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1.
The anation reaction of aquopentaamminecobalt(III) by acetate has been studied in the temperature range 60–80°C and acidity range 1.0 ≦ pH ≦ 5.5 for total acetate concentrations ≦ 0.5 M and at ionic strength 1.0 M. The anation by acetic acid follows second-order kinetics (k0), whereas the kinetic results for the anation by acetate (Q1, k1) provide evidence for the formation of an ion-pair with the complex ion. Typical experimental results at 70°C are k0 = 5.33 X 10−5 M−1 sec−1, Q1 = 5.87 M−1 and k1 = 1.46 X 10−4sec−1. The activation parameters for the different reaction paths are reported and the results discussed with reference to various other anation reactions of Co(III) complexes. 相似文献
2.
Consider testing the hypothesis of no treatment effects against a postulated ranking of the m treatments, given data from n Complete Blocks. A suitable test statistic is the weighted average rank correlation w = σbQiCi where Ci is the correlation between the postulated ranking and the ranking observed within the ith block, Qi is the rank of the ith block with respect to credibility, and the bi's are weights such that 0 ≦ b1 ≦ … ≦ bn. In this paper we introduce some simple statistics: the first extends the signed-rank statistic to m ≦ 3, the second uses a simple measure of correlation based on the antirank, and the third a statistic based on Spearman's footrule. Tables for critical values are provided and the normal approximation is investigated. 相似文献
3.
G. Mirzaghaderi G. Karimzadeh H. S. Hassani M. Jalali-Javaran A. Baghizadeh 《Biologia Plantarum》2010,54(2):252-258
The new salt tolerant cereal, Tritipyrum (2n=6x=42, AABBEbEb) offers potential to introduce desirable characters for wheat improvements. This study was aimed to generate a segregating
population from Iranian local wheat cultivars (2n=6x=42, AABBDD) and Tritipyrum crosses, study of the meiotic behaviour in F2 hybrids and identification of Eb chromosomes in F3 individuals. Results showed meiotic abnormalities in F2 plants and different pairing frequency in the meiosis among F2 plants. Genomic in situ hybridization revealed that total and Eb chromosome number of F3 seeds ranged from 39 to 45 and 0 to 10, respectively. A significant prevalence of hyper-aneuploidy was observed among F3 genotypes. C-banding patterns identified Eb chromosomes in Tritipyrum, indicating that it also can be useful to study wheat-Tritipyrum derivatives. 相似文献
4.
Discs of cortical and perimedullary tissue from tubers of potato (Solanum tuberosum L. cv. Superior) formed adventitious shoots when cultured on a medium containing Murashige and Skoog's salts, myo-inositol, 100 mg/l; folic acid, 0.5 mg/l; D-biotin, 0.05 mg/l; gibberellic acid (GA3), 0.5 mg/l; thiamine ˙ HCl, 0.1 mg/l; glycine, 2.0 mg/l; pyridoxine ˙ HCl, 0.5 mg/l; nicotinic acid, 0.5 mg/l; sucrose, 25 g/l; casein hydrolysate, 1 g/l; Bacto agar, 9.0 g/l; and a cytokinin [N6-benzylaminopurine (BAP), N6-γ,γ-dimethylallylaminopurine (2iP), or N6-furfurylaminopurine (kinetin)]. Discs of pith tissue either failed to survive or produced callus but did not undergo morphogenesis. Cytokinin was essential for explant survival, while BAP at 3.0 mg/l was most efficacious in promoting shoot initiation. Auxin was not essential for shoot initiation or development; however, a low concentration (0.03 mg/l) of α-naphthaleneacetic acid (NAA) stimulated both explant survival and the number of shoots produced per disc. Indole-3-butyric acid (IBA) and indole-3-acetic acid (IAA) did not stimulate shoot initiation. GA3 was essential for both shoot initiation and subsequent shoot development. The highest incidence of morphogenesis (over 100 shoots in 12 weeks) occurred from tuber discs cultured at 18°C constant and under a photon flux density of 60 μE m-2s-1. No difference in regenerative ability was found in explants taken from source tubers stored for 0 to 20 weeks at 4°C. A histological examination indicated that shoots developed from small clusters of meristematic cells which were initiated from within small protuberances on the surface of the tuber disc 3 weeks after transfer. 相似文献
5.
