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At least 379 records · Page 21Linked to original sources
PubMed1984

Electronic spectra for nitrosyl(protoporphyrin IX dimethyl ester)iron(II) and its complexes with nitrogenous bases as model systems for nitrosylhemoproteins.

Soret and visible absorption spectra for nitrosyl(protoporphyrin IX dimethyl ester)iron(II) (Fe(PPIXDME)(NO] and its complexes with nitrogenous bases (imidazoles, pyridines, aliphatic amines, and cyclic secondary amines) as model systems for nitrosylhemoproteins have been measured in various solvents. As the solvent polarity increases, the Soret and visible absorption bands for the five-coordinate Fe(PPIXDME) (NO) were shifted to shorter wavelengths. Accompanying the coordination of a nitrogenous base to the vacant axial position of Fe(PPIXDME)(NO), the Soret band becomes sharp and the band maximum is shifted to longer wavelengths. The band positions for the six-coordinate Fe(PPIXDME)(NO)(Base) complex are not sensitive to the pi-bonding ability of the axial ligand trans to NO group. The electronic spectra of five-coordinate Fe(PPIXDME)(NO) and six-coordinate Fe(PPIXDME)(NO)(Base) complexes are interpreted in relation to the structural information. The comparison of the spectra for model systems with those for nitrosylhemoproteins is discussed.

Amines↗
PubMed1980

Barrier characteristics of membrane model systems containing unsaturated phosphatidylethanolamines.

The barrier characteristics of membrane model systems containing unsaturated phosphatidylethanolamines have been investigated. (1) At increasing temperatures 18:1c/18:lc-phosphatidylethanolamine liposomes lose their permeability barrier for K+ as a consequence of the transition from a lamellar to a hexagonal orientation as detected by 31P-NMR and freeze-fracturing electron microscopy. (2) Introduction of 18:1c/18:1c-phosphatidylcholine in the 18:1c/18:1c-phosphatidylethanolamine lipid system stabilizes the bilayer structure and the permeability barrier for K+ and glucose while cholesterol destabilizes. (3) Upon heating of the investigated 18:1c/18:1c-phosphatidylcholine-18:1c/18:1c-phosphatidylethanolamine-(cholesterol) mixtures, structures are formed which give rise to isotropic 31P-NMR signals and which on the basis of freeze-fracture pictures are interpreted as sponge-like structures. Lowering the temperature results in restoration of the barrier function of the lipid structures.

Freeze Fracturing↗
PubMed1985

Historical perspectives on the development of health systems modeling in medical anthropology.

The call for macro health systems models which emerged in medical anthropology in the mid-1970s from the field's most respected thinkers has a deep theoretical history and can also be related to theoretical developments in sociology, clinical medicine and international public health. The trends leading to a recognition of the need for modeling by medical anthropologists have been the source of some of medical anthropology's limitations and weaknesses as well, especially the failure to fulfill the field's promise as a biocultural bridge for the parent discipline.

Anthropology↗
PubMed2005

Epoxidation with an electrocatalytic p-450 model system in an acidic solution.

An electrochemical P-450 model system using meso-tetraphenylporphyrinatomanganese(III) chloride (MnTPP), imidazole and acetic acid was tested in an acetonitrile solution, and epoxide was obtained with a good current efficiency. The results of cyclic voltammetry revealed that acid plays an important role in the second electron transfer.

Catalysis↗
PubMed2004

Formation of heterocyclic aromatic amines in model systems.

Heterocyclic aromatic amines (HAs) are mutagenic and carcinogenic substances that are formed in significant amounts during heating of meat or fish at temperatures of at least 150 degrees C. To investigate the chemistry lying behind the formation of these harmful substances model systems were established. The first aim was to identify the naturally occurring precursors, namely creatinine, amino acids and carbohydrates. Later these model systems were used to develop strategies for a reduction of the content of the heterocyclic aromatic amines and for the evaluation of the reaction mechanisms that lead to the formation of these substances. All these aspects are discussed in this review.

Amines↗
PubMed1987

The kindling effect as a model system of sensitization and arousal.

