lower-M fractions obtained by ultrasonication ([η]GM = (730 ± 100) × Mo−1.71 × Mw0.71±0.02, Rv,GM = 0.49 ± 0.05 × Mo−0.57 × Mw0.57±0.01, M ≈ 1 × 105-native). As a consequence of this dependence and the observed patterns in molar mass variation, [η] varies within a narrow range for galactomannans as a whole despite substantial Mw differences. 相似文献
7.
Prostaglandins (PGs) have been shown to cytoprotect various tissue types against the toxic effects of many chemicals. The mechanism of this protection is poorly understood, but the involvement of cAMP is often implied. Only one previous study examined nervous tissue and PG protection. The present study was designed to determine if PGE2 affords cytoprotection to a more specific nervous tissue (embryonic neural retina) from the toxicity of actinomycin C (AMC) using a trypan blue exclusion assay. The lowest concentration of PGE2 (2 × 10−5M) had no effect, but as the concentration increased (3 × 10−5M and 5 × 10−5M), PGE2 did afford protection against AMC in a dose dependent fashion. Theophylline treated cells were not protected, suggesting that cAMP may not be the primary mechanism of protection. 相似文献
8.
A rapid method was developed to determine the molecular weight (Mn) of β-limit dextrin and dextrans (Leuconostoc mesenteroides) using a reducing power approach. The Mn of the β-limit dextrin was also estimated from high performance liquid chromatography (HPLC). Chromatograms were pre-calibrated with the dextrans. The three dextrins had a Mn of 2.09, 2.40 and 2.63 × 105 using the reducing method and 4.80, 5.90 and 2.80 × 105 by HPLC. The method could be employed to estimate Mn of dextrins where chromatographic systems were not available. 相似文献
9.
Stanka Stoeva Rossen Rachev Severin Severov Wolfgang Voelter Nicolay Genov 《Comparative biochemistry and physiology. Part B, Biochemistry & molecular biology》1995,110(4):761-765
The hemocyanin of Rapana thomasiana grosse (marine snail, gastropod) is a glycoprotein with a carbohydrate content of 8.9% (w/w) and monosaccharide constituents xylose, fucose, 3-OOmethylgalactose, mannose, galactose, N-acetylgalactosamine and N-acetylglucosamine residues. The two structural subunits of this oxygen carrier, RHSS1 and RHSS2, are unevenly glycosylated. On subtracting the carbohydrate contribution from the Mr values of 250 and 450 kDa attributed to the two subunits, values of 2.18 × 105 daltons and 4.30 × 105 daltons were calculated for the polypeptide part of the “light” and “heavy” subunits, respectively. Comparison of the monosaccharide compositions of gastropodan hemocyanins revealed qualitative similarities, as well as relationships between the quantities, of the individual monosaccharides: Man 3MeGal > GlcNAc GalNAc and Fuc Xyl 相似文献
10.
