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PubMedDate not supplied

Imaging of complex NMR spectra.

The Point Spread Function (PSF) in NMR imaging is the result of both the line broadening due to magnet field inhomogeneity and the intrinsic spectrum of the nucleus at resonance. In the case of proton imaging, the line broadening dominates the small chemical shifts and the spectral lines are not resolved. This is not generally the case with other nuclei having strong chemical shifts and the PSF then has a complex structure. During imaging, the complex PSF is convolved with the spatial distribution of the nucleus at resonance and this leads to halo artifacts which are dependent on the imaging technique employed. The images due to the ensemble of spectral lines can be separated in principle by deconvolution of the data with the PSF before reconstruction. In the special case where the complex PSF is spatially independent, it can be obtained from the Free Induction Decay (FID) data produced in the absence of a spatially encoding gradient field. This technique has been successfully applied to in-vivo imaging of exogenous perfluorocarbon material.

Animals↗
PubMed1992

Drug binding to higher ordered DNA structures: netropsin complexation with a nucleic acid triple helix.

We have used a combination of spectroscopic and calorimetric techniques to characterize how netropsin, a ligand that binds in the minor groove of DNA, influences the properties of a DNA triple helix. Specifically, our data allow us to reach the following conclusions: (i) netropsin binds to the triplex without displacing the major-groove-bound third strand; (ii) netropsin binding to the triplex exhibits a lower saturation binding density (7.0 base triplets per netropsin bound) than netropsin binding to the corresponding duplex (5.5 base pairs per netropsin bound); (iii) the netropsin-free and the netropsin-bound triplexes each melt in two well-resolved transitions, initial conversion of the triplex to the duplex state followed by duplex melting to the component single-stranded states; (iv) netropsin remains bound to DNA as the triplex melts to the duplex state; (v) netropsin binding thermally destabilizes the triplex in equilibrium with duplex equilibrium dramatically, while thermally stabilizing the duplex to single-strand equilibrium; (vi) netropsin binding to the triplex is enthalpically 4 times more favorable (more exothermic) than netropsin binding to the corresponding duplex; (vii) netropsin binding to the triplex decreases the cooperativity of the triplex----duplex melting event. These results demonstrate that occupancy of the minor groove of a triplex by a ligand such as netropsin can exert a profound impact on the properties of the host triplex, particularly with regard to the equilibrium in which the third strand is expelled from the major groove. Thus, our results reveal considerable major groove/minor groove crosstalk. Such knowledge may prove of practical importance by providing an approach for modulating the affinity and specificity of major-groove-binding third strands in triplex-forming protocols designed to target specific duplex domains. Fundamentally, our results provide insights into the crosstalk that can result when ligands bind to the two major receptor sites of duplex DNA--namely, the major and minor grooves.

Calorimetry, Differential Scanning↗
PubMed1983

Solution conformation of asparagine-linked oligosaccharides: alpha(1-6)-linked moiety.

The solution conformation is presented for representatives of each of the major classes of asparaginyl oligosaccharides. In this report the conformation of the alpha(1-6)-linked moiety is described. The conformational properties of these glycopeptides were determined by high-resolution 1H nuclear magnetic resonance in conjunction with potential energy calculations. The NMR parameters that were used in this analysis were chemical shifts and nuclear Overhauser enhancements. Potential energy calculations were used to evaluate the preferred conformers available for the different linkages in glycopeptides and to draw conclusions and to draw conclusions about the behavior in solution of these molecules. For all classes, identical conformations were found for the 6-arm except for the torsional angle, omega, about the C5-C6 bond of the alpha 1-6 linkage. For high mannose and hybrid structures omega was found to be -60 degrees, for bisected biantennary complex structures omega was 180 degrees, and for complex biantennary structures averaging between -60 degrees and 180 degrees occurs.

Asparagine↗
PubMed1997

T-cell receptor structure and TCR complexes.

The first crystal structures of intact T-cell receptors (TCRs) and their complexes with MHC peptide antigens (pMHC) were reported during the past year, along with those of a single-chain TCR Fv fragment and a beta-chain complexed with two different bacterial superantigens. These structures have shown the similarities and differences in the architecture of the antigen-binding regions of TCRs and antibodies, and how the TCR interacts with pMHC ligands as well as with superantigens.

Animals↗
PubMed1979

Complex factorial structure of Ellis' Irrational Beliefs.

Previous research with a newly developed children's scale for measuring Ellis' constructs with regard to irrational beliefs showed that while the scale clearly reflected theoretically predicted developmental trends, the internal consistency reliability of the overall 11-item scale was relatively low (.56). This low internal consistency suggested that the 11 items were in fact heterogeneous and were not measuring a single, univocal, construct. An exploratory factor analysis was performed on the responses of 788 fifth-through thirteenth-grade students. Results of the Alpha factor and analysis clearly indicate that the scale is multifaceted, i.e., comprised of four orthogonal, interpretable factors. Estimates of internal consistency reliabilities for the separate factors, when corrected for length, revealed that each of the new factors was more reliable than the full scale score in this sample. Potential revisions of the scale, as well as cautions for its use in clinical applications on its present form are discussed.

Adolescent↗
PubMed1994

The cuticle of the nematode Caenorhabditis elegans: a complex collagen structure.

