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At least 1,243 records · Page 69Linked to original sources
PubMed2005

Three-dimensional in vivo magnetic resonance microscopy of beech (Fagus sylvatica L.) wood.

Spatial structure and water distribution in branch tissues after mechanical injury were investigated in vivo by three-dimensional (3D) magnetic resonance (MR) microscopy. On a beech tree (Fagus sylvatica L.), transplanted in a portable pot, a branch was topped and then MR imaged. High-resolution 3D MR images revealed structures which could not be identified by conventional MR images or by light microscopy. MR measurements confirmed our assumption that moisture content is decreasing towards the wounded part of the branch. This indicates that quick moisture loss from mechanically wounded tissues represents the initial passive response of compromised tissue.

Fagus↗
PubMed2006

Molecular cloning of a HMG-CoA reductase gene from Eucommia ulmoides Oliver.

The 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) catalyzes the conversion of HMG-CoA to mevalonate, which is the first committed step in the pathway for isoprenoid biosynthesis in plants. A full-length cDNA encoding HMGR (designated as EuHMGR, GenBank Accession No. AY796343) was isolated from Eucommia ulmoides by rapid amplification of cDNA ends (RACE). The full-length cDNA of EuHMGR comprises 2281 bp with a 1770-bp open reading frame (ORF) encoding a 590-amino-acid polypeptide with two trans-membrane domains revealed by bioinformatic analysis. Molecular modeling showed that EuHMGR is a new HMGR with a spatial structure similar to other plant HMGRs. The deduced protein has an isoelectric point (pI) of 6.89 and a calculated molecular weight of about 63 kDa. Sequence comparison analysis showed that EuHMGR had highest homology to HMGR from Hevea brasiliensis. As expected, phylogenetic tree analysis indicated that EuHMGR belongs to plant HMGR group. Tissue expression pattern analysis showed that EuHMGR is strongly expressed in the leaves and stems whereas it is only poorly expressed in the roots, which implies that EuHMGR may be a constitutively expressing gene. Functional complementation of EuHMGR in HMGR-deficient mutant yeast JRY2394 demonstrated that EuHMGR mediates the mevalonate biosynthesis in yeast.

Amino Acid Motifs↗
PubMed2005

Application of geostatistical methods to arsenic data from soil samples of the Cova dos Mouros mine (Vila Verde-Portugal).

A total of 286 soil samples were collected in the Cova dos Mouros area. All samples were dry sieved into the <200 mesh size fraction and analysed for Fe, Cu, Zn, Pb, Co, Ni, Bi and Mn by atomic absorption spectrometry (AAS) and for As, Se, Sb and Te by atomic absorption spectrometry-hydrid generation (AAS-HG). Only the results of arsenic are discussed in this paper although the survey was extended to all analysed chemical elements. The purpose of this study was to make a risk probability mapping for arsenic that would allow better knowledge about the vulnerability of the soil to arsenic contamination. To achieve this purpose, the initial variable was transformed into an indicator variable using as thresholds the risk-based standards (intervention values) for soils, as proposed by [Swartjes 1999. Risk based assessment of soil and groundwater quality in the Netherlands: Standards and remediation. J. Geochem. Explor.73 1-10]. To account for spatial structure, sample variograms were computed for the main directions of the sampling grid and a spherical model was fitted to each sample variogram (arsenic variable and indicator variables). The parameters of the spherical model fitted to the arsenic variable were used to predict arsenic concentrations at unsampled locations. A risk probability mapping was also done to assess the vulnerability of the soil towards the mining works. The parameters of the spherical model fitted to each indicator variable were used to estimate probabilities of exceeding the corresponding threshold. The use of indicator kriging as an alternative to ordinary kriging for the soil data of Cova dos Mouros produced unbiased probability maps that allowed assessment of the quality of the soil.

Arsenic↗
PubMed2006

Cloning and characterization of a root-specific expressing gene encoding 3-hydroxy-3-methylglutaryl coenzyme A reductase from Ginkgo biloba.

3-Hydroxy-3-methylglutaryl coenzyme A reductase (HMGR, EC: 1.1.1.34) catalyzes the first committed step in mevalonic acid (MVA) pathway for biosynthesis of isoprenoids. The full-length cDNA encoding HMGR was isolated from Ginkgo biloba for the first time (designated as GbHMGR, GenBank accession number AY741133), which contained a 1713 bp ORF encoding 571 amino acids. The GbHMGR genomic DNA sequence was also obtained, revealing GbHMGR had four exons and three introns. The deduced GbHMGR protein showed high identity to other plant HMGRs and contained two trans-membrane domains and a catalytic domain. The three dimensional model of GbHMGR represented a typical spatial structure of HMGRs. The Southern blot and RT-PCR assay results indicated that GbHMGR belonged to a small gene family, and expressed in a tissue-specific manner with a low level expression being only found in root. The potential significance of GbHMGR gene was also discussed.

