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PubMed1992

Shape distributions of protein topography.

A method is presented for measuring protein surface shape. It is an improvement of an earlier method that intersects a sphere with the solvent-excluded volume of a protein molecule. The new method, called a shape distribution, produces a more sophisticated description of the region of the sphere inside the protein than is provided by simply measuring the region's area or solid angle. This method is applied to the prediction of molecular complexes in three systems: the hemoglobin nonallosteric interface, trypsin and trypsin inhibitor, and heme and apomyoglobin. It does not uniquely predict the correct structure, even though the individual structures are taken from the experimentally determined complex structure. However, it does provide a list of several hundred predicted complexes, one of which is correct, and from which the correct complex might be extracted by a subsequent chemical filter.

Algorithms↗

PubMed1990

[Dental sac and its role in periodontal development].

The present study examined the role of the innermost layer of dental sac tissue in periodontal development. Empty bony crypts were filled with Hydroxylapatite ceramic granules of porous consistency in 5-day-old rats. After 4.5 and 24 weeks the specimens were processed for light and transmission electron microscopy. Only 4 weeks later cement regeneration was seen on ceramic surfaces with bundles of oriented collagen fibers inserting in the cementoid matrix. Ultrastructurally the newly formed cementum-like tissue was in intimate contact to the synthetic hydroxylapatite crystals. A consistent finding was the presence of an interface between cementum and the ceramic surface. The present findings question the unique role of the "investing layer" in periodontal development and the existence of cement-inducting properties of dentin.

Animals↗

PubMedDate not supplied

Liquid chromatographic-atomic absorption spectrophotometric method for determination of methyl mercury in seafood: collaborative study.

A previously developed method that uses a simplified sample preparation procedure and atomic absorption detection of liquid chromatographic eluates for the determination of methyl mercury in seafood has been collaboratively studied. The unique feature of the method involves the use of a specially designed interface for the generation of mercury vapor. Methyl mercury is isolated from the blended sample by chloroform elution from a diatomaceous earth-hydrochloric acid column. The organomercury compound is then extracted into a small volume of 0.01M sodium thiosulfate solution. An aliquot of this solution is injected onto a Zorbax ODS column and eluted with methanol-ammonium acetate solution (3 + 2), pH 5.7, containing 0.01% mercaptoethanol. Mercury is detected by flameless atomic absorption spectrophotometry using the interface. The samples analyzed in the study were unspiked swordfish, unspiked and spiked lobster, and unspiked and spiked tuna. The spiked samples contained methyl mercury both above and below the U.S. Food and Drug Administration guideline level of 1 microgram Hg/g. Reproducibility relative standard deviations ranged from 10.5% at 1 microgram Hg/g to 18.2% at about 0.1 microgram Hg/g. Accuracy, measured by comparison to reference values obtained by the Associate Referee, ranged from 94.4 to 99.6%. The method has been adopted official first action.

Animals↗

PubMed1990

Magnetic resonance imaging simulator: a teaching tool for radiology.

The increasing use of magnetic resonance imaging (MRI) as a clinical modality has put an enormous burden on medical institutions to cost effectively teach MRI scanning techniques to technologists and physicians. Since MRI scanner time is a scarce resource, it would be ideal if the teaching could be effectively performed off-line. In order to meet this goal, the radiology Department at the University of Pennsylvania has designed and developed a Magnetic Resonance Imaging Simulator. The simulator in its current implementation mimics the General Electric Signa (General Electric Magnetic Resonance Imaging System, Milwaukee, WI) scanner's user interface for image acquisition. The design is general enough to be applied to other MRI scanners. One unique feature of the simulator is its incorporation of an image-synthesis module that permits the user to derive images for any arbitrary combination of pulsing parameters for spin-echo, gradient-echo, and inversion recovery pulse sequences. These images are computed in 5 seconds. The development platform chosen is a standard Apple Macintosh II (Apple Computer, Inc, Cupertino, CA) computer with no specialized hardware peripherals. The user interface is implemented in HyperCard (Apple Computer Inc, Cupertino, CA). All other software development including synthesis and display functions are implemented under the Macintosh Programmer's Workshop 'C' environment. The scan parameters, demographics, and images are tracked using an Oracle (Oracle Corp, Redwood Shores, CA) data base. Images are currently stored on magnetic disk but could be stored on optical media with minimal effort.

Computer Simulation↗

PubMed1989

Ordered disruption of subunit interfaces during the stepwise reversible dissociation of Escherichia coli phosphofructokinase with KSCN.

The reversible inactivation and dissociation of the allosteric phosphofructokinase from Escherichia coli has been studied in relatively mild conditions, i.e., in the presence of the chaotropic agent KSCN. At moderate KSCN concentration, the loss of enzymatic activity involves two separated phases: first, a rapid dissociation of part of the tetramer into dimers, second, a slower displacement of the dimer-tetramer equilibrium upon further dissociation of the dimer into monomers. These two reactions can no longer be distinguished above 0.3 M KSCN since complete inactivation occurs in a single reaction. Different changes are observed for the fluorescence and the activity of the enzyme in KSCN: the fluorescence is not affected by the dissociation into dimers which is responsible for inactivation. The decrease in fluorescence reflects the change in environment of the unique tryptophan residue, Trp 311, during the dimer to monomer dissociation. This residue belongs to the interface containing the regulatory site, and its native fluorescence indicates that this interface is still present in the dimer. The substrate fructose 6-phosphate protects phosphofructokinase from inactivation by binding to the tetramer and prevents its dissociation into dimers. The presence of phosphoenolpyruvate prevents the slow dissociation of the dimer into monomers, which shows the ability of the dimer to bind the inhibitor. Two successive processes can be observed during reassociation of the protein upon KSCN dilution. First, a fast reaction (k1 = 2 x 10(5) M-1.s-1) is accompanied by a fluorescence increase and results in the formation of the dimeric species.(ABSTRACT TRUNCATED AT 250 WORDS)

Allosteric Regulation↗

PubMed1988

Endothelial communication. State of the art lecture.

By virtue of its location at the interface of flowing blood and vascular tissue, the endothelial cell monolayer is in a unique position for interactions with soluble and cellular elements of the blood on one side and with component cells of the vascular tissue on the other. This brief review outlines humoral and contact-mediated endothelial communication with other cells, particularly the resident cells of the vessel wall. Evidence for gap junctional communication channels between endothelium and vascular cells is summarized and discussed in relation to endothelial ion channel activity. Myoendothelial gap junctional communication is proposed as a mechanism involved in vasorelaxation, either independent of or in concert with secreted endothelium-derived relaxing factor(s).

Acetylcholine↗

PubMed1987

Neuropeptide Y, somatostatin, and reduced nicotinamide adenine dinucleotide phosphate diaphorase in the human striatum: a combined immunocytochemical and enzyme histochemical study.

Neuropeptide Y and somatostatin immunoreactive neurons and processes were examined in human striatum using both immunofluorescence and avidin biotin immunoperoxidase methods. Reduced nicotinamide adenine dinucleotide phosphate diaphorase activity was histochemically determined by the reduction of nitro blue tetrazolium. Immunofluorescence using a monoclonal anti-somatostatin antibody and a polyclonal anti-neuropeptide Y antibody, followed by diaphorase histochemistry, showed that these three neurochemical markers are co-localized in a single population of medium-sized aspiny intrinsic neurons. Cells were evenly distributed in clusters throughout the striatum, but fiber density was higher in the nucleus accumbens and ventromedial regions of the caudate and putamen. Double-stained reduced nicotinamide adenine dinucleotide phosphate diaphorase-acetylcholinesterase sections demonstrated that these neurons are located in zones of high acetylcholinesterase activity, often at the interface of these zones with regions of low enzyme activity. These biochemically distinctive neurons are uniquely situated to modulate activity between striatal compartments. Our findings provide new information about the modular organization of the striatum and extend these observations in human brain.

Aged↗

PubMed1992

The major piscine liver alcohol dehydrogenase has class-mixed properties in relation to mammalian alcohol dehydrogenases of classes I and III.

The major alcohol dehydrogenase of cod liver has been purified, enzymatically characterized, and structurally analyzed in order to establish original functions and relationships among the deviating classes of the enzyme in mammalian tissues. Interestingly, the cod enzyme exhibits mixed properties--many positional identities with a class III protein, but functionally a class I enzyme--blurring the distinction among the classes of alcohol dehydrogenase. The two domain interfaces, affected by movements upon coenzyme binding, both exhibit substitutions in a manner thus far unique to the cod enzyme. In contrast, coenzyme-binding residues are highly conserved. At the active site, inner and outer parts of the substrate pocket show different extents of amino acid replacement. In total, no less than 7-10 residues of 11 in the substrate binding pocket differ from those of all the mammalian classes, explaining the substrate specificities. However, the inner part of the substrate pocket is very similar to that of the class I enzymes, which is compatible with the observed characteristics of the cod enzyme: ethanol is an excellent substrate (Km = 1.2 mM) and 4-methylpyrazole is a strong inhibitor (Ki = 0.1 microM). These values are about as low as those typical for the ethanol-active class I mammalian enzyme and do not at all resemble those for class III, for which ethanol is hardly a substrate and pyrazole is hardly an inhibitor. Further out in the substrate pocket, several residues differ from the mammalian classes, affecting large substrates.(ABSTRACT TRUNCATED AT 250 WORDS)

Alcohol Dehydrogenase↗

PubMed1978

Interactive computer surface graphics approach to study of the active site of bovine trypsin.

A descriptive medium for the presentation of protein structure has been developed and used to evaluate the structure of the active site of bovine trypsin (EC 3.4.21.4). This technique, involving advanced computer graphics technology, permits the facile display of a representation of the molecular surface of proteins of known structure and employs color to code the structural or chemical features of this surface. Benzamidine derivatives were inserted into the benzamidine-binding site of trypsin and the binary inhibitor-trypsin complex was evaluated by using the computer-generated structure. On the basis of qualitative assessments of the contribution of electrostatic and hydrophobic forces to the binding energy associated with complex formation, we made predictions concerning the effects of interaction of benzamidine substituents and amino acid side chains upon the binding energy associated with inhibitor-protein binding. The computer display of the molecular surfaces of the binary complex of substituted benzamidines and trypsin permitted unique insight into the identity and chemical properties of the atoms that participate at the interface of the molecular surfaces of the inhibitor and the protein. The computer-generated molecular surface display can potentially be combined with quantitative definition of the physical forces involved in the interaction of molecular surfaces. This technology should facilitate the study of the structure-activity relationship of substrates, inhibitors, and drugs that bind to proteins of known three-dimensional structure.

Animals↗

PubMed1992

A graphical user interface for quantitative imaging and analysis of electrophoretic gels and autoradiograms.

DNA/GUI (DNA Graphical User Interface) is an interactive software system for rapid and efficient analysis of images of the types used in genome mapping, such as autoradiograms and electrophoretic gels. Images are digitized using a commercially available charge-coupled-device (CCD) camera system and analyzed on a graphics workstation using a menu-driven user interface. DNA/GUI features automatic lane and band detection, simultaneous display of multiple images and a unique spatial-normalization algorithm. Images and their associated data are archived and easily available for later recall. Preliminary results indicate that DNA/GUI is a useful tool in the analysis and comparison of images used in a variety of applications such as genetic-linkage analysis and DNA restriction mapping. The interactive display software is based on the X Window System and is therefore readily portable to a variety of graphics workstations.

Autoradiography↗

PubMed1991

Air interface and elastic recoil affect vascular resistance in three zones of rabbit lungs.

We examined the effect of the air interface on pulmonary vascular resistance (PVR) in zones 1, 2, and 3 by comparing pressure-flow data of air- and liquid-filled isolated rabbit lungs. Lungs were perfused with Tyrode's solution osmotically balanced with 1% albumin and 4% dextran and containing the vasodilator papaverine (0.05 mg/ml). Lung volume was varied by negative pleural pressure form 0 to -25 cmH2O. Pulmonary artery (Ppa) and venous (Ppv) pressures were fixed at various levels relative to the lung base. Alveolar pressure (PA) was always zero, and perfusate flow was measured continuously. In zone 1 Ppa was -2.5 cmH2O and Ppv was -15 cmH2O. In zone 2 Ppa was 10 cmH2O and Ppv was -5 cmH2O. In zone 3 Ppa was 15 cmH2O and Ppv was 8 cmH2O. We found that in zone 1 the interface was essential for perfusion, but in zones 2 and 3 it had much lesser effects. In general, PVR depended almost uniquely (i.e., with small hysteresis) on transpulmonary pressure, whereas a large hysteresis existed between PVR and lung volume. PVR was high in collapsed and especially in atelectatic lungs, fell sharply with moderate inflation, and within the ranges of vascular pressure studied did not rise again toward total lung capacity. These results suggest that in zone 1 the interface maintains the patency of some alveolar vessels, probably in corners. The majority of alveolar septal vessels appears to be exposed directly to PA in zones 2 and 3, because at equal transpulmonary pressure the PVR is similar in the presence or absence of an interface.

Air↗

PubMed1992

A case of pigmentary type of orthochromatic leukodystrophy with early onset and globoid cells.

We report herein a sporadic case of the pigmentary type of orthochromatic leukodystrophy with early onset and very rapid clinical course. The patient's development was normal until 2 years old, when he experienced visual disturbance. Rapid deterioration resulted in death 1.5 years after the onset. Metachromatic leukodystrophy, globoid cell leukodystrophy and adrenoleukodystrophy were excluded by biochemical assays. Autopsy findings were compatible with the diagnosis of the pigmentary type of orthochromatic leukodystrophy. However, there were unique findings of severe neuronal loss and the collection of globoid-like cells in the interface of the gray matter and the white matter. Immunohistochemical staining of myelin basic protein, proteolipid protein and galactocerebroside demonstrated that these myelin constituents were equally preserved in the posterior column, while absent in the lateral and anterior columns of the spinal cord.

Autopsy↗

PubMed1976

Issues at the clinical-research interface: placebo effect control groups.

At the clinical-research interface, controls are a significant issue in group therapy evaluation. The authors describe and analyze their unique experience with placebo effect control groups conducted prior to brief, group psychotherapy for married couples. Procedures are outlined and participant reactions noted. Solicited ratings and spontaneous comments provide assessment data. The evidence suggests the feasibility of placebo effect control groups in the context studied. Proposed methodological refinements and clinical implications may be useful for future research efforts.

Adult↗

PubMed1992

The evolution of neural circuits controlling feeding behavior in frogs.

Our approach to understanding motor systems is a phylogenetic, 'outside-in' approach, the goal of which is to identify behavioral transitions during phylogenesis and elucidate their neurological basis. In this paper, we review the results of recent behavioral, biomechanical and neurological studies on frog feeding behavior. These studies show that highly protrusible tongues have evolved numerous times independently among frogs, and that the biomechanics and neuromuscular control of feeding behavior have been transformed repeatedly during frog evolution. Many of the independent lineages possess unique biomechanical mechanisms for protracting their tongues and unique neural mechanisms for coordinating feeding behavior. In frogs, there has been considerable evolution at the interface between reticular central pattern generators (CPGs) associated with feeding and sensory feedback circuits that modulate feeding motor output. In particular, the roles of hypoglossal and glossopharyngeal sensory feedback appear to have been relatively plastic in their evolution. Prey-type dependence of hypoglossal sensory feedback in Rana suggests that the interaction between descending visual control and sensory feedback also may be evolutionarily plastic. Comparative studies have found that motor systems sometimes evolve conservatively across morphological and behavioral transitions (i.e., the shoulder in birds) or, alternatively, they may be subject to considerably more evolutionary change than is reflected in morphological characteristics (i.e., feeding in cichlids). We hypothesize that the CPG circuits for feeding behavior in the reticular formation may evolve conservatively because they are highly integrated, multifunctional networks which cannot be optimized for one function without compromising others. In contrast, the interfaces between the CPG, sensory feedback and descending control should be less constrained. When changes in motor patterns occur during evolution, it is likely that sensory feedback or descending control may be involved.

Animals↗

PubMed1977

Environment and the skin.

The skin is an important interface between man and his environment; it is an important portal of entry for hazardous agents and a vulnerable target tissue as well. It is a uniquely accessible model system for detecting hazards and for studying mechanisms of a wide variety of biologic funcitons. Environmental causes of skin reactions comprise a vast array of physical, chemical and biological agents. To appreciate the role of the skin as an interface with man's environment, it is necessary to understand the multiple adaptive mechanisms, and the defenses of the skin against the environmental stresses. The skin is endowed with a versatile group of defenses against penetration, fluid loss from the body, thermal stress, solar radiation, physical trauma and microbial agents. Patterns of adverse response range in quality and intensity from uncomplicated itching to metastatic neoplasia. Environmental problems comprise a large segment of disabling skin disease. Although critical epidemiologic data is limited, cutaneous illnesses comprise a significant segment of occupational disease. This represents a significant loss in productivity and a major cause of disability. The most serious research needs include the development of surveillance systems for identifying skin hazards and determining frequency of environmental skin disease; the development of new models for studying cutaneous penetration; the elucidation of the mechanisms of nonallergic inflammatory reactions (primary irritation) and of the accommodation phenomenon; the development of more sensitive models for predicting adverse responses to marginal irritants; the utilization of modern skills of immunobiology and immunochemistry to elucidate mechanisms of allergic responses; the launching of epidemiologic studies to determine the long term effects of PCBs and associated compounds such as dioxins; and the expansion of research in the mechanisms of skin cancer in relation to susceptibility, genetic and metabolic considerations, ultraviolet light, and phototoxic agents.

Dermatitis, Contact↗

PubMed1990

A novel mechanism of heme-heme interaction in the homodimeric hemoglobin from Scapharca inaequivalvis as manifested upon cleavage of the proximal Fe-N epsilon bond at low pH.

The CO-binding kinetics and the optical spectra of the NO derivative of the homodimeric hemoglobin from Scapharca inaequivalvis have been investigated over the range between pH 7.0 and 2.0. In the deoxygenated derivative, protonation of the proximal imidazole at very low pH values and the consequent cleavage of the Fe-N epsilon bond result in a approximately 50-fold enhancement of the rate constant for CO binding, as found in other hemoproteins. However, in the case of the hemoglobin from S. inaequivalvis, the pH profile displays a cooperative behavior (n = 1.8 +/- 0.1), a unique feature that differentiates this protein from any other hemoprotein investigated thus far. Cleavage of the proximal bond in the NO derivative of S. inaequivalvis hemoglobin likewise displays a very steep pH transition. The mode of assembly of the homodimer, in which the heme-carrying E and F helices provide the subunit interface and bring the hemes at a much shorter distance (18.4 A) than in vertebrate hemoglobins, is likely to provide the structural basis for this unique behavior.

Animals↗

PubMed1989

Intermediates on the reassociation pathway of phosphofructokinase I from Escherichia coli.

The folding and association pathway of the allosteric phosphofructokinase from Escherichia coli has been investigated after complete denaturation of the protein in guanidine hydrochloride by spectroscopical methods, fluorescence and circular dichroism. Three successive processes can be observed during the renaturation of this protein. First, a fast reaction, detected by fluorescence, results in the formation of a (partially) structured monomer. Second, two monomers associate into a dimeric species. This step involves the shielding of the unique tryptophan residue, Trp 311, from the aqueous solvent, and it corresponds to the formation of the interface containing the effector binding site. The presence of ATP during renaturation increases the rate of formation of this dimeric species. The other ligands of the enzyme have no effect on this reaction as well as on the whole reactivation. Finally, the enzymatic activity is regained during the third slowest step. This last reaction is due to the association of two dimers into the native tetrameric structure. The presence of fructose 6-phosphate does not increase the rate of reactivation, even though this ligand strongly stabilizes the native enzyme against denaturation by bridging the interface corresponding to the active site. The self-assembly of phosphofructokinase from E. coli from its unfolded and separated chains follows a specific order in the formation of the interactions between subunits and involves a dimeric intermediate with a defined geometry.

Allosteric Regulation↗

PubMed1991

Counselling at the cultural interface: is getting back to roots enough?

This paper attempts to view counselling in its cultural context. The central issue addressed relates to the possibly unique position which psychiatric nurses occupy in relation to this issue. It is argued that psychiatric nurses have an opportunity to challenge some of the complexities and assumptions of traditional counselling models, and contribute towards the development of a helping approach, for those who are culturally 'different', which is both authentic and flexible. After tracing the notion of cultural identity and outlining the disempowering experience of many from the cultural minority groups, when encountering the British psychiatric system, the writer considers the relevance of the Western counselling tradition in relation to those who are thus disempowered. Viewed from the complexity of human experience and cultural variability, it is claimed that many of the assumptions and premises of this tradition are themselves disempowering. An argument is made for that kind of authentic helping whose genesis is the recognition of clients in their cultural setting and which is flexible enough to respond to the individual and not merely her/his cultural grouping. With such a framework, the writer feels that psychiatric nurses could occupy a vital role, whose goal would be to re-empower individuals with diverse cultural traditions, at both a micro and macro level.

Attitude to Health↗