The temperature-profile curve of ethanol production of the yeast Saccharomyces cerevisiae Sc 5 is shown. Accordingly the biokinetic sphere of ethanol formation consists of 5 ranges. The maximum specific ethanol formation rate v0 is reached within the temperature limits of 32°C ≦ T ≦ 36°C, and the maximum temperature for ethanol formation amounts to T″max = 57°C. Within the first suboptimum temperature range ethanol formation is not retarded thermally. Using a modified ARRHENIUS equation the activation energy of ethanol formation was calculated to be ΔHÊtOH = (78.5 ± 2.2) kJ/mol. 相似文献
6.
Abstract Tomato plants (Lycopersicon esculentum Mill. cv. San Marzano), grown in dilute nutrient solutions containing (in meq ˙ 1-1) 0.5 NaNO3, 0.5 NH4NO3 or 0.25 (NH4)2 SO4 as the nitrogen source, were detopped for collection of xylem sap and measurement of trans-root electrical potentials. The plant parts and the xylem exudate were subsequently analysed for mineral content. The commonly observed effects of NH4+ were noted, including reduction of calcium concentration in the xylem sap, and of calcium content in stems and leaves, compared with NO3-fed plants. This effect was attributed principally to the less negative trans-root electrical potential measured in NH4+-fed plants, and the resultant reduction of inward driving force on passively moving divalent cations. 相似文献
7.
Christopher M. Bianchetti George C. Blouin Eduard Bitto John S. Olson George N. Phillips Jr. 《Proteins》2010,78(4):917-931
The protein from Arabidopsis thaliana gene locus At1g79260.1 is comprised of 166‐residues and is of previously unknown function. Initial structural studies by the Center for Eukaryotic Structural Genomics (CESG) suggested that this protein might bind heme, and consequently, the crystal structures of apo and heme‐bound forms were solved to near atomic resolution of 1.32 Å and 1.36 Å, respectively. The rate of hemin loss from the protein was measured to be 3.6 × 10?5 s?1, demonstrating that it binds heme specifically and with high affinity. The protein forms a compact 10‐stranded β‐barrel that is structurally similar to the lipocalins and fatty acid binding proteins (FABPs). One group of lipocalins, the nitrophorins (NP), are heme proteins involved in nitric oxide (NO) transport and show both sequence and structural similarity to the protein from At1g79260.1 and two human homologues, all of which contain a proximal histidine capable of coordinating a heme iron. Rapid‐mixing and laser photolysis techniques were used to determine the rate constants for carbon monoxide (CO) binding to the ferrous form of the protein (k′CO = 0.23 μM?1 s?1, kCO = 0.050 s?1) and NO binding to the ferric form (k′NO = 1.2 μM–1 s–1, kNO = 73 s?1). Based on both structural and functional similarity to the nitrophorins, we have named the protein nitrobindin and hypothesized that it plays a role in NO transport. However, one of the two human homologs of nitrobindin contains a THAP domain, implying a possible role in apoptosis. Proteins 2010. © 2009 Wiley‐Liss, Inc. 相似文献
8.
