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At least 1,693 records · Page 94Linked to original sources
PubMed1993

[Conformation of fragment 66-72 of interleukin-2 complexed with a monoclonal antibody to interleukin-2].

1H-NMR spectra of the interleukin-2 synthetic fragment Ac-Leu66-Glu-Glu-Val-Leu-Asn-Leu72-OCH3 in the presence or absence of the monoclonal antibody were analysed. The data obtained are consistent with an extended unordered conformation of the free peptide. Measurements of NOESY cross-peak intensities allowed us to determine the spatial structure of the peptide bound to the antibody. The peptide has an amphiphilic surface with hydrophobic and hydrophilic amino acid side chains clustered on the opposite sides of its alpha-helical-like structure. The hydrophobic and hydrophilic clusters are located on the opposite sides of the bound peptide's surface. The hydrophobic side chains contact the antibody surface, while the hydrophilic ones are oriented into the solvent (T. A. Balashova et al. (1991) Bioorgan. Khim. (USSR), v. 17, p. 1470-1486). Hydrolysis of the methyl ester slowly ocurs in the presence of the antibody. This process does not alter the conformation of the peptide bounded with the antibody, though decreases the peptide's affinity to the antibody.

Amino Acid Sequence↗
PubMed1995

Different uses of chromatic signals in patients with congenital and acquired colour vision deficiencies.

Chromatic signals can be used to generate perceived colour and also to detect spatially structured objects defined only by chromatic differences. These two attributes have previously been investigated in dichromats and cerebral achromatopsic patients using a new colour vision test developed at City University that makes possible the isolation of pure chromatic signals (Barbur et al. Proc. R. Soc. London B 258, 327-334, 1994). We have investigated acquired colour vision changes in a 69-year-old patient, after conventional colour vision tests gave ambiguous results. His ability to detect an object using chromatic signals was impaired more than his ability to detect a colour change, and this impairment was greater in the right eye than in the left eye. This dissociation suggests parallel pathways may be involved in the two processes of coding chromatic signals. Recent neurological testing on the same patient has indicated the onset of multiple sclerosis. Our much earlier finding based on colour vision testing may therefore have useful diagnostic implications.

Aged↗
PubMed1995

[Conformational state of oncoprecipitin cyprein and its immunologic activity].

The effect of solution ionic strength, calcium ion concentration, and temperature on spatial structure of cyprein was examined by CD, UV, and fluorescence spectroscopy. The secondary structure of the cyprein molecule was calculated from CD spectra, and the prevalence of the beta-structure (85%) was shown. An irreversible conformational transition in the range 55-60 degrees C was found, which reduces the binding activity of cyprein in interaction with carcinoembryonic antigen (CEA) and anti-cyprein antibodies. In the latter case, the binding activity was reversibly restored. Cyprein was shown to be a calcium-binding protein. Binding of calcium by cyprein and increasing the ionic strength of solution affect only tertiary structure of the protein. At an ionic strength of solution close to physiological conditions, calcium-bound cyprein shows maximum binding to CEA and anti-cyprein antibodies. It was shown by difference UV spectroscopy that cyprein does not interact specifically with the monosaccharides of the carbohydrate chains of CEA: fucose, mannose, galactose, and N-acetylglucosamine.

Calcium↗
PubMed1996

Development of pupillary responses to grating stimuli.

Pupillary responses to stationary, achromatic sine wave gratings were measured in adults and in 1- and 3-month-old infants. Measurements of behaviourally determined contrast sensitivity were also obtained from the infant subjects. Contrast sensitivity functions were typical of those previously described: band-pass in nature with sensitivity increasing markedly with age. The pupil grating response amplitudes also exhibited a spatial frequency and age dependence similar to that observed for contrast sensitivity. These findings provide further evidence that the neural mechanisms which underlie visual sensitivity to contrast also mediate pupillary responses to spatial structure.

Adult↗
PubMed1996

[Human tumor necrosis factor mutants: preparation and some properties].