The purpose of this paper is to examine the relationship between the general processes of arousal and sensitization and the response increment processes at the cellular level, which have been considered as model systems of behavioural plasticity, i.e. the kindling effect and long-term potentiation in hippocampal pathways. From the published literature it appears that kindling and potentiation may be considered as model systems of sensitization and arousal. Moreover, research on these potentiation effects gives support to the hypothesis of specific arousal systems in the brain which mediate learning and memory. It is proposed that a multidisciplinary approach, including data from behavioural neurobiology and from psychophysiological studies, can contribute to better knowledge of the biological basis of learning.

Animals↗
PubMed1999

Accuracy of the tomey topographic modeling system in measuring surface elevations of asymmetric objects.

BACKGROUND: Most studies have assessed the accuracy of videokeratographic systems using spheres, ellipsoids, or toric surfaces. Most human corneas are asymmetric to some degree and many pathological corneas are markedly asymmetric. To date, little work has been done to ascertain the accuracy of videokeratographic systems for measuring the shape of asymmetric objects. PURPOSE: The purpose of this study is to determine the accuracy with which the Tomey Topographic Modeling System can evaluate the topography of asymmetric surfaces. METHODS: Calibrated ellipsoidal test objects were tilted with respect to the videokeratometric axis to create asymmetric test surfaces with known characteristics. RESULTS: Root mean squared error of all the measured surface elevations varied from 0.7 microm to 11.3 microm. Although there was a trend for greater error with the more asymmetric surfaces, the trend was not statistically significant. Accuracy was not dependent on apical radius. Measurement error increased toward the periphery. CONCLUSIONS: For the Tomey Topographic Modeling System, the accuracy in measurement of smooth, asymmetric surfaces is comparable the accuracy in measurement of symmetric surfaces.

Cornea↗
PubMedDate not supplied

Spectroscopic properties of ubiquinones in model systems.

In order to achieve a better elucidation of the physico-chemical properties of ubiquinones (Qs) in natural membranes, we have investigated the UV spectral features of Q-homologs in different model systems. In phospholipid monolamellar vesicles the UV spectra of physiological ubiquinones resemble those in isooctane, whereas in detergent micelles the spectra appear similar to those of the hydrophilic Q1 in water. For short-chain Qs it is possible to describe a linear dependence of the absorption parameters upon the polarity of the media. Long-chain Qs exhibit strong deviations due to aggregation states. In aqueous media a pH dependence of the spectral properties of ubiquinones is also observed. The findings in model systems can provide useful correlations between the spectroscopic properties of ubiquinones, their physico-chemical characteristics in the natural membranes, and rapid spectrophotometric detections of their redox changes.

Chemical Phenomena↗
PubMed1995

The use of time study results in a system model for presenting dental care outcome.

The documentation of dental care outcome and dental clinic efficiency is based on variables for the patient's dental health and on resources in time and costs concerning the dental treatment. The aim of this paper was to measure dental clinic activities using a time study method in relation to a model for a system for presenting dental care outcome, and the dental clinic's output and efficiency. For efficiency reporting of dental care related effects, the documentation should be based on rules for input costs related to dental clinic activities, based on valid country-wide criteria for work times of the dental personnel; dental care economics; and current epidemiological indices. Additional use of results from time studies made it possible to adapt the need of resources in dental care, and to obtain essential information concerning the choice of dental team models. For reporting, a dental health related patient group system, based on the patients' dental health and need of dental treatment, should be used. In the proposed model for a system for presenting dental care, knowledge of patients, and of what services the dental personnel can perform was used.

Adolescent↗
PubMed1996

The conformation of xanthene dyes in the myosin sulfhydryl one binding site. Part I. Methods and model systems.

Derivatives of the fluorescent probes fluorescein and rhodamine specifically and covalently modify the highly reactive thiol (SH1) of myosin subfragment 1 (S1). Both probes develop circular dichroism (CD) upon modification of SH1 at the visible absorption band of the chromophore. A model system of chiral complexing agents (aromatic chiral amines) interacting with fluorescein in solvent develops a CD signal that mimics that produced by S1. The model system suggests that a specific interaction of the probe with an aromatic chiral residue in the SH1 binding pocket induces the CD signal. Several other spectroscopic signals, including absorption and fluorescence intensity and anisotropy, characterize the fluorescein or rhodamine binding to SH1. A coupled dipole method is adapted to interpret these spectroscopic signals in terms of the probe-S1 complex conformation. The computation of the orientation of the principal hydrodynamic frame (PHF) of S1 from its crystallographic alpha-carbon backbone structure permits the known orientation of the probe in the PHF of S1 to further constrain the conformation of the probe-S1 complex. The coupled dipole interpretation of spectroscopic data combined with constraints relating the probe dipole orientation to the PHF of S1 determines the conformation of the probe-S1 complex. The methods developed here are applied to the spectroscopic signals from fluorescein or rhodamine in the SH1 binding site of S1 to obtain an atomic resolution model of the probe-S1 conformation [Ajtai and Burghardt, Biochemistry, 34 (1995) 15943-15952].