Melissa R. Miller Weiming Zhang Scott P. Sibbel Carl D. Langefeld Donald W. Bowden Steven M. Haffner Richard N. Bergman Jill M. Norris Tasha E. Fingerlin 《Obesity (Silver Spring, Md.)》2010,18(3):555-562
The IKKβ/NF‐κB pathway is known to play an important role in inflammatory response and has also recently been implicated in the process of insulin resistance. We hypothesized that one or more variants in the IκBα gene (NFKBIA) or surrounding untranslated regions would be associated with insulin sensitivity (SI) in Hispanic‐American families. We tested for association between 25 single‐nucleotide polymorphisms (SNPs) in and near NFKBIA and SI in 981 individuals in 90 Hispanic‐American families from the Insulin Resistance Atherosclerosis (IRAS) Family Study. SNP rs1951276 in the 3′ flanking region of NFKBIA was associated with SI in the San Antonio (SA) sample after adjusting for age, gender, and admixture (uncorrected P = 1.69 × 10?5; conservative Bonferroni correction P = 3.38 × 10?4). Subjects with at least one A allele for NFKBIA rs1951276 had ~29% lower SI compared to individuals homozygous for the G allele in the SA sample. Although not statistically significant, the effect was in the same direction in the San Luis Valley (SLV) sample alone (P = 0.348) and was significant in the combined SA and SLV samples (P = 5.37 × 10?4; presence of A allele associated with ~20% lower SI). In SA, when adjusted for subcutaneous adipose tissue area (SAT, cm2), the association was modestly attenuated (P = 1.25 × 10?3), but the association remained highly significant after adjustment for visceral adipose tissue area (VAT, cm2; P = 4.41 × 10?6). These results provide corroborating evidence that the NF‐κB/IKKβ pathway may mediate obesity‐induced insulin resistance in humans. 相似文献
9.
Agneta L. Sunehag Chiara Dalla Man Gianna Toffolo Morey W. Haymond Dennis M. Bier Claudio Cobelli 《Obesity (Silver Spring, Md.)》2009,17(2):233-239
Given the increase in the incidence of insulin resistance, obesity, and type 2 diabetes in children and adolescents, it would be of paramount importance to assess quantitative indices of insulin secretion and action during a physiological perturbation, such as a meal or an oral glucose‐tolerance test (OGTT). A minimal model method is proposed to measure quantitative indices of insulin secretion and action in adolescents from an oral test. A 7 h, 21‐sample OGTT was performed in 11 adolescents. The C‐peptide minimal model was identified on C‐peptide and glucose data to quantify indices of β‐cell function: static φs and dynamic φd responsivity to glucose from which total responsivity φ was also measured. The glucose minimal model was identified on glucose and insulin data to estimate insulin sensitivity, SI, which was compared to a reference measure, SIref, provided by a tracer method. Disposition indices, which adjust insulin secretion for insulin action, were then calculated. Indices of β‐cell function were φs = 51.35 ± 8.89 × 10?9min?1, φd = 1,392 ± 258 × 10?9, and φ = 82.09 ± 17.70 × 10?9min?1. Insulin sensitivity was SI = 14.19 ± 2.73 × 10?4, not significantly different from SIref = 14.96 ± 3.04 × 10?4 dl/kg·min per µU/ml, and well correlated: r = 0.98, P < 0.0001, thus indicating that SI can be accurately measured from an oral test. Disposition indices were DIs = 1,040 ± 201 × 10?14 dl/kg/min2 per pmol/l, DId = 33,178 ± 10,720 × 10?14 dl/kg/min per pmol/l, DI = 1,844 ± 522 × 10?14 dl/kg/min2 per pmol/l. Virtually the same minimal model assessment was obtained with a reduced 3 h, 9‐sample protocol. OGTT interpreted with C‐peptide and glucose minimal model has the potential to provide novel insight regarding the regulation of glucose metabolism in adolescents, and to evaluate the effect of obesity and interventions such as diet and exercise. 相似文献
10.
We present a new soil respiration model, describe a formal model testing procedure, and compare our model with five alternative models using an extensive data set of observed soil respiration. Gas flux data from rangeland soils that included a large number of measurements at low temperatures were used to model soil CO2 emissions as a function of soil temperature and water content. Our arctangent temperature function predicts that Q10 values vary inversely with temperature and that CO2 fluxes are significant below 0 °C. Independent data representing a broad range of ecosystems and temperature values were used for model testing. The effects of plant phenology, differences in substrate availability among sites, and water limitation were accounted for so that the temperature equations could be fairly evaluated. Four of the six tested models did equally well at simulating the observed soil CO2 respiration rates. However, the arctangent variable Q10 model agreed closely with observed Q10 values over a wide range of temperatures (r2 = 0.94) and was superior to published variable Q10 equations using the Akaike information criterion (AIC). The arctangent temperature equation explained 16–85% of the observed intra-site variability in CO2 flux rates. Including a water stress factor yielded a stronger correlation than temperature alone only in the dryland soils. The observed change in Q10 with increasing temperature was the same for data sets that included only heterotrophic respiration and data sets that included both heterotrophic and autotrophic respiration. 相似文献
11.