Sandoval A Fraisl P Arias-Barrau E Dirusso CC Singer D Sealls W Black PN 《Archives of biochemistry and biophysics》2008,477(2):363-371
These studies defined the expression patterns of genes involved in fatty acid transport, activation and trafficking using quantitative PCR (qPCR) and established the kinetic constants of fatty acid transport in an effort to define whether vectorial acylation represents a common mechanism in different cell types (3T3-L1 fibroblasts and adipocytes, Caco-2 and HepG2 cells and three endothelial cell lines (b-END3, HAEC, and HMEC)). As expected, fatty acid transport protein (FATP)1 and long-chain acyl CoA synthetase (Acsl)1 were the predominant isoforms expressed in adipocytes consistent with their roles in the transport and activation of exogenous fatty acids destined for storage in the form of triglycerides. In cells involved in fatty acid processing including Caco-2 (intestinal-like) and HepG2 (liver-like), FATP2 was the predominant isoform. The patterns of Acsl expression were distinct between these two cell types with Acsl3 and Acsl5 being predominant in Caco-2 cells and Acsl4 in HepG2 cells. In the endothelial lines, FATP1 and FATP4 were the most highly expressed isoforms; the expression patterns for the different Acsl isoforms were highly variable between the different endothelial cell lines. The transport of the fluorescent long-chain fatty acid C1-BODIPY-C12 in 3T3-L1 fibroblasts and 3T3-L1 adipocytes followed typical Michaelis–Menten kinetics; the apparent efficiency (kcat/KT) of this process increases over 2-fold (2.1 × 106–4.5 × 106 s−1 M−1) upon adipocyte differentiation. The Vmax values for fatty acid transport in Caco-2 and HepG2 cells were essentially the same, yet the efficiency was 55% higher in Caco-2 cells (2.3 × 106 s−1 M−1 versus 1.5 × 106 s−1 M−1). The kinetic parameters for fatty acid transport in three endothelial cell types demonstrated they were the least efficient cell types for this process giving Vmax values that were nearly 4-fold lower than those defined form 3T3-L1 adipocytes, Caco-2 cells and HepG2 cells. The same cells had reduced efficiency for fatty acid transport (ranging from 0.82 × 106 s−1 M−1 to 1.35 × 106 s−1 M−1). 相似文献
11.
Molecular mass and antitumor activities of sulfated derivatives of α-glucan from Poria cocos mycelia 总被引:1,自引:0,他引:1
Yulu Lin Lina Zhang Li Chen Yong Jin Fanbo Zeng Jing Jin Bo Wan Peter C.K. Cheung 《International journal of biological macromolecules》2004,34(5):231-236
Two kinds of water-insoluble (1 → 3)-α-d-glucan samples, ab-PCM3-I and ac-PCM3-I, isolated from different Poria cocos mycelia were sulfated, to produce two series of water-soluble derivatives ab-PCM3-I-S1–S5 and ac-PCM3-I-S1–S5, respectively. The derivatives having different weight-average molecular mass (Mw) were produced by changing reaction temperature and time as well as molar ratios between chlorosulfonic acid and number of hydroxyl groups in the glucan. The degrees of substitution (DS) of the sulfated derivatives were analyzed by elemental analysis (EA) to be 0.39–0.67 for ab-PCM3-I-S and 0.73–0.96 for ac-PCM3-I-S, respectively. The Mw and the intrinsic viscosity ([η]) of the samples ab-PCM3-I-S and the ac-PCM3-I-S were measured by size exclusion chromatography combined with laser light scattering (SEC–LLS) and viscometry in phosphate buffer solution (PBS) at 37 °C. The results indicated that their Mw ranged from 2.0 to 11.3 × 104 for the samples ab-PCM3-I-S, and 4.7 to 40.0 × 104 for the samples ac-PCM3-I-S. Moreover, the antitumor activities of the sulfated derivatives ab-PCM3-I-S and ac-PCM3-I-S against Sarcoma 180 tumor cell tested both in vitro and in vivo are significantly higher than those of the native α-d-glucans. Therefore, a moderate range of molecular mass from 2.0 × 104 to 40.0 × 104, relatively high chain stiffness and good water solubility of the sulfated derivatives are beneficial to the enhancement of their antitumor activities. 相似文献
12.
In vitro effects of arsenic in human peripheral lymphocytes (HPL) at three different doses – 3.6×10−4, 1.4×10−3 and 0.72×10−3 μM for 24 h before harvesting on sister chromatid exchanges (SCE), Cell cycle proliferative index/replicative index (CCPI/RI), %M1, %M2 and %M3, population doubling time (PDT) and average generation time (AGT) were examined. Andrographis paniculata (commonly referred to as ‘kalmegh’) has been used for centuries in traditional Indian and Chinese herbal medicine as a safe, natural folk remedy for assorted health concerns. In the present study, kalmegh (0.01 μg/7 ml culture media) was used along with the highest dose of arsenic; the results showed that arsenic induced increase in these genotoxic endpoints were fairly diminished by kalmegh. In addition, mutagenic in vitro effect of ethyl methanesulphonate (EMS) was used as a positive control in this study. It is thus concluded from this study that Andrographis has a protective role in arsenic toxicity. 相似文献
13.