Binding Sites↗
PubMedDate not supplied

Antioxidant properties of rimantadine in influenza virus infected mice and in some model systems.

Influenza virus infection is associated with development of oxidative stress in lung and blood plasma, viz. increase of primary and secondary lipid peroxidation products. It was established that rimantadine treatment led to a decrease of the products of lipid peroxidation in tissues of mice experimentally infected with influenza virus A/Aichi/2/68 (H3N2). The effect is strongest in blood plasma (a decrease of about 50%) and weaker in the lung (about 20%). To elucidate the mechanism of this action of rimantadine, experiments were carried out with some model systems. The capability of rimantadine to scavenge superoxide radicals (scavenging properties) was studied in a system of xanthine-xanthine oxidase to generate superoxide. The amount of superoxide was measured spectrophotometrically by the NBT-test and chemiluminesce. Rimantadine does not show scavenging properties and its antioxidant effect observed in vivo, is not a result of its direct action on the processes of lipid peroxidation and/or interaction with antioxidant enzymes. The antioxidant properties of rimantadine were investigated by measurement of induced lipid peroxidation in a Fe2+ and (Fe2+ - EDTA) system with an egg liposomal suspension. Our findings with model systems do not prove an antioxidant or prooxidant effect of the drug on the processes of lipid peroxidation. Apparently, the observed antioxidant effect of rimantadine in vivo is not connected directly with free radical processes in the organism.

Animals↗
PubMed1984

Development of a model system to evaluate methods for radiolabeling monoclonal antibodies.

We have developed a model system that can be used to evaluate methods for radiolabeling monoclonal antibodies. In this system, dinitrophenyl (DNP) is used as a model antigen, and HDP-1 (a monoclonal antibody specific for DNP) is used as a model monoclonal antibody. DNP-coupled agarose beads are injected into the femoral veins of rats, after which they localize in the animals' lungs. Radiolabeled antibody can then be injected and its biodistribution monitored. We describe here the development and initial testing of the model with radioiodinated antibody.

Animals↗
PubMed1999

Characterization of the Batl (Bacteroides aerotolerance) operon in Bacteroides fragilis: isolation of a B. fragilis mutant with reduced aerotolerance and impaired growth in in vivo model systems.

YT135.2.8, a Tn4400' insertion mutant of Bacteroides fragilis strain TM4000, grows poorly when used to infect Monika or Chinese hamster ovary (CHO) cell monolayers and is outcompeted by wild-type strains in mixed infections. YT135.2.8 also shows defects in the rat granuloma pouch model system in monoculture and is completely outcompeted by the wild-type strain in a mixed infection. In addition, this mutant shows defects in a new model system consisting of CHO suspension cell columns. All of these defects may be explained by the finding that YT135.2.8 shows decreased tolerance to exposure to atmospheric oxygen (less aerotolerant). The monolayer growth defect (MGD) of YT135.2.8 can be influenced significantly by the presence of sulphur-containing reducing agents (cysteine, dithiothreitol, thiodiglycol) or the non-sulphur reducing agent Tris-(2-carboxylethyl)phosphine (TCEP). The defects in YT135.2.8 can be complemented by a 6.6 kb fragment of the B. fragilis chromosome. DNA sequencing of this fragment and of the regions flanking the Tn4400' insertion in the B. fragilis chromosome revealed the presence of five open reading frames, corresponding to genes bat (Bacteroides aerotolerance) A, B, C, D, E, which form the Batl operon; Tn4400' inserted within batD. All of the hypothetical proteins possess one or more membrane-spanning domains. BatA and BatB show high similarity to each other but, like BatD, they show no match to sequences of known function in the databases. BatC and BatE contain 2-4 repeated sequences similar to the tetratricopeptide repeats (TPRs) seen in many eukaryotic proteins. The function of TPR sequences in protein interactions in other systems leads to the suggestion that the Bat proteins form a complex. The Batl complex may be involved in the generation or export of reducing power equivalents to the periplasm of the B. fragilis cell.