The production costs of ethanol are dependent on the efficiency of the substrate-ethanol conversion to a high degree. The more the substrate used during the fermentation is converted into alcohol the better is the economy of the process. Therefore the ethanol yield Y SP is an important object of the process optimization. In batch fermentation processes the most essential influence factors are the initial biomass concentration X0, the initial substrate concentration S0, the temperature T, and the pH-value. A model reflecting the complex relationships between these influence factors and the ethanol yield could be obtained by regression. It allows an exact valuation of these optimum process parameters which are necessary for realizing high ethanol yields in the batch fermentation. For the strain Saccharomyces cerevisiae Sc 5 used in this research was found an ethanol yield maximum YSP = 0˙5384 at the parameters X0 = 64.61 g/l S0 = 82.91 g/l T = 36.45°C pH = 6.54. 相似文献
12.
Fernando Martínez-Jerónimo Jesús Rodríguez-Estrada Rafael Villaseñor-Córdova 《Hydrobiologia》2007,594(1):69-73
Moina micrura is a cosmopolitan, cyclic parthenogenetic, cladoceran with ample morphological and ecological plasticity that inhabits temperate,
tropical, and subtropical regions of the world. Sexual reproduction in cladocerans is a phenomenon induced by environmental
factors, mainly associated with adverse conditions, including crowding. In this study we have assessed the effects of population
density combined with the volume available for individual development, on the number of newborns and on the sex ratio in the
progeny. Three parthenogenetic female densities (D
1 = 33 ind l−1, D
2 = 66 ind l−1, D
3 = 100 ind l−1) were assayed in combination with three culture volumes (V
1 = 30 ml, V
2 = 60 ml, V
3 = 120 ml), at 21°C. Once the reproduction began, progeny was isolated daily and counted, identifying female and male neonates.
Culture volume was the only factor that had a significant effect on the total progeny, as well as on the number of males in
the progeny; the highest sex ratio was recorded in D
2
V
1 (0.58), whereas the lowest was for D
1
V
3 (0.06). Female density had no significant effect on the number of sexual M. micrura. We hypothesize that male production (quantity and frequency) was higher in the lowest tested volume because of a reduction
in the space available per individual, but not necessarily associated with the physical interaction related with a high encounter
rate in more crowded conditions.
Guest editor: Piet Spaak
Cladocera: Proceedings of the 7th International Symposium on Cladocera 相似文献
13.
L. A. Pershina E. P. Devyatkina L. I. Belova N. V. Trubacheeva V. S. Arbuzova L. A. Kravtsova 《Russian Journal of Genetics》2009,45(10):1223-1229
Two alloplasmic wheat-barley substitution lines were studied: a line replaced at three pairs of chromosomes 1H
mar
(1B), 5H
mar
(5D), and 7H
mar
(7D), and the disomic-substituted line 7H
mar
(7D). The lines were constructed on the basis of individual plants from BC1F8 and BC2F6 progeny of barley-wheat hybrids (H. marinum subsp. gussoneanum Hudson (= H. geniculatum All.) (2n = 28) × T. aestivum L.) (2n = 42) (Pyrotrix 28), respectively. Moreover, the alloplasmic wheat-barley ditelosomic addition line 7HL
mar
isolated among plants from the BC1F6 progeny of a barley-wheat amphiploid was studied, which in this work corresponds to BC2F10 and BC2F11 progeny. It was ascertained that when grown in the field, these alloplasmic lines manifest stable self-fertility. Plants
of the given lines are characterized by low height, shortened ears, the fewer number of stems and ears, and of spikelets in
the ear, by decreased grain productivity and weight of 1000 grains, in comparison with the common wheat cultivar Pyrotrix
28. The inhibition of trait expression in alloplasmic wheat-barley substitution and addition lines may be connected not only
with the influence of wild barley chromosomes functioning in the genotypic environment of common wheat, but also with the
effect of the barley cytoplasm. The alloplasmic line with substitution of chromosomes 1H
mar
(1B), 5H
mar
(5D), and 7H
mar
(7D) or the alloplasmic line 5HL
mar
with ditelosomic addition have, in comparison with the common wheat cultivar Pyrotrix 28, an increased grain protein content,
which is explained by the effect of wild barley H. marinum subsp. gussoneanum chromosomes. 相似文献
14.