Amino Acid Sequence↗
PubMed1981

Direction selectivity in human visual perception, investigated with low contrast gratings.

Velocity thresholds (VT's) of direction selective mechanism were measured with coarse low contrast gratings, visible only when moving. direction of movement was detected only in a movement perception domain (MPD), limited by upper and lower VT's and a minimum exposure time of movement. MPD expanded with increasing contrast or increasing stimulus area. MPD shifted towards higher velocities with lower spatial frequencies or with larger stimulus eccentricities. Form perception in MPD was best at optimal velocities; the spatial structure of the gratings was not evident at the VT level. These observations suggest a velocity tuned sensitivity of direction selective mechanisms and an association of movement and form perception with the activity of movement analysing neurons.

Differential Threshold↗
PubMed1986

The history of diclofenac.

The purpose in developing diclofenac sodium was to synthesize a nonsteroidal anti-inflammatory drug with high activity and outstanding tolerability. Factors considered were drug transport through biologic membranes, the atomic and spatial structure of the molecule, and the electronic structure. Based on analysis of other nonsteroidal anti-inflammatory drugs, it was postulated that an effective antirheumatic agent should have the following characteristics: an acidity constant between 4 and 5, a partition coefficient of approximately 10, and two aromatic rings twisted in relation to each other. The result was diclofenac sodium, which has an acidity constant of 4.0 and a partition coefficient of 13.4. The structural elements include a phenylacetic acid group, a secondary amino group, and a phenyl ring containing chlorine atoms, which cause maximum twisting of the ring. Experimental and clinical findings obtained to date have indicated that diclofenac sodium was synthesized on well-founded principles.

Chemical Phenomena↗
PubMed1979

Physicochemical studies of the protein-lipid interactions in melittin-containing micelles.

Complexes of melittin with detergents and phospholipids have been characterized by fluorescence, circular dichroism, ultracentrifugation, quasi-elastic light scattering and 1H nuclear magnetic resonance (NMR) experiments. By ultracentrifugation and quasi-elastic light-scattering measurements it is shown that melittin forms stoichiometrically well-defined complexes with dodecylphosphocholine micelles consisting of one melittin molecule and approximately forty detergent molecules. Evidence from fluorescence, circular dichroism and 1H nuclear magnetic resonance experiments indicates that the conformation of melittin bound to micelles of various detergents or of diheptanoyl phosphatidylcholine is largely independent of the type of lipid and furthermore appears to be quite closely related to the conformation of melittin bound to phosphatidylcholine bilayers. 1H NMR is used to investigate the conformation of micelle-bound melittin in more detail and to compare certain aspects of the melittin conformation in the micelles with the spatial structures of monomeric and self-aggregated tetrameric melittin in aqueous solution. The experience gained with this system demonstrates that high resolution NMR of complexes of membrane proteins with micelles provides a viable method for conformational studies of membrane proteins.

Bee Venoms↗
PubMed1989

Effects of bicuculline on signal detectability in lateral geniculate nucleus relay cells.

The lateral geniculate nucleus conveys the center-surround organized retinal receptive fields to the cortex in a way that does not significantly alter their spatial structure. However, non-retinal influences may change the 'strength' (detectability) of the signal under conditions of anesthesia, arousal and attention. A previous analysis of receiver operating characteristic curves in cat suggests that a reduction in signal detectability occurs in lateral geniculate nucleus (LGN) relay cells in anesthetized animals in comparison to the retinal afferents. In the present study, it was found that antagonism of GABAA receptors with bicuculline (BIC) increased signal detectability in LGN relay cells in the tree shrew (Tupaia belangeri). This change is consistent with the hypothesis that feedforward and/or feedback GABAergic circuits in the LGN differentially affect the retinogeniculate transfer ratio for visually driven activity versus maintained (spontaneous) activity. Under conditions of arousal or attention, signal detectability may be increased by brainstem activation, thus increasing the flow of information in the visual system.

Action Potentials↗
PubMed1990

Evoked alpha- and mu-rhythm in humans: a neuromagnetic study.