The concentrations of PGE, PGF, and 6-keto-PGF1α were increased in rat seminal vesicle tissue following mating activity. Likewise, synthesis of PGE and PGF was stimulated by epinephrine (3 × 10−7to 3 × 10−6 M) in tissues and media from
incubations of intact rat seminal vesicles. The
stimulation was inhibited by phentolamine, an α-adrenoreceptor blocking agent. Carbamylcholine (2 × 10−6 M) and bradykinin (1 × 10−6 M) had no effect on PGE or PGF synthesis, even though both compounds stimulated contractility of the rat seminal vesicle at these concentrations. These data suggest that mating and adrenergic stimulation increase prostaglandin synthesis in] the rat seminal vesicle, probably through an α-adrenergically mediated mechanism. 相似文献
14.
Alexis Aspe Alejandra Orrego Emilio Alarcn Camilo Lpez-Alarcn Horacio Poblete Danilo Gonzlez-Nilo 《Bioorganic & medicinal chemistry letters》2009,19(22):291-6385
A new strategy to evaluate accessibility of antioxidants to radical proteins has been developed using nitroxide prefluorescent probes anchored into human serum albumin (HSA). Binding association constants for the nitroxide probes C343T and QT with HSA were 5 × 104 and 9 × 104 M−1, respectively. Rate constants for the nitroxide reduction by antioxidants in HSA were determined finding kHSA/kbuffer ratio of 0.8, 1.9, and 0.075 for ascorbic acid, Trolox, and caffeic acid, respectively, for the nitroxide C343T reduction. 相似文献
15.
An influence of methane concentration on the methanotrophic activity of a model landfill cover 总被引:3,自引:0,他引:3
Evaluation of kinetic parameters of methane oxidation under various conditions, on the basis of an analysis of the literature and the authors’ own laboratory research, is presented. Variation in methanotrophic activity in the profile of a simulated landfill cover was observed. The greatest activity was found at a depth of 60 cm. A low affinity (1/KM) and high potential activity (Vmax) were observed. Vmax values ranged from 0.11 × 10−3 to 0.86 × 10−3 units. The values of KM ranged from 0.6 to 2.9% of CH4 (v/v). 相似文献
16.
The molecular mass and size of five water-soluble polysaccharides isolated from Rhizoma Panacis Japonici (RPJ) were determined with laser light scattering (LLS), size-exclusion chromatography (SEC) combined with LLS (SEC–LLS), dynamic light scattering (DLS), as well as transmission electron microscope (TEM). Their weight-average molecular masses (Mw) were 3.5 × 104, 1.47 × 105, 1.24 × 106, 9.26 × 105 and 1.36 × 106, radii of gyration (<s2>z1/2) were 14.7, 31.7, 50.8, 41.8 and 40.4 nm, and hydrodynamic radii (Rh) were 19.9, 37.5, 66.2, 52.1, and 55.2 nm, respectively. The results showed that molecular masses and sizes of the polysaccharides were influenced by the pH and temperature of the extraction mediums. The conformation parameters were calculated from the above data according to polymer solution theory. The values of ρ (= <s2>z1/2/Rh) were from 0.7 to 0.8, exponents (ν) of <s2>z1/2 = k Mwν were from 0.31 to 0.43, and fractal dimension (df) were from 2.3 to 3.2, respectively. The results revealed that all of the polysaccharides existed as spheres in 0.15 M NaCl aqueous solution. TEM and atomic force microscope (AFM) further confirmed the spherical morphologies of these molecules. The spherical conformations of the polysaccharides were a result of their highly branched structures. 相似文献
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18.