Isabelle Sgalas Yann Prigent Daniel Davoust Bernard Bodo Sylvie Rebuffat 《Biopolymers》1999,50(1):71-85
The three‐dimensional solution structure of harzianin HC IX, a peptaibol antibiotic isolated from the fungus Trichoderma harzianum, was determined using CD, homonuclear, and heteronuclear two‐dimensional nmr spectroscopy combined with molecular modeling. This 14‐residue peptide, Ac Aib1 Asn2 Leu3 Aib4 Pro5 Ala6 Ile7 Aib8 Pro9 Iva10 Leu11 Aib12 Pro13 Leuol14 (Aib, α‐aminoisobutyric acid; Iva, isovaline; Leuol, leucinol), is a main representative of a short‐sequence peptaibol class characterized by an acetylated N‐terminus, a C‐terminal amino alcohol, and the presence of three Aib‐L ‐Pro motifs at positions 4–5, 8–9, and 12–13, separated by two dipeptide units. In spite of a lower number of residues, compared to the 18/20‐residue peptaibols such as alamethicin, harzianin HC IX exhibits remarkable membrane‐perturbing properties. It interacts with phospholipid bilayers, increasing their permeability and forming voltage‐gated ion channels through a mechanism slightly differing from that proposed for alamethicin. Sequence‐specific 1H‐ and 13C‐nmr assignments and conformational nmr parameters (3JNHCαH coupling constants, quantitative nuclear Overhauser enhancement data, temperature coefficients of amide and carbonyl groups, NH–ND exchange rates) were obtained in methanol solution. Sixty structures were calculated based on 98 interproton distance restraints and 6 Φ dihedral angle restraints, using high temperature restrained molecular dynamics and energy minimization. Thirty‐seven out of the sixty generated structures were consistent with the nmr data and were convergent. The peptide backbone consists in a ribbon of overlapping β‐turns twisted into a continuous spiral from Asn2 to Leuol14 and forming a 26 Å long helix‐like structure. This structure is slightly amphipathic, with the three Aib–Pro motifs aligned on the less hydrophobic face of the spiral where the Asn2 side chain is also present, while the more hydrophobic bulky side chains of leucines, isoleucine, isovaline, and leucinol are located on the concave side. The repetitive (Xaa–Yaa–Aib–Pro) tetrapeptide subunit, making up the peptide sequence, is characterized by four sets of (Φ,Ψ) torsional angles, with the following mean values: Φi = −90°, Ψi = −27°; Φi+1 = −98°, Ψi+1 = −17°; Φi+2 = −49°, Ψi+2 = −50°; Φi+3 = −78°, Ψi+3 = +3°. We term this particular structure, specifically occurring in the case of (Xaa–Yaa–Aib–Pro)n sequences, the (Xaa–Yaa–Aib–Pro)‐β‐bend ribbon spiral. It is stabilized by 4 → 1 intramolecular hydrogen bonds and differs from both the canonical 310‐helix made of a succession of type III β‐turns and from the β‐bend ribbon spiral that has been described in the case of (Aib–Pro)n peptide segments. © 1999 John Wiley & Sons, Inc. Biopoly 50: 71–85, 1999 相似文献
15.
A. V. Kalinovich N. V. Azarkina T. V. Vygodina T. Soulimane A. A. Konstantinov 《Biochemistry. Biokhimii?a》2010,75(3):342-352
Cytochrome c oxidase of the ba
3-type from Thermus thermophilus does not interact with cyanide in the oxidized state and acquires the ability to bind heme iron ligands only upon reduction.