We present the results of a neuromagnetic study on the spatial structure of brain rhythms enhanced by photic and somatosensory stimulation, as measured on the occipital, rolandic and frontorolandic regions in humans. It emerges that, while it is always possible to drive the cerebral activity during sustained stimulation at any given frequency, only certain specific frequencies can produce prolonged synchronization (i.e. the oscillating activity elicited by the repetitive stimulation continues well beyond its termination). In both studied modalities we were able to localize equivalent sources for the synchronized responses; their relationship with the known evoked responses is discussed. In the visual modality the synchronization was characterized by a potentiation of the subjects' alpha-rhythm. In the somatosensory modality synchronization was reflecting two different activities: one probably related to the rolandic mu-rhythm, the second suggesting the presence of two widely separated and time correlated sources possibly driven by a unique, deep clock. Possible implications for other studies of the dominant brain rhythms, or experimental checks on specific brain models, as well as of the visual and somatosensory evoked responses are discussed.

Adult↗
PubMed1995

Investigation of EEG non-linearity in dementia and Parkinson's disease.

Many recent studies based on the surrogate data method failed to identify significant non-linearity in the EEG. In this study we examine whether the use of a different embedding method (spatial instead of time delay), and calculation of Kolmogorov entropy (K2) and the largest Lyapunov exponent (L1) in addition to the correlation dimension (D2), can distinguish the EEG form linearly filtered noise. We have calculated D2, L1 and K2 of original EEG epochs and surrogate (phase randomized) data in 9 control subjects, 9 demented patients and 13 Parkinson patients. The correlation dimension D2 and the largest Lyapunov exponent L1 could distinguish between the EEG tracings and the surrogate data. Demented patients had significantly lower D2 and L1 compared to controls. L1 was higher in Parkinson patients than in demented patients. Contrary to other studies that have used the Theiler surrogate data method, we find evidence for non-linearity in normal and abnormal EEG during the awake/eyes closed state. Apparently it is the spatial structure in the EEG that exhibits much of the non-linear structure. Furthermore, non-linear EEG measures show more or less specific patterns of dysfunction in dementia and Parkinson's disease.

Aged↗
PubMed1995

Differential effects of molecular chaperones on refolding of homologous proteins.

Three homologous aspartate aminotransferases with virtually identical spatial structures and pairwise amino acid sequence identities of > 40% differ markedly with respect to the yield of renaturation upon dilution from 6 M guanidine hydrochloride (mitochondrial << cytosolic < Escherichia coli). The enzymes also respond differently to molecular chaperones. GroEL/GroES, the Hsp60 homolog of E. coli, increased considerably the yield of renaturation of mitochondrial aspartate aminotransferase and to a lesser extent that of its cytosolic counterpart, but not that of the E. coli enzyme. DnaK/DnaJ/GrpE, the Hsp70 system of E. coli, also increased the yield of renaturation of mitochondrial aspartate aminotransferase. Apparently, specific features in the amino acid sequence or the folding pathway which are independent of the final secondary and tertiary structure determine the interactions of the folding proteins with the chaperone systems.

Animals↗
PubMed1996

5S rRNA sugar-phosphate backbone protection in complexes with specific ribosomal proteins.

5S ribosomal RNA forms stable specific complexes with ribosomal proteins L18, L25 and L5. In this work, interaction of phosphate residues of E. coli 5S rRNA within 5S rRNA-protein complexes has been studied. For this purpose 5S rRNA with statistically distributed phosphorothioate residues has been used for complex formation and the accessibility of phosphorothioates to iodine cleavage in the complex and in the free state has been studied. In free 5S rRNA, the phosphate residue at A73 was partially protected, probably due to being involved in the organization of the spatial structure of 5S rRNA. This protection is stronger in the complex with three proteins when the 5S rRNA structure is stabilized. In the 5S rRNA-L18 complex only two phosphate groups, G7 and A34, were protected. L25 in a complex with 5S rRNA protects large numbers of phosphorothioate groups concentrating in two clusters, indicating the possibility of two binding sites for this protein on 5S rRNA. The protection pattern differs from that for individual proteins because of the possible rearrangement of the structure.

Base Sequence↗
PubMed1980

Spread of cancer cells in tissues: modelling and simulation.

Continuing previous studies in which tumor diseases were interpreted as unstable control loops, the present paper tries to determine the spatial structure and the time behaviour of cell renewal systems. For this purpose a computer model for the two-dimensional cell space was developed, which is described by a set of specifications and growth statements. Selected case studies are then simulated by means of a digital computer (CYBER 76). The development of this model enables a deeper insight into the structure and function of disturbed cell renewal processes. Furthermore, it is possible with this computer model to simulate simple basic cases which, in reality, could hardly or not at all be tested.

Animals↗
PubMed1994

EXPLAN--a programming language for complex visual stimuli presentation.