Using polymerase chain reaction, a number of mutant genes encoding human tumor necrosis factor (TNF-alpha) with amino acid substitutions and a deletion were obtained. The mutant proteins (muteins) contained point mutations R32H, A33S, F144L, I118M, and I118A; double mutation R32H-F144L; and deletion of four amino acid residues 67-70. The mutant genes were expressed in E. coli under the control of constitutive promoters. A simple purification method for the muteins was developed and their physicochemical properties were studied. All the muteins obtained, except F144L and I118A, were shown by CD and cross-linking to from a spatial structure similar to that of the native TNF-alpha. The collection of muteins was characterized by their biological activity. Mutants R32H and A33S exerted a decreased cytotoxicity against murine fibroblast cell line L929, whereas point mutant F144L and double mutant R32H-F144L were essentially inactive.

Base Sequence↗
PubMed1996

Comparison of magnetic resonance imaging and Laser Doppler Anemometry velocity measurements downstream of replacement heart valves: implications for in vivo assessment of prosthetic valve function.

BACKGROUND AND AIM OF THE STUDY: The non-invasive, in-vivo assessment of prosthetic valve function is compromised by the lack of accurate measurements of the transvalvular flow fields or hemodynamics by current techniques. Short echo time magnetic resonance imaging (MRI) may provide a method for the non-invasive, in vivo assessment of prosthetic valve function by accurately measuring changes in the transvalvular flow fields associated with normal and dysfunctional prosthetic valves. The objectives of these in vitro experiments were to investigate the potential for using MRI as a tool to measure the complex flow fields distal to replacement heart valves, and to assess the accuracy of MRI velocity measurements by comparison with Laser Doppler Anemometry (LDA), a gold standard. METHODS: The velocity fields downstream of tilting disc, bileaflet, ball and cage, and pericardial tissue valves were measured using both three-component LDA and MRI phase velocity encoding under a steady flow rate of 22.8 l/min, simulating peak systolic flow. The valves were tested under normal and stenotic conditions to assess the MRI capabilities under a wide range of local flow conditions, velocities and turbulence levels. A new short echo time MRI technique (FAcE), which allowed velocity measurements in stenotic jets with high turbulence, was tested. RESULTS: Good overall agreement was obtained between the MRI velocity measurements and the LDA data. The MRI velocity measurements adequately reproduced the spatial structure of the flow fields. In most cases peak velocities were accurately measured to within 15%. CONCLUSIONS: The results indicate that the FAcE MRI method has the potential to be used as a diagnostic tool to assess prosthetic valve function.

Aortic Valve↗
PubMed1996

An in vitro investigation of the retrograde flow fields of two bileaflet mechanical heart valves.

BACKGROUND AND AIM OF THE STUDY: Fluid stresses occurring in retrograde flow fields during valve closure may play a significant role in thrombogenesis. The squeeze flow and regurgitant jets can cause damage to formed blood elements due to high levels of turbulent shear stress. The aim of this study was to characterize in detail the spatial structure and temporal behavior of the retrograde flow fields of the St. Jude Medical and Medtronic Parallel bileaflet mechanical heart valves. METHODS: Three-component, coincident laser Doppler anemometry (LDA) velocity measurements were obtained facilitating the determination of the full Reynolds stress tensor and the principal stresses in the valve flow fields. The experiments were performed in the Georgia Tech aortic flow chamber under physiologic pulsatile flow conditions. Data were collected over several hundred cardiac cycles for subsequent phase window averaging and generation of mean velocity and turbulence statistics over 20 ms intervals. A region approximately 8 mm x 10 mm was mapped 1.0 mm upstream of one hinge of each valve with an incremental resolution of 0.13-0.25 mm. Animation of the data allowed the visualization of the flow fields and a quantitative display of mean velocity and turbulent stress values. RESULTS: In the St. Jude Medical squeeze flow, the peak turbulent shear stress was 800 dynes/cm2 and the peak reverse velocity was 0.60 m/s. In the Medtronic Parallel squeeze flow, the peak turbulent shear stress was 1,000 dynes/cm2 and the peak velocity 0.70 m/s. The leakage jet fields of the two valves were very different: in the case of the St. Jude Medical valve, turbulent shear stresses reached 1,800 dynes/cm2 and peak jet velocity was 0.80 m/s; in the case of the Medtronic Parallel valve, turbulent shear stresses reached 3,690 dynes/cm2 and the peak jet velocity was 1.9 m/s. CONCLUSIONS: The retrograde flow fields of these two bileaflet mechanical heart valves appear to be design-dependent. The elevated turbulent shear stresses generated by both valve designs may indicate a propensity for blood element damage during the reverse flow phase of the cardiac cycle, but the extent of flow disturbance was twice as high with the Medtronic Parallel than with the St. Jude Medical valve. This research should yield a better understanding of the significance of retrograde flow to the functionality and potential thrombogenicity of bileaflet mechanical heart valves and aid in the development of new designs.