Cyanide complexes of the reduced heme a
3 in cytochrome ba
3 and in mitochondrial aa
3-type cytochrome oxidase are similar spectroscopically, but the a
32+-CN complex of cytochrome ba
3 is strikingly tight. Experiments have shown that the K
d value of the cytochrome ba
3 complex with cyanide in the presence of reductants of the enzyme binuclear center does not exceed 10−8 M, which is four to five orders of magnitude less than the K
d of the cyanide complex of the reduced heme a
3 of mitochondrial cytochrome oxidase. The tightness of the cytochrome ba
3 complex with cyanide is mainly associated with an extremely slow rate of the ligand dissociation (k
off ≤ 10−7 sec−1), while the rate of binding (k
on ∼ 102 M−1·sec−1) is similar to the rate observed for the mitochondrial cytochrome oxidase. It is proposed that cyanide dissociation from
the cytochrome ba
3 binuclear center might be hindered sterically by the presence of the second ligand molecule in the coordination sphere of
CuB2+. The rate of cyanide binding with the reduced heme a
3 does not depend on pH in the neutral area, but it approaches linear dependence on H+ activity in the alkaline region. Cyanide binding appears to be controlled by protonation of an enzyme group with pK
a = 8.75. 相似文献
16.
Kirti Dhingra Petra Fousková Goran Angelovski Martin E. Maier Nikos K. Logothetis Éva Tóth 《Journal of biological inorganic chemistry》2008,13(1):35-46
Two new bismacrocyclic Gd3+ chelates containing a specific Ca2+ binding site were synthesized as potential MRI contrast agents for the detection of Ca2+ concentration changes at the millimolar level in the extracellular space. In the ligands, the Ca2+-sensitive BAPTA-bisamide central part is separated from the DO3A macrocycles either by an ethylene (L1) or by a propylene (L2) unit [H4BAPTA is 1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid; H3DO3A is 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid]. The sensitivity of the Gd3+ complexes towards Ca2+ and Mg2+ was studied by 1H relaxometric titrations. A maximum relaxivity increase of 15 and 10% was observed upon Ca2+ binding to Gd2L1 and Gd2L2, respectively, with a distinct selectivity of Gd2L1 towards Ca2+ compared with Mg2+. For Ca2+ binding, association constants of log K = 1.9 (Gd2L1) and log K = 2.7 (Gd2L2) were determined by relaxometry. Luminescence lifetime measurements and UV–vis spectrophotometry on the corresponding Eu3+ analogues proved that the complexes exist in the form of monohydrated and nonhydrated species; Ca2+ binding in the central part of the ligand induces the formation of the monohydrated state. The increasing hydration number
accounts for the relaxivity increase observed on Ca2+ addition. A 1H nuclear magnetic relaxation dispersion and 17O NMR study on Gd2L1 in the absence and in the presence of Ca2+ was performed to assess the microscopic parameters influencing relaxivity. On Ca2+ binding, the water exchange is slightly accelerated, which is likely related to the increased steric demand of the central
part leading to a destabilization of the Ln–water binding interaction.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
17.
Improved Bulk Materials with Thermoelectric Figure‐of‐Merit Greater than 1: Tl10–xSnxTe6 and Tl10–xPbxTe6
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Noting the steadily worsening problem of depleted fossil fuel sources, alternate energy sources have become increasingly important; these include thermoelectrics, which may use waste heat to generate electricity. To be economically viable, the thermoelectric figure‐of‐merit, zT, which is related to the energy conversion efficiency, needs to be in excess of unity (zT > 1). Tl4SnTe3 and Tl4PbTe3 were reported to attain a thermoelectric figure‐of‐merit zT max = 0.74 and 0.71, respectively, at 673 K. Here, the thermoelectric properties of both materials are presented as a function of x in Tl10–x Sn x Te6 and Tl10–x Pb x Te6, with x varying between 1.9 and 2.05, culminating in zT values in excess of 1.2. These materials are charge balanced when x = 2, according to (Tl+)8(Sn2+)2(Te2?)6 and (Tl+)8(Pb2+)2(Te2?)6 (or: (Tl+)4Pb2+(Te2?)3). Increasing x causes an increase in valence electrons, and thus a decrease in the dominating p‐type charge carriers. Larger x values occur with a smaller electrical conductivity and a larger Seebeck coefficient. In each case, the lattice thermal conductivity remains under 0.5 W m?1 K?1, resulting in several samples attaining the desired zT max > 1. The highest values thus far are exhibited by Tl8.05Sn1.95Te6 with zT = 1.26 and Tl8.10Pb1.90Te6 with zT = 1.46 around 685 K. 相似文献
18.