Amino Acid Sequence↗
PubMed1983

Systems planning for the 80s: the Nebraska Mental Health Desired Service System model.

In an effort to address the complex realities of mental health service delivery in the 1980s, a systems model for planning and policy making has been developed. The model, called "the Nebraska Mental Health Desired Service System," can serve as a template for future service delivery system design. The development of the model and issues attendant to it are presented. Application of the model to planning, fiscal management, system management, politics, human resources development, and services coordination is presented.

Health Planning Organizations↗
PubMed1999

Partition Coefficients and Interfacial Activity for Polar Components in Oil/Water Model Systems.

Partition coefficients, surface tension, and interfacial tension for some polar organic components dissolved in oil/water model systems have been investigated. The systems consist of isooctane modeling the oil phase and of water solutions of NaCl and CaCl2 modeling the water phase. The organic compounds examined were 1-naphtoic acid, 5-indanol, and quinoline, all well-defined molecules known to be representative of polar components in crude oil. The dependence on pH, salinity, and ionic strength in the water phase was investigated. The surface tension and interfacial tension were also examined as a function of component concentration. The results show a connection between the distribution of the polar components and the interfacial tension. Correspondence between the partition coefficient and the pKa value for the components is also reported. For 1-naphtoic acid none of the two ionization forms of the molecule are found to be surface active in aqueous solution. For 5-indanol both forms are surface active, and for quinoline only the nonionic form of the molecule is found to be surface active. The results indicate that the aqueous phase is the one that governs the interfacial tension. Increasing salinity increases the concentration of the component in the oil phase and decreases the interfacial tension between the oil phase and the aqueous phase. The results are explained due to the "salting-out" effect and to changes in the electrostatics for the various systems. Copyright 1999 Academic Press.

Journal Article↗
PubMed1990

An in vivo model system for the study of avian osteoclast recruitment and activity.

We have developed a model system for the study of osteoclast recruitment and activity using devitalized bovine cortical bone slices implanted onto the chorioallantoic membrane (CAM) of chicken embryos. Bone slices were examined after 3, 6, and 8 days of incubation on the CAM. A marked cellular reaction to the bone was observed, characterized by a prominent angiogenic response. Upon histological examination, numerous multinucleated giant cells were associated with the undersurface of the bone slice and concentrated towards its periphery. These multinucleated cells were often associated with resorption lacunae and demonstrated ruffled borders when viewed by transmission electron microscopy. Removal of the cells and examination of the bone surface by scanning electron microscopy revealed numerous resorption pits characteristic of osteoclastic activity. These pits were evident on day 3 of incubation and appeared to be more extensive by day 8. This work demonstrates that the cells recruited to such ectopically implanted devitalized bone slices are functional osteoclasts, and that this system may provide a useful model for the study of osteoclast recruitment and activity.

Animals↗
PubMed2004

Caenorhabditis elegans as a model system for triplet repeat diseases.

Common features underlie the generation and function of neurons in multicellular animals. It is likely that conserved pathways and genes also are involved in neuronal degeneration and malfunction. To address the molecular mechanisms of complex human neurological disorders, many investigators are choosing to study these diseases in simpler organisms. The nematode Caenorhabditis elegans provides an excellent model system to address genetically the mechanisms of triplet repeat diseases. Advantages of using C. elegans as a model system include the ease of genetic manipulation, the sequenced genome, and a short life cycle. Furthermore, researchers can precisely identify specific neurons and follow their development or survival throughout the animal's lifetime. This chapter describes the tools and approaches for modeling triplet repeat diseases in C. elegans with a specific emphasis on polyglutamine (polyQ) diseases. Although the bulk of the chapter is devoted to generating a polyQ disease model in C. elegans, it also addresses potential avenues for assessing the impact of specific candidate genes/pathways on the disease process, including cell death and aging.

Animals↗
PubMed1990

Human sperm and hamster oocyte interaction: a model system to assess sperm entry into the oocyte after partial zona dissection.

A model system of hamster oocyte and human sperm interaction was used to assess sperm entry into the perivitelline space after partial zona dissection. The procedure of zona dissection