Heart Valve Prosthesis↗
PubMed1996

[Biological, behavioral and intellectual rhythms in pupils during the school-day].

We report in this paper the data separately collected for 15 years by the research teams of Montagner and Testu on the daily fluctuations of the periodical type and ultradian and circadian rhythms of biological, behavioural and mental variables which are or could be linked to or correlated with the fluctuations of intellectual activity in pupils throughout the school-day. The variables under study are the behaviours which are considered to be indicators of vigilance and non vigilance (arousal and drowsiness), corporal activation, heart rate, blood pressure, performances in tests of vigilance, targeted attention, spatial structuration and logical construction, and also in usual school tasks. Studies were carried out on different children populations at all ages (in this article we only report data on children attending primary school and partly kindergarten) in different French schools and, with regard to Testu's studies, several european schools in England, Germany and Spain. The main data collected by both teams are comparable in many respects: 1) the vigilance level and intellectual performances of pupils of all ages are weak or relatively weak at the beginning of the school activities, i.e. from 8 to 9 or 9:30 according to the studies and measured variables, as the biological constraints are not at a high level (heart rate and blood pressure); 2) the same items or patterns significantly increase throughout school time up to 11:30 or noon according to the studies with the exception of the 11:00-11:30 span in Montagner's research in children attending the first level of primary school, as the biological constraints decrease; 3) in most studies the vigilance level and intellectual performances are weak or relatively weak at the beginning of the school-time following the lunch, and the biological constraints are the strongest of the day (from 13:30 to 15:00) ; 4) the vigilance level and intellectual performances are always higher in the middle of the school-day (i.e. from 15:00 to 17:00) than at the beginning of the afternoon, and the biological constraints are weaker.

Adolescent↗
PubMed1996

[Imaging methods in traumatology of the shoulder- and elbow joint].

Radiological diagnostics (diagnostic imaging) of the traumatised shoulder and elbow joint has expanded considerably and has become increasingly meaningful in recent years. The introduction of computed tomography and magnetic resonance imaging has enabled a significantly better assessment of soft parts and of the inner spatial structure of the joints. Hence, focus of diagnosis has now shifted from the assessment of the bones (which was previously the main aspect of diagnosis) to a different analysis of the joint as a functional unit of bone and soft part structures, an analysis that can also detect subtle changes such as additive micro-traumas. The article reviews the conventional imaging methods and the present state of the art in tomographic imaging technique, and illustrates this by means of several representative examples of diagnostic imaging.

Elbow Joint↗
PubMed1996

[Conformation properties of heme-containing proteins using spin labels].

The review briefly summarizes the results of spin-label studies of conformational transitions in monomeric globins (myoglobin, leghemoglobin, erythrocruorin) as well as in another heme-containing protein, cytochrome c, induced by heme ligands and pH. In contrast with integral methods of investigation, for proteins with a known spatial structure the use of the spin-labelling technique makes it possible to obtain information on the conformational behaviour of the isolated parts of the protein structure which, alongside with the results obtained by other physico-chemical methods, allows a conclusion on the nature of conformational movements in the protein during its functioning. The experimental results fit well into the model which represents a Mb-like structure as composed of three independent rigid helical fragments: AE(ABCDE), F and GH, whose reciprocal arrangement is controlled by N- and C-terminal salt bridges. Synchronous displacement of the above fragments relative to one another, which is due either to the ligand attachment and structural changes in the heme complex or to disturbances in ionic interactions at the N- and/or C-end(s) of the structure under effect of pH or allosteric effectors, might serve as a structural basis for homo- and heterotropic regulation in hemoglobin. Similarly, the spin label method allows for tracing and obtaining important information about local conformational events in cytochrome c which in the native protein are associated with a change in pH in the range of 5-13 and are accompanied by the substitution of the heme sixth ligand, Met-80, by Lys-79 (pH 9.3), and then by Tyr-67 (pK 11.1). Local changes in the conformation and dynamic properties of native cytochrome c provide, if necessary, global changes in its structure upon alkaline denaturation. It was found that substitution of the heme protein ligand, Met-80, by the external ligand, cyanide, markedly alters the dynamic properties of the polypeptide chain segment 67-75 adjacent to Met-80.