Ettore Benedetti Benedetto Di Blasio Vincenzo Pavone Carlo Pedone Gabriel Germain Murray Goodman 《Biopolymers》1979,18(3):517-522
C24H34N2O9, orthorhombic, P212121; a = 39.432 (10), b = 14.061 (5), c = 4.850 (2) Å, M = 494 a.m.u., Z = 4, Dm = 1.22 g cm?3, Dx = 1.22 g cm?3, R = 0.13 for 1205 observed reflections after refinement with isotropic thermal factors. The urethane and amide bonds are in the trans configuration, as well as all the ester groups. The φ and ψ angles of the L -glutamyl residues fall in the β-structure region of the Ramachandran's plot; the molecule is rather flat with the amide plane almost parallel to the c axis along which two hydrogen bonds hold the molecules together to form long rows in a “parallel pleated-sheet” fashion. 相似文献
19.
Stephen Murray Philip Bliss Najma Karim John Calam Graham W. Taylor 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2000,739(2)
A gas chromatography–electron capture mass spectrometry assay has been developed for the histamine H3 receptor agonist, Nα-methylhistamine (Nα-MH). The assay is linear from 50 pg–10 ng, with a limit of detection of 50 pg/ml for gastric juice and plasma, and 50 pg/sample for bacteria (107–108 CFU) and gastric tissue (5–10 mg wet weight). The limits of quantification are 100 pg/ml for gastric juice (%RSD=1.4) and plasma (%RSD=9.4), and 100 pg/sample for bacteria (%RSD=3.9) and tissue (%RSD=5.8). Nα-MH was not present in human plasma, but low levels (1.4 ng/ml and 0.4 ng/ml) were detected in two samples of human gastric juice obtained from patients infected with Helicobacter pylori. 相似文献
20.
Andrey Tatarenkov Rita B. Jnsson Lena Kautsky Kerstin Johannesson 《Journal of phycology》2007,43(4):675-685
Recent studies showing consequences of species’ genetic diversity on ecosystem performance raise the concern of how key ecosystem species are genetically structured. The bladder wrack Fucus vesiculosus L. is a dominant species of macroalga in the northern Atlantic, and it is particularly important as a habitat‐forming species in the Baltic Sea. We examined the genetic structure of populations of F. vesiculosus with a hierarchical approach from a within‐shore scale (10 m) to a between‐seas scale (Baltic Sea–Skagerrak, 800 km). Analysis of five microsatellite loci showed that population differentiation was generally strong (average FST = 12%), being significant at all spatial scales investigated (101, 103, 104–5, 106 m). Genetic differentiation between seas (Baltic Sea and Skagerrak) was substantial. Nevertheless, the effects of isolation by distance were stronger within seas than between seas. Notably, Baltic summer‐reproducing populations showed a strong within‐sea, between‐area (70 km) genetic structure, while Baltic autumn‐reproducing populations and Skagerrak summer‐reproducing populations revealed most genetic diversity between samples within areas (<1 km). Despite such differences in overall structure, Baltic populations of summer‐ and autumn‐reproducing morphs did not separate in a cluster analysis, indicating minor, if any, barriers to gene flow between them. Our results have important implications for management and conservation of F. vesiculosus, and we raise a number of concerns about how genetic variability should be preserved within this species. 相似文献