Toshiaki Mori Momoko Toyoda Tatsuro Ohtsuka Yoshio Okahata 《Analytical biochemistry》2009,395(2):211-216
A biotinylated mannotriose (Man3-bio) was dispersively immobilized in the matrix of biotinylated lactose (Gal-Glc-bio) on a streptavidin-covered, 27-MHz quartz crystal microbalance (QCM), and binding kinetics of concanavalin A (Con A) to Man3-bio in the Gal-Glc-bio matrix could be obtained from frequency decreases (mass increases) of the QCM. Association constants (Ka) and binding and dissociation rate constants (kon and koff) could be determined separately as the 1:1 and 1:2 bindings of Con A to Man3-bio on the surface. When Man3-bio was immobilized with content of 1 to 5 mol% in the matrix, the 1:1 binding of Con A to Man3-bio was obtained as Ka = (4 ± 1) × 106 M−1, kon = (4 ± 1) × 104 M−1 s−1, and koff = (12 ± 2) × 10–3 s−1. On the contrary, when Man3-bio was immobilized with content of 20 to 100 mol% in the matrix, the 1:2 binding of Con A to Man3-bio was obtained as Ka = (14 ± 2) × 106 M−1, kon = (14 ± 2) × 104 M−1 s−1, and koff = (7 ± 2) × 10–3 s−1. Thus, Ka for the 1:2 binding was 10 times larger than that for the 1:1 binding, with a three times larger binding rate constant (kon) and a three times smaller dissociation rate constant (koff). This is the first example to obtain separate kinetic parameters for the 1:1 and 1:2 bindings of lectins to carbohydrates on the surface. 相似文献
19.
Plasmids were isolated from two species ofStreptosporangium by CsCl-ethidium bromide equilibrium density gradient centrifugation. A plasmid isolated fromS. brasiliense, designated pSgB-1, was characterized by electron microscopy and agarose gel electrophoresis. The pSgB-1 plasmid is a closed circular DNA molecule of 9.4 × 106 Da. A restriction endonuclease map was generated and unique cleavage sites were found forEcoRI, ClaI, XbaI, and MstII. Another plasmid, pSgV-1, isolated fromS. viriodogriseum, has an estimatedMr of 54 × 106. The pSgB-1 plasmid is phenotypically cryptic but an unusual phenotypic trait, resembling phage plaques, may be associated with theS. viridogriseum plasmid pSgV-1. 相似文献
20.
Susan A. Moore 《Experimental cell research》1987,171(2)
A highly sensitive, kinetically unambiguous assay for α-factor-induced delay of cell passage through the “start” step of cell division in yeast is presented. The assay employs perfusion with periodic microscopy to monitor the bud emergence kinetics on the 20% of cells within an exponentially growing population which exist prior to the α-factor execution point of start. The t1/2 for cell passage through start by this population of cells is 31 min in the absence of α-factor. The inhibition constant, KI, represents the α-factor concentration which produces a 50% inhibition of this rate and is equal to 2×10−10M. A second assay for maximal cell division arrest by α-factor on whole populations of cells is presented. This assay shows a maximum cell division arrest time of 125±5 h at saturating α-factor, and a K50 (that is, an α-factor concentration which produces a half-maximal response) of 2.5×10−8M. Both assays were performed in the effective absence of α-factor inactivation. Values of the dissociation constant KD and total number of receptors per cell which specifically mediate cell division arrest or delay were estimated to be 2.5×10−8M and 104, respectively. These estimates, along with the quantitative dose-response data for division arrest which are presented here, are consistent with each receptor·α-factor complex which is present on the cell at equilibrium producing a 43±10 s delay of cell passage through start. Surprisingly, this number is constant within twofold over the entire range of cellular division arrest responses to α-factor, that is, from a 1.9-fold inhibition of the rate of cell passage through start at 0.17 nM α-factor to a 125±5 h maximum arrest at saturating α-factor concentrations of >170 nM. The possible significance of this observation toward the mechanism of α-factor-induced cell division arrest is discussed. 相似文献