Hemeproteins↗
PubMed1997

Amount of defocus is not used as an error signal in the control system of accommodation dynamics.

Usually defocus is considered as the error signal in the negative feedback system of accommodation control. However it is difficult to estimate the amount of defocus from the contrast reduction of a retinal image because both defocus and the spatial structure of the target determine the contrast. To investigate whether the accommodation control system can perceive the amount of error signal (defocus) from the contrast reduction of a retinal image, step responses for various amplitudes of stimuli were measured. The traces were analysed using an exponential curve fitting method in which not only time constant, but also final value of the curve, could be estimated from a portion of the exponential curve. The near-to-far (or -intermediate) step responses have a common path and show that the curve initially goes towards a certain position around the dark focus of the subject and is suddenly clipped around the correct focus position. The time constant and the destination of the curve are independent from the stimulus step amplitude (amount of error). This fact suggests that the accommodative control system does not refer to the amount of error signal when error is large, and that the system monitors only whether retinal blur exists or not. When the system judges the retinal image to be no longer blurred during the preprogrammed fast movement, accommodative response is stopped suddenly and the control is transferred to the other mechanism to hold correct focusing.

Accommodation, Ocular↗
PubMed1997

RNA-hydrolyzing antibodies from peripheral blood of patients with lupus erythematosus.

Experiments and hydrolysis of substrates with known spatial structures (such as yeast tRNAPhe, as well as normal and mutant tRNALys from human mitochondria produced by transcription of the appropriate DNA species, that is, RNA genes) were performed to study the ribonuclease activity of antibodies isolated from blood sera of patients with systemic lupus erythematosus (SLE). The antibody preparations contained two types of ribonuclease activities: the first corresponded to the specificity of ribonuclease A and was found during hydrolysis at low salt concentrations, whereas the second was stimulated by Mg2+ and displayed unique specificity toward double-stranded regions of the substrate. The possible use of the antibody preparations as tools for structural studies of conformational differences between RNA molecules was examined. In experiments with unmodified and mutant tRNALys species differing in one base found in the T-loop, we found that hydrolysis with SLE antibodies can detect small local structural changes in RNA under physiological conditions.

Antibodies, Catalytic↗
PubMed1997

Density of states, metastable states, and saddle points exploring the energy landscape of an RNA molecule.

Detailed knowledge of the energy landscape of a biopolymer molecule is a prerequisite for understanding its folding kinetics and its final spatial structure. In the case of RNA we consider the energy landscape defined on the set of all secondary structures that can be formed by a given sequence. We show that the exploration of this energy landscapes is computationally feasible. For this purpose we present a recursive algorithm for computing the complete density of states and discuss its application to tRNA sequences. For shorter sequences a more detailed analysis of the energy surface is possible using a complete list of all secondary structures. In this case we identify metastable states and the saddle points that connect them.

Algorithms↗
PubMed1997

[Possibilities of microtomography of blood cells].

Social reforms and the technological revolution lead to changes in the environment and human habitat, which deteriorate the ecology in the majority of cases. Blood system in general, specifically, the peripheral blood represent one most sensitive system of the body, reflecting the level of adverse exposures and reaction of the organism to these exposures. The interference microtomographer permits measurements of the spatial structure of optically transparent three-dimensional cytological specimens (blood cells). During preliminary studies a model of interference computer-aided microtomographer has been created and a method for treating preparations for processing by this microtomographer developed.

Blood Cells↗
PubMed1996

[Three-dimensional recons-truction of lumbar-sacral canal and its contents: experimental study].

In order to suit the needs of studies in spinal column surgery on three-dimensional spatial structure and morphology of lumbar-sacral canal and the nervous tissue within it, an experimental model was applied by the authors using lumbosacral specimens from two fresh young adult cadavers. Successive 2mm thick CTM screening was carried out from L3 to S2 vertebral bodies with an interval of 1mm. The serial two-dimensional CT photographical pictures so obtained were inputted into a computer and the three-dimensional images were reconstructed through a VIDAS image analysis system. The experimental results indicated that the three-dimensional images of reconstructed vertebral canal and the nervous tissue within it were lifelike. These images could not only reveal their three-dimensional structure and morphology, but also be cut and composed together at any direction and section by turning and transpositioning along X, Y and Z axes. The authors hold that the visual effect expressed by three-dimensional images reconstructed from two-dimensional pictures can play important role in stereomorphologic, biomechanical, and other studies in fields of anatomy, image analysis, and clinical medicine.