The cuticle of the nematode Caenorhabditis elegans forms the barrier between the animal and its environment. In addition to being a protective layer, it is an exoskeleton which is important in maintaining and defining the normal shape of the nematode. The cuticle is an extracellular matrix consisting predominantly of small collagen-like proteins that are extensively crosslinked. Although it also contains other protein and non-protein compounds that undoubtedly play a significant part in its function, the specific role of collagen in cuticle structure and morphology is considered here. The C. elegans genome contains between 50 and 150 collagen genes, most of which are believed to encode cuticular collagens. Mutations that result in cuticular defects and grossly altered body form have been identified in more than 40 genes. Six of these genes are now known to encode cuticular collagens, a finding that confirms the importance of this group of structural proteins to the formation of the cuticle and the role of the cuticle as an exoskeleton in shaping the worm. It is likely that many more of the genes identified by mutations giving altered body form, will be collagen genes. Mutations in the cuticular collagen genes provide a powerful tool for investigating the mechanisms by which this group of proteins interact to form the nematode cuticle.

Amino Acid Sequence↗
PubMed1981

Volume discrimination learning in golden hamsters: effects of the structure of complex rearing cages.

Golden hamsters (Mesocricetus auratus) were reared from birth to adulthood in a spatially diversified situation (EG); their performances were compared with those of other hamsters housed in standard laboratory cages (SG). The task was to discriminate between 2 cubic volumes of different sizes followed by various test situations designed to define the respective parts played by the 3 spatial dimensions during perception. The results show that surfaces of volumes were mainly taken into account by EG subjects whereas width, alone, was used by the SG animals.

Animals↗
PubMed1976

Fine structure of complex ocelli of a cubomedusan, Tamoya bursaria Haeckel.

The retina of the distal and proximal lens-bearing complex ocelli are composed of pigmented sensory cells and long pigmented cells. A ciliary sheath from each sensory cell, together with the processes of long pigmented cells, extends through the vitreous layer as far as the capsule that envelops the lens. Each ciliary sheath has several ballon-like swellings and the ciliary microtubules, arranged in the 9+2 pattern in the proximal part, are markedly disorganized distally in the swollen parts, out of which extends most of the microvilli in the vitreous layer. It is suggested that some of the microvilli may originate in vesicles that are constricted off from the surface of the pigmented sensory cells. Closely packed microvilli run in parallel in short bundles. In addition to characteristic junctions between sensory cells, junctions that are presumably synaptic and, of a new type in coelenterates, are observed between sensory cells and nerve endings.

Animals↗
PubMed1986

The relationship between signal response selectivity and the functional structure of complex retinal neural networks.

In this paper we simulate the simultaneous responses of 45 neurones within a hypothetical retina to a variety of spatio-temporal signals. Our results demonstrate how specific convergent and divergent excitatory and inhibitory connections are sufficient to determine signal response selectivity of specific ganglion cells and so delimit the known types of center-surround receptive fields.

Animals↗
PubMed1987

Mitochondrial plasmid DNAs of broad bean: nucleotide sequences, complex secondary structures, and transcription.

Three circular plasmid DNA molecules of 1704, 1695 and 1476 nucleotide pairs from broad bean mitochondria (mt-plasmids 1-3) have been sequenced. Within a highly homologous segment of mt-plasmid 1 and 2 are found a series of six directly repeated, inverted repeat sequences, separated by unique sequences. Mt-plasmid 3 contains a series of four inverted repeat sequences, unrelated to the inverted repeat sequences of mt-plasmids 1 and 2. Two RNA molecules of about 440 and 320 nucleotides that are complementary to mt-plasmid 2 were detected. Mapping of 5' and 3' termini of these complementary RNA molecules indicated that all transcription from mt-plasmid 2 occurs within a 441 nucleotide region of the molecule. Evidence for transcription of mt-plasmids 1 and 3 was not found.

Base Sequence↗
PubMed1992

Flow patterns of blood cells in the retinal capillaries. Retinal capillary flow patterns.

We present a new technique for retinal blood cell angiography which was used to investigate flow patterns of blood cells in the retinal capillary net of normal cats. Capillary paths were defined to be the path taken by the labelled blood cells from the terminal arteriole to the entry point into a collecting venule. We were able to define two types of capillary paths. The 'simple' paths were minimally coiled and had a high blood cell flux. The 'complex' paths were coiled, structurally complex and had a low blood cell flux in comparison to the simple paths of the same eye. A simultaneous fluorescein angiogram was performed to reveal the complete anatomy of the capillary net in which the functional paths exist. The possibility that such flow patterns exist in the human retina should be considered.

Animals↗
PubMed1991

X-Ray structure of the antibiotic bacitracin A.

Bacitracins are a group of widely used peptide antibiotics. There has been interest in determining the three-dimensional structure of the bacitracins. However, solution studies indicate significant flexibility in their structure and to date native bacitracins have resisted attempts at crystallisation despite considerable efforts over a number of years by several groups. Here we report the first three-dimensional X-ray structure of a bacitracin, complexed to a subtilisin proteinase. X-Ray diffraction data were collected using synchrotron radiation in combination with the Image Plate Scanner system. The complex structure including two enzymes, two bacitracins, 220 water molecules and two Ca2+ ions was refined by restrained least-squares to a crystallographic R factor ( = sigma [[Fo-Fc]]/sigma [Fo]]) of 16.3% at 2.0 A.

Amino Acid Sequence↗