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941.
The conformational space of methyl 6-O-[(R)- and (S)- 1-carboxyethyl]-α-D-galactopyranoside has been investigated. A grid
search employing energy minimization at each grid point over the three major degrees of freedom, namely φ, ψ and ω, identified
low energy regions. The R-isomer shows five low energy conformers within ca. 1 kcal mol−1 of the global energy minimum. The
S-isomer has two conformers within a few tenths of a kcal mol−1 of the global energy minimum. Langevin dynamics simulations
have been have been performed at 300 K for 30 ns of each isomer. The φ dihedral angle has as its major conformer (g−1) for
the R-isomer whereas it is the (g+) conformer for the S-isomer. For the ψ dihedral angle the (t) conformer has the highest
population for both isomers. The dihedral angle ω has the (g+) conformer most highly populated, both for the R- and S-isomer.
The above five and two conformational states for the R- and S-isomers, respectively, make up 90% in each case of the populated
states during the Langevin dynamics (LD) simulations. Rate constants for the ω dihedral angle have been calculated based on
a number correlation function. Three bond homo- and heteronuclear, i.e. proton and carbon-13, coupling constants have been
calculated from the dynamics trajectories for comparison to experimental values. The heteronuclear coupling constant H2′,C6
has been measured for the S-isomer and found to be 3.3 Hz. The J value calculated from the LD simulations, namely 2.6 Hz,
is in fair agreement with experiment. A comparison to the X-ray structure of the R-isomer shows that the conformation of the
crystalline compound occupies the low energy region most highly populated as a single R-conformer (30%) during the LD simulations.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
942.
The clonal shrub, Mahonia aquifolium, is an aggressive invader of some forests in central Germany. We analysed the importance of seedling recruitment for the
local dynamics of these invasive populations. In contrast to many other clonal plants, repeated seedling recruitment takes
place in M. aquifolium, contributing to the colonization of available space within populations. Thus, sexual reproduction is not only important
for dispersal to new sites but also for the local invasion␣process. In situations with grass competition (Calamagrostis epigejos) the number of successful recruits is reduced, and clonal growth is the predominant mode of reproduction. Since seedling
recruitment results in an increasing number of genets as well as ramets, the investigated populations are still below their
carrying capacities. Seedling densities are higher beneath the canopy of adults than outside adult patches, and increase with
increasing cover of adult ramets. The spatially clumped pattern of seedling emergence results in density-dependent mortality
especially in the most crowded seedling clusters. However, adult neighbourhood imposes a much higher mortality. Therefore,
we expect that the importance of seedling recruitment for the dynamics of local M. aquifolium populations will decline as the invasion process continues.
Received: 15 January 1996 / Accepted: 28 September 1996 相似文献
943.
Neal R. Pellis Thomas J. Goodwin Diana Risin Bradley W. McIntyre Roland P. Pizzini David Cooper Tacey L. Baker Glenn F. Spaulding 《In vitro cellular & developmental biology. Animal》1997,33(5):398-405
Summary Immunity relies on the circulation of lymphocytes through many different tissues including blood vessels, lymphatic channels,
and lymphoid organs. The ability of lymphocytes to traverse the interstitium in both nonlymphoid and lymphoid tissues can
be determined in vitro by assaying their capacity to locomote through Type I collagen. In an attempt to characterize potential causes of microgravity-induced
immunosuppression, we investigated the effects of simulated microgravity on human lymphocyte function in vitro using a specialized rotating-wall vessel culture system developed at the Johnson Space Center. This very low shear culture
system randomizes gravitational vectors and provides an in vitro approximation of microgravity. In the randomized gravity of the rotating-wall vessel culture system, peripheral blood lymphocytes
did not locomote through Type I collagen, whereas static cultures supported normal movement. Although cells remained viable
during the entire culture period, peripheral blood lymphocytes transferred to unit gravity (static culture) after 6 h in the
rotating-wall vessel culture system were slow to recover and locomote into collagen matrix. After 72 h in the rotating-wall
vessel culture system and an additional 72 h in static culture, peripheral blood lymphocytes did not recover their ability
to locomote. Loss of locomotory activity in rotating-wall vessel cultures appears to be related to changes in the activation
state of the lymphocytes and the expression of adhesion molecules. Culture in the rotating-wall vessel system blunted the
ability of peripheral blood lymphocytes to respond to polyclonal activation with phytohemagglutinin. Locomotory response remained
intact when peripheral blood lymphocytes were activated by anti-CD3 antibody and interleukin-2 prior to introduction into
the rotating-wall vessel culture system. Thus, in addition to the systemic stress factors that may affect immunity, isolated
lymphocytes respond to gravitational changes by ceasing locomotion through model interstitium. These in vitro investigations suggest that microgravity induces non-stress-related changes in cell function that may be critical to immunity.
Preliminary analysis of locomotion in true microgravity revealed a substantial inhibition of cellular movement in Type I collagen.
Thus, the rotating-wall vessel culture system provides a model for analyzing the microgravity-induced inhibition of lymphocyte
locomotion and the investigation of the mechanisms related to lymphocyte movement. 相似文献
944.