Visual cognition research requires the flexible use of structured spatial patterns, characterized by various space and time parameters, which may be administered as visual stimuli. Dealing with this kind of study, we developed a special-purpose programming language and implemented a compiler to build executable programs. The language allows the presentation of stimuli, their space coordinates, persistency values, sequence, kinematic parameters, space-time proximity with other visual stimuli, determination of their modification according to external interaction, generation of subliminal stimuli, monitoring of different subject reactions, automatic reporting of stimulus presentation, and reaction monitoring. Such a language has been successfully utilized in a visual perception research.

Algorithms↗
PubMed1985

An evaluation of the combined use of nuclear magnetic resonance and distance geometry for the determination of protein conformations in solution.

An evaluation of the potential of nuclear magnetic resonance (n.m.r.) as a means of determining polypeptide conformation in solution is performed with the aid of a new distance geometry program which is capable of computing complete spatial structures for small proteins from n.m.r. data. Ten sets of geometric constraints which simulate the results available from n.m.r. experiments of varying precision and completeness were extracted from the crystal structure of the basic pancreatic trypsin inhibitor, and conformers consistent with these constraints were computed. Comparison of these computed structures with each other and with the original crystal structure shows that it is possible to determine the global conformation of a polypeptide chain from the distance constraints which are available from n.m.r. experiments. The results obtained with the different data sets also provide a standard by which the quality of protein structures computed from n.m.r. data can be evaluated when no crystal structure is available, and indicate directions in which n.m.r. experiments for protein structure determination could be further improved.

Animals↗
PubMed1991

Dynamic population epidemic models.

Most multipopulation epidemic models are of the contact distribution type, in which the locations of successive contacts are chosen independently from appropriate contact distributions. This paper is concerned with an alternative class of models, termed dynamic population epidemic models, in which infectives move among the populations and can infect only within their current population. Both the stochastic and deterministic versions of such models are considered. Their threshold behavior is analyzed in some depth, as are their final outcomes. Velocities of spread of infection are considered when the populations have a spatial structure. A criterion for finding the equivalent contact distribution epidemic for any given dynamic population epidemic is provided, enabling comparisons to be made for the velocities and final outcomes displayed by the two classes of models. The relationship between deterministic and stochastic epidemic models is also discussed briefly.

Disease Outbreaks↗
PubMed1995

Preattentive equivalence of multicomponent Gabor textures in the central and peripheral visual field.

Similarity ratings were obtained to determine the minimum number of Gabor components that would produce a comparison texture that appeared preattentively similar to a 64-component standard texture. All textures were chosen to be both specifiable by a relatively small number of localized spectral components and sufficiently complex to approximate natural textures. The number of component orientations in the set of comparison textures was found to be a particularly important determinant of texture discrimination in that its effect on rated similarity was largely independent of the total number of components making up the texture. Textures were also presented at 0.75 degree and 20 degrees eccentricity, with the latter magnified by a factor of either 2 or 4. The overall similarity rating did not change with either magnification, whereas the critical number of orientations, defined as the number of orientations above which rated similarity was constant, did change for the higher magnification. The latter finding is consistent with the proposition that higher-order discriminations are mediated by higher cortical areas that integrate information across the visual field. Finally, the phase-bandwidth of a set of coherent textures was also varied in order to determine whether more explicit differences in the spatial structure of stimuli might affect rated similarity. In contrast to the results for component orientation, the ratings, obtained at 0.75 degree and 20 degrees, were different even when the phase-bandwidth stimuli were magnified by a factor of 4.

Adult↗
PubMed1994

Detection and direction discrimination performance with flicker gratings in peripheral vision.

Detection and direction discrimination experiments were conducted with luminance and flicker gratings. The flicker gratings had bars made up of static random pixels interspersed between other bars with flickering random pixels. All experiments were carried out in peripheral vision with grating images centered at 8 deg eccentricity in the superior retina. Detection of flicker gratings (i) was independent of pixel size, (ii) declined with spatial frequency in the range 1-4 c/deg, and (iii) improved with stimulus area (number of grating cycles). Detection performance with a flicker grating was comparable to that obtained with a low-contrast (0.01) luminance grating, and the results suggest that the spatial structure of a flicker-domain stimulus is based upon signals which are weak compared to the maximum signals attainable with a luminance-domain stimulus. With the detectability of flicker and luminance gratings equated, d' for discriminating the direction of motion of a luminance grating increased with step size (1/12 to 1/4 cycle) whereas direction discrimination performance with a flicker grating remained unchanged and at chance levels. Under the conditions tested, there was no evidence that the motion of a flicker-domain stimulus could be processed peripherally. Constraints on alternative models of motion processing are discussed.

Contrast Sensitivity↗