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1.
Bressloff PC 《Journal of mathematical biology》2000,40(2):169-198
We study the existence and stability of traveling waves and pulses in a one-dimensional network of integrate-and-fire neurons
with synaptic coupling. This provides a simple model of excitable neural tissue. We first derive a self-consistency condition
for the existence of traveling waves, which generates a dispersion relation between velocity and wavelength. We use this to
investigate how wave-propagation depends on various parameters that characterize neuronal interactions such as synaptic and
axonal delays, and the passive membrane properties of dendritic cables. We also establish that excitable networks support
the propagation of solitary pulses in the long-wavelength limit. We then derive a general condition for the (local) asymptotic
stability of traveling waves in terms of the characteristic equation of the linearized firing time map, which takes the form
of an integro-difference equation of infinite order. We use this to analyze the stability of solitary pulses in the long-wavelength
limit. Solitary wave solutions are shown to come in pairs with the faster (slower) solution stable (unstable) in the case
of zero axonal delays; for non-zero delays and fast synapses the stable wave can itself destabilize via a Hopf bifurcation.
Received: 27 October 1998 相似文献
2.
Wan C La Y Zhu H Yang Y Jiang L Chen Y Feng G Li H Sang H Hao X Zhang G He L 《Amino acids》2007,32(1):101-108
Summary. In this study we focused on detecting schizophrenia related changes of plasma proteins using proteomic technology and examining
the relation between schizophrenia and haptoglobin (Hp) genotype. We investigated plasma proteins from schizophrenic subjects (n = 42) and healthy controls (n = 46) by two-dimensional gel electrophoresis (2-DE) in combination with mass spectrometry. To further reveal the genetic
relationship between acute phase proteins (APPs) and schizophrenia disease, we tested Hp α1/Hp α2 (Hp 1/2) polymorphism and two single nucleotide polymorphisms (SNPs) of Hp, rs2070937 and rs5473, for associations with schizophrenia in the Chinese Han population. With the relatively high number
of samples for 2-DE work, we found that four proteins in the family of positive APPs were all up-regulated in patients. In
genetic association study, we found significant associations existing between schizophrenia and Hp polymorphisms, Hp 1/2 and rs2070937 variants. Schizophrenia is accompanied by both an altered expression of Hp protein and a different genotype
distribution of Hp gene, demonstrating that Hp is associated with schizophrenia. The results from proteomic and genomic aspects both indicate
that acute phase reaction is likely to be an aetiological agent in the pathophysiology of schizophrenia, but not just an accompanying
symptom. The positive APPs are schizophrenic related proteins, with the highly concordant results on four positive APPs.
The first two authors contributed equally. 相似文献
3.
Summary. Ten years after the establishment of the term proteome, the science surrounding it has yet to fulfill its potential. While
a host of technologies have generated lists of protein names, there are only a few reported studies that have examined the
individual proteins at the covalent chemical level defined as protein species in 1997 and their function. In the current study,
we demonstrate that this is possible with two-dimensional gel electrophoresis (2-DE) and mass spectrometry by presenting clear
evidence of in vivo N-terminal alpha A crystallin truncation and relating this newly detected protein species to alpha crystallin
activity regulation by protease cleavage in the healthy young murine lens. We assess the present state of technology and suggest
a shift in resources and paradigm for the routine attainment of the protein species level in proteomics. 相似文献
4.
5.