Cacang Suarna Roger T. Dean Peter T. Southwell-Keeley Douglas E. Moore Roland Stocker 《Free radical research》1997,27(4):397-408
In previous work we demonstrated that up to 30 % of cholesteryl linoleate in homogenates of advanced human plaque samples is present in oxidized forms. Here we show that the material from plaque hexane extracts which co-elutes with cholesteryl hydroxylinoleate on reversed phase HPLC (Anal Biochem 1993;213:79), is composed of several isomers of cholesteryl hydroxy- and cholesteryl oxo-octadecadienoate. Enzymatic hydrolysis and measurement of liberated cholesterol and disappearance of the esters revealed that almost all of the material consisted of unoxidized cholesterol esterified to oxidized derivatives of octadeca-dienoate. Semi-preparative reversed-phase HPLC was used to obtain sufficient quantities of this co-eluting material to undertake normal phase HPLC separation of these components. The nature of such separated and isolated compounds was identified, by co-chromatography with authentic standards, UV spectroscopy and chemical ionization and electron impact mass spectrometry, as cholesteryl hydroxy- and cholesteryl oxo-octadecadienoate. These oxidized fatty acids have been observed previously in plaque, in agreement with our new unambiguous demonstration of their presence as cholesteryl esters. The application of the methods described for the separation of the various forms of oxidized cholesteryl octadecadienoate may aid mechanistic studies of in vitro and in vivo lipoprotein lipid oxidation. 相似文献
945.
Roland Peter 《当今生物学》2004,34(4):220-228
946.
Roland Wacker Stanka Stoeva Karola Pfüller Uwe Pfüller Wolfgang Voelter 《Journal of peptide science》2004,10(3):138-148
The complete primary structure of the A chain of mistletoe lectin III (ML3A), a type II ribosome-inactivating protein, was determined using proteolytic digests of ML3A, HPLC separation of the peptides, Edman degration and MALDI-MS. Based on our results, ML3A consists of 254 amino acid residues, showing a high homology to the A chain of isolectin ML1 with only 24 amino acid residue exchanges. A striking important structural difference compared with ML1A is the lack of the single N-glycosylation site in ML3A due to an amino acid exchange at position 112 (ML1A: NL112GS ==> ML3A: T112GS). The alignment of ML3A with the A chains of ML1, isoabrins, ricin D, Ricinus communis agglutinin and three lectins, identified from the Korean mistletoe Viscum album ssp. coloratum, demonstrates the rigid conservation of all amino acid residues, responsible for the RNA-N-glycosidase activity as reported for ricin D. In addition, the fully determined primary structure of ML3A will give further information about the biological mechanism of mistletoe lectin therapy. 相似文献
947.
948.
Current alarm systems in intensive care units create a very high rate of false positive alarms because most of them simply compare physiological measurements to fixed thresholds. An improvement can be expected when the actual measurements are replaced by smoothed estimates of the underlying signal. However, classical filtering procedures are not appropriate for signal extraction, as standard assumptions, such as stationarity, do no hold here: the time series measured often show long periods without change, but also upward or downward trends, sudden shifts and numerous large measurement artefacts. Alternative approaches are needed to extract the relevant information from the data, i.e., the underlying signal of the monitored variables and the relevant patterns of change, such as abrupt shifts and trends. This article reviews recent research on filter-based online signal extraction methods designed for application in intensive care. 相似文献
949.
Pascale Hubert Roland Greimers Elizabeth Franzen-Detrooz Jean Doyen Pierre Delanaye Jacques Boniver Philippe Delvenne 《Cancer immunology, immunotherapy : CII》1998,47(2):81-89
Dendritic cells (DC) are the most efficient antigen presenting cells. The clinical use of DC as vectors for antitumor and
anti-infectious disease immunotherapy has been limited by their low level and accessibility in normal tissue. Substantial
numbers of DC can be generated from peripheral blood cultured in the presence of interleukin-4 (IL-4) and granulocyte/macrophage-colony-stimulating
factor (GM-CSF). We showed in this study that substantial numbers of DC can be obtained from the peripheral blood of patients
with (pre)neoplastic lesions of the uterine cervix. The procedure required relatively small blood samples (10 ml) and the
presence of 100 U/ml IL-4 and 800 U/ml GM-CSF in the culture medium. There was no significant difference in the morphology,
yield, phenotype and function of generated DC between patients with cervical (pre)neoplastic lesions and healthy individuals.
When the hematopoietic factor Flt3 ligand (Flt3L, 40 ng/ml) was added, there was an average increase in the DC population
of 26% compared to cultures with GM-CSF and IL-4 alone. Approximately 1.2 × 106 cells with the characteristics of dendritic cells could be obtained when Flt3L was included in the medium. The addition of
Flt3L did not modify the phenotypic profile of DC (HLA-DR+, CD1a+, CD4+, CD54+, CD80+, CD86+, CD40+, CD3− and CD14−). In addition, Flt3L generated functional DC capable of stimulating the proliferation of alloreactive T cells. These results
suggest that Flt3L, in association with GM-CSF and IL-4, provides an advantageous tool for the large-scale generation of DC
and that an immunotherapy based on the use of DC generated in vitro is possible in patients with (pre)neoplastic lesions of
the uterine cervix.
Received: 8 January 1998 / Accepted: 30 April 1998 相似文献
950.
The iron requirement of four strains of lactobacilli (L. acidophilus, L. delbrueckii subsp. bulgaricus, L. plantarum, and L. pentosus) was studied in a synthetic medium under aerobic or anaerobic conditions. Effects of iron salt and iron-chelated compounds
were tested on bacterial growth in manganese-free or -supplemented media. No significant growth stimulation was observed in
any condition. These results support the absolute manganese requirement for optimum growth of lactobacilli and the needless
incorporation of iron in growth media.
Received: 5 November 1997 / Accepted: 20 January 1998 相似文献