Adult↗
PubMed1998

[Protein E 98-113 sequence is a fusion site of tick-borne encephalitis virus with cellular membrane].

The synthetic peptide with the conservative 98-113 sequence of protein E of tick-borne encephalitis virus was studied in order to elucidate its role in the functioning of flaviviruses. The peptide was shown to inhibit the in vitro infection of macrophages with the virus. An antibody that specifically binds this peptide was found among the set of monoclonal antibodies produced against protein E. This antibody was found to prevent penetration of the virus into liposomes. A correlation was found between our results and data on the spatial structure of protein E and its interspecies homology. The protein E 98-113 sequence of the tick-borne encephalitis virus was found to be the fusion site of the viral envelope with a cellular membrane.

Amino Acid Sequence↗
PubMed2024

A genetic atlas for the butterflies of continental Canada and United States.

Multi-locus genetic data for phylogeographic studies is generally limited in geographic and taxonomic scope as most studies only examine a few related species. The strong adoption of DNA barcoding has generated large datasets of mtDNA COI sequences. This work examines the butterfly fauna of Canada and United States based on 13,236 COI barcode records derived from 619 species. It compiles i) geographic maps depicting the spatial distribution of haplotypes, ii) haplotype networks (minimum spanning trees), and iii) standard indices of genetic diversity such as nucleotide diversity (π), haplotype richness (H), and a measure of spatial genetic structure (GST). High intraspecific genetic diversity and marked spatial structure were observed in the northwestern and southern North America, as well as in proximity to mountain chains. While species generally displayed concordance between genetic diversity and spatial structure, some revealed incongruence between these two metrics. Interestingly, most species falling in this category shared their barcode sequences with one at least other species. Aside from revealing large-scale phylogeographic patterns and shedding light on the processes underlying these patterns, this work also exposed cases of potential synonymy and hybridization.

Animals↗
PubMed2001

Spatial population genetic structure in Trillium grandiflorum: the roles of dispersal, mating, history, and selection.

The roles of the various potential ecological and evolutionary causes of spatial population genetic structure (SPGS) cannot in general be inferred from the extant structure alone. However, a stage-specific analysis can provide clues as to the causes of SPGS. We conducted a stage-specific SPGS analysis of a mapped population of about 2000 Trillium grandiflorum (Liliaceae), a long-lived perennial herb. We compared SPGS for juvenile (J), nonreproductive (NR), and reproductive (R) stages. Fisher's exact test showed that genotypes had Hardy-Weinberg frequencies at all loci and stage classes. Allele frequencies did not differ between stages. Bootstrapped 99% confidence intervals (99%CI) indicate that F-statistic values are indistinguishable from zero, (except for a slightly negative FIT for the R stage). Spatial autocorrelation was used to calculate f the average kinship coefficient between individuals within distance intervals. Null hypothesis 99%CIs for f were constructed by repeatedly randomizing genotypic locations. Significant positive fine-scale genetic structure was detected in the R and NR stages, but not in the J stage. This structure was most pronounced in the R stage, and declined by about half in each remaining stage: near-neighbor f = 0.122, 0.065, 0.027, for R, NR, and J, respectively. For R and NR, the near-neighbor f lies outside the null hypothesis 99%CI, indicating kinship at approximately the level of half-sibs and first cousins, respectively. We also simulated the expected SPGS of juveniles post dispersal, based on measured R-stage SPGS, the mating system, and measured pollen and seed dispersal properties. This provides a null hypothesis expectation (as a 99%CI) for the J-stage correlogram, against which to test the likelihood that post-dispersal events have influenced J-stage SPGS. The actual J correlogram lies within the null hypothesis 99%CI for the shortest distance interval and nearly all other distance intervals indicating that the observed low recruitment, random mating and seed dispersal patterns are sufficient to account for the disappearance of SPSG between the R and the J stages. The observed increase in SPGS between J and R stages has two potential explanations: history and local selection. The observed low total allelic diversity is consistent with a past bottleneck: a possible historical explanation. Only a longitudinal stage-specific study of SPGS structure can distinguish between historical events and local selection as causes of increased structure with increasing life history stage.

Genetics, Population↗