Mühling J Nickolaus KA Matejec R Langefeld TW Harbach H Engel J Wolff M Weismüller K Fuchs M Welters ID Krüll M Heidt MC Hempelmann G 《Amino acids》2008,34(2):257-270
We examined the effects of beta-alanine (taurine analogue and taurine transport antagonist), taurine (regarding its role in neutrophil (PMN) immunonutrition) and taurine combined either with L-NAME (inhibitor of *NO-synthase), SNAP (*NO donor), DON (glutamine-analogue and inhibitor of glutamine-requiring enzymes), DFMO (inhibitor of ornithine-decarboxylase) and beta-alanine on neutrophil amino- and alpha-keto acid profiles or important PMN immune functions in order to establish whether taurine transport-, nitric oxide-, glutamine- or ornithine-dependent mechanisms are involved in any of the taurine-induced effects. According to the present findings, the taurine-mediated effect appears to be based primarily on a modulation of important transmembraneous transport mechanisms and only secondarily on directly or indirectly induced modifications in intragranulocytic amino- and alpha-keto acid homoeostasis or metabolism. Although a direct relation to the parallel observed immunological modifications can only be presumed, these results show very clearly that compositional modifications in the free intragranulocytic amino- and alpha keto-acid pools coinciding with changes in intragranulocytic taurine levels are relevant metabolic determinants that can significantly influence the magnitude and quality of the granulocytic immune response. 相似文献
6.
N.E. El Houssif 《Journal of mathematical biology》2001,42(5):424-438
In this paper we model the population dynamics of the worm Nais elinguis, which reproduces by division into two unequal parts. By using renewal theory we derive the asymptotic behaviour of a Naidis elinguis population. In particular we prove a certain relation between the fraction of the population that was born small (respectively
the fraction that was born large) and the inter-division times.
Received 20 January 1999 / Revised version: 1 August 1999?Published online: 10 April 2001 相似文献
7.
Summary. 3-Hydroxynorvaline (HNV; 2-amino-3-hydroxypentanoic acid), a microbial L-threonine analogue, is toxic to mammalian cells and
displays antiviral properties. In view of this, we investigated the toxicity and/or potential teratogenicity of HNV in developing
chicken and mouse embryos. HNV was administered to chicken embryos (in ovo; dose 75–300 μmole/egg; 48 h post-incubation) and pregnant Hanover NMRI mice (per os; total dose 900–1800 mg/kg body mass; gestation days 7–9). Control animals received sterile saline solutions. Harvested embryos
(chicken embryos, 10 days post-incubation; mouse embryos; gestation day 18) were fixed in glutaraldehyde and stereomicroscopically
inspected for signs of dysmorphogenesis. Body mass, body and toe length and mortality of chicken embryos, and the body mass
and mortality of mouse embryos were recorded. HNV exposure significantly increased the incidence of embryotoxic (growth retardation,
toxic mortality) and congenital defects in both chicken and mouse embryos. All the observed effects were dose-dependent. In
conclusion, HNV is an embryotoxic and teratogenic compound, which caused significant developmental delay and congenital defects
in developing chicken and mouse embryos. 相似文献
8.
A single-species population dynamics with dispersal in a spatially heterogeneous environment is modeled by a nonlinear reaction-diffusion equation with a potential term. To each nonlinear kinetics there corresponds a bifurcation curve that describes the relation between the growth rate and the central density of a steady-state population distribution. Our main concern is an inverse problem for this correspondence. The existence of nonlinear kinetics realizing a prescribed bifurcation curve is established. It is shown that the freedom of such kinetics is of degree finite and even, depending only on the heterogeneity of the environment, and conversely that any nonnegative even integer occurs as the degree of freedom in some environments. A discussion is also made on under what kind of environment the degree is equal to zero or is positive. The mathematical analysis involves the development of a general theory for singular multiplicative Wiener-Hopf integral equations. 相似文献
9.
Summary. Isoprostanes, non-enzymatic peroxidation products of arachidonic acid, are attractive biomarkers of oxidative stress in research
in biology, medicine and nutrition. For the appropriate use of biomarkers it is required that these are both biologically
and technically valid. Whereas the biological validity of isoprostanes is well-established, it is technically quite complicated
to measure isoprostanes and its metabolites in body fluids, and its rapid disappearance from plasma may hamper practical application.
This paper shortly introduces isoprostanes as a biomarker for studies with humans, describes a novel fast and sensitive method
for measuring isoprostanes in plasma by high-performance liquid chromatography and tandem mass spectrometry, and provides
several examples of the use of the method in studies in humans. By taking care of the biological and technical validity of
this biomarker it is possible to establish the antioxidant effects of some food ingredients in studies with human volunteers. 相似文献
10.
Summary. In this paper, the analog of arginine residues in peptides was synthesized and characterized by ESI-MS/MS (electrospray ionization
with tandem mass spectrometry), 31P NMR, 1H NMR, IR and high-resolution mass spectrometry. When the Todd reaction activity of the guanidino group in free arginine and
the arginine peptide analog were compared, it was found that the proton affinity of the guanidino group was decreased when
both the N- and the C-terminal were blocked. As a result, the guanidino group of arginine residues in peptides could be phosphorylated
under the Todd reaction condition, but not the free arginine. This result was further proved by the theoretical calculation
of their proton affinity. 相似文献
11.
Polyamines and abiotic stress: recent advances 总被引:8,自引:0,他引:8
Summary. In this review we will concentrate in the results published the last years regarding the involvement of polyamines in the
plant responses to abiotic stresses, most remarkably on salt and drought stress. We will also turn to other types of abiotic
stresses, less studied in relation to polyamine metabolism, such as mineral deficiencies, chilling, wounding, heavy metals,
UV, ozone and paraquat, where polyamine metabolism is also modified.
There is a great amount of data demonstrating that under many types of abiotic stresses, an accumulation of the three main
polyamines putrescine, spermidine and spermine does occur. However, there are still many doubts concerning the role that polyamines
play in stress tolerance. Several environmental challenges (osmotic stress, salinity, ozone, UV) are shown to induce ADC activity
more than ODC. The rise in Put is mainly attributed to the increase in ADC activity as a consequence of the activation of
ADC genes and their mRNA levels. On the other hand, free radicals are now accepted as important mediators of tissue injury
and cell death. The polycationic nature of polyamines, positively charged at physiological pH, has attracted the attention
of researchers and has led to the hypothesis that polyamines could affect physiological systems by binding to anionic sites,
such as those associated with nucleic acids and membrane phospholipids. These amines, involved with the control of numerous
cellular functions, including free radical scavenger and antioxidant activity, have been found to confer protection from abiotic
stresses but their mode of action is not fully understood yet. In this review, we will also summarize information about the
involvement of polyamines as antioxidants against the potential abiotic stress-derived oxidative damage.
Authors’ address: Dr. María Patricia Benavides, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956,
Buenos Aires 1113, Argentina 相似文献
12.
Summary. The eye lens is a fascinating organ as it is in essence living transparent matter. Lenticular transparency is achieved through
the peculiarities of lens morphology, a semi-apoptotic process where cells elongate and loose their organelles and the precise
molecular arrangement of the bulk of soluble lenticular proteins, the crystallins. The 16 crystallins ubiquitous in mammals
and their modifications have been extensively characterized by 2-DE, liquid chromatography, mass spectrometry and other protein
analysis techniques. The various solubility dependant fractions as well as subproteomes of lenticular morphological sections
have also been explored in detail. Extensive post translational modification of the crystallins is encountered throughout
the lens as a result of ageing and disease resulting in a vast number of protein species. Proteomics methodology is therefore
ideal to further comprehensive understanding of this organ and the factors involved in cataractogenesis. 相似文献
13.
In this paper a mathematical model is developed to describe the effect of nonuniform growth on the mechanical stress experienced
by cells within an avascular tumour. The constitutive law combines the stress-strain relation of linear elasticity with a
growth term that is derived by analogy with thermal expansion. To accommodate the continuous nature of the growth process,
the law relates the rate of change of the stress tensor to the rate of change of the strain (rather than relating the stress
to the strain directly). By studying three model problems which differ in detail, certain characteristic features are identified.
First, cells near the tumour boundary, where nutrient levels and cell proliferation rates are high, are under compression.
By contrast, cells towards the centre of the tumour, where nutrient levels are low and cell death dominant, are under tension.
The implications of these results and possible model developments are also discussed.
Received: 15 November 1999 / Published online: 5 May 2000 相似文献
14.
Cloning and heterologous expression of a rape cDNA encoding UDP-glucose:sinapate glucosyltransferase
A cDNA encoding a UDP-glucose:sinapate glucosyltransferase (SGT) that catalyzes the formation of 1-O-sinapoylglucose, was isolated from cDNA libraries constructed from immature seeds and young seedlings of rape (Brassica napus L.). The open reading frame encoded a protein of 497 amino acids with a calculated molecular mass of 55,970 Da and an isoelectric
point of 6.36. The enzyme, functionally expressed in Escherichia coli, exhibited broad substrate specificity, glucosylating sinapate, cinnamate, ferulate, 4-coumarate and caffeate. Indole-3-acetate,
4-hydroxybenzoate and salicylate were not conjugated. The amino acid sequence of the SGT exhibited a distinct sequence identity
to putative indole-3-acetate glucosyltransferases from Arabidopsis thaliana and a limonoid glucosyltransferase from Citrus unshiu, indicating that SGT belongs to a distinct subgroup of glucosyltransferases that catalyze the formation of 1-O-acylglucosides (β-acetal esters).
Received: 14 July 2000 / Accepted: 8 August 2000 相似文献
15.
Summary. Basic biological processes in which tissue transglutaminase (TG2, tTG) is thought to be important including apoptosis, cell
adhesion and migration, ECM homeostasis and angiogenesis are key stages in the multistage tumour progression cascade. Studies
undertaken with primary tumours and experimental models suggest that TG2 expression and activity in the tumour body and surrounding
matrix generally decreases with tumour progression, favouring matrix destabilisation, but supporting angiogenesis and tumour
invasion. In contrast, in the secondary metastatic tumour TG2 is often highly expressed whereby its potential roles in cell
survival both at the intra- and extracellular level become important. In the following review the underlying molecular basis
for the selection of these different phenotypes in tumour types and the anomaly for the requirement of TG2 is discussed in
relation to the complex events of tumour progression. 相似文献
16.
Summary. Human alpha-1-proteinase inhibitor is a well-characterized protease inhibitor with a wide spectrum of anti-protease activity.
Its major physiological role is inhibition of neutrophil elastase in the lungs, and its deficiency is associated with progressive
ultimately fatal emphysema. Currently in the US, only plasma-derived human alpha-1-proteinase inhibitor is available for augmentation
therapy, which appears to be insufficient to meet the anticipated clinical demand. Moreover, despite effective viral clearance
steps in the manufacturing process, the potential risk of contamination with new and unknown pathogens still exists. In response,
multiple efforts to develop recombinant versions of human alpha-1-proteinase inhibitor, as an alternative to the plasma-derived
protein, have been reported. Over the last two decades, various systems have been used to express the human gene for alpha-1-proteinase
inhibitor. This paper reviews the recombinant versions of human alpha-1-proteinase inhibitor produced in various hosts, considers
current major safety and efficacy issues regarding recombinant glycoproteins as potential therapeutics, and the factors that
are impeding progress in this area1.
1 The opinions expressed in this paper reflect the authors’ personal views, based on published data and the information available
from the public domains, and have no relation to the official statements, if any, held by the US FDA, National Institutes
of Health, or the US Department of Health and Human Services. FDA official recommendations for plasma protein therapeutics
and recombinant proteins regarding safety, purity, and potency of new drugs and biologics produced by recombinant DNA technology
are referred below as the US FDA Guidances. 相似文献
17.
Summary. Our aim was to determine changes in free amino acid (FAA) and dipeptide (DP) concentrations in probable Alzheimer’s disease
(pAD) subjects compared with control (CT) subjects using liquid chromatography and electrospray ionization tandem mass spectrometry
(LCMS2). We recruited gender- and age-matched study participants based on neurological and neuropsychological assessments. We measured
FAAs and DPs in cerebrospinal fluid (CSF), plasma and urine using LCMS2 with selected reaction monitoring (SRM). Imidazole-containing FAAs (histidine, methyl-histidine), catecholamines (L-DOPA
and dopamine), citrulline, ornithine, glycine and antioxidant DPs (carnosine and anserine) accounted for the major changes
between CT and pAD. Carnosine levels were significantly lower in pAD (328.4 ± 91.31 nmol/dl) than in CT plasma (654.23 ± 100.61 nmol/dl).
In contrast, L-DOPA levels were higher in pAD (1400.84 ± 253.68) than CT (513.10 ± 121.61 nmol/dl) plasma. These data underscore
the importance of FAA and DP metabolism in the pathogenesis of AD. Since our data show changes in antioxidants, neurotransmitters
and their precursors, or FAA associated with urea metabolism in pAD compared with CT, we propose that manipulation of these
metabolic pathways may be important in preventing AD progression. 相似文献
18.
Summary. To date, the majority of therapeutic peptides and proteins have to be administered via parenteral routes, which are painful
and inconvenient. In order to gain sufficient high blood concentrations after oral application, various barriers in the gastrointestinal
tract have to be overcome. Apart from a poor membrane uptake and intense enzymatic degradation, this study will demonstrate
that thiol–disulphide reactions are an underestimated essential part of the presystemic metabolism. Glutathione, integrative
part of the antioxidant defence system in the gastrointestinal tract, may play an important role in the inactivation of orally
given peptides and proteins. In order to verify this hypothesis, desmopressin which bears a single disulphide bond was used
as model peptide drug. Desmopressin was incubated with GSH in various concentrations, and the extent of thiol/disulphide exchange
reactions between the peptide drug and GSH was investigated in dependence on pH and ratio of reactants determined as a function
of time via HPLC, LC-MS and Maldi-Tof-MS analyses.
Results showed that desmopressin is degraded by 1% reduced glutathione at pH 4 and pH 5.5. In presence of 0.01%, 0.1% and
1% of reduced glutathione 6.1%, 19.4% and 52.1% of desmopressin, respectively, were degraded. The masses of the conjugates
after deconvolution measured by liquid chromatography and electrospray ionisation mass spectrometric detection were m/z 1069.67, m/z 1376.50, m/z 1683.40 and m/z 2138. These molecular masses, confirmed by Maldi-Tof-MS analysis, correspond with the masses of conjugates expected in theory.
Under defined conditions, these results reveal that thiol–disulphide exchange reactions have a considerable impact on the
alteration of peptide drugs and proteins. 相似文献
19.
Summary. Protein histidine phosphorylation is now recognized as an important form of post-translational modification. The acid-lability
of phosphohistidine has meant that this phosphorylation has not been as well studied as serine/threonine or tyrosine phosphorylation.
We show that phosphohistidine and phosphohistidine-containing phosphopeptides derived from proteolytic digestion of phosphohistone
H4 are detectable by ESI-MS. We also demonstrate reverse-phase HPLC separation of these phosphopeptides and their detection
by MALDI-TOF-MS. 相似文献
20.
Sahún I Gallego X Gratacòs M Murtra P Trullás R Maldonado R Estivill X Dierssen M 《Amino acids》2007,33(4):677-688
Summary. Sensitivity to pharmacological challenges has been reported in patients with panic disorder. We have previously validated
transgenic mice overexpressing the neurotrophin-3 (NT-3) receptor, TrkC (TgNTRK3), as an engineered murine model of panic
disorder. We could determine that TgNTRK3 mice presented increased cellularity in brain regions, such as the locus ceruleus,
that are important neural substrates for the expression of anxiety in severe anxiety states. Here, we investigated the sensitivity
to induce anxiety and panic-related symptoms by sodium lactate and the effects of various drugs (the α2-adrenoceptor antagonist,
yohimbine and the adenosine antagonist, caffeine), in TgNTRK3 mice. We found enhanced panicogenic sensitivity to sodium lactate
and an increased intensity and a differential pattern of Fos expression after the administration of yohimbine or caffeine
in TgNTRK3. Our findings validate the relevance of the NT-3/TrkC system to pathological anxiety and raise the possibility
that a specific set of fear-related pathways involved in the processing of anxiety-related information may be differentially
activated in panic disorder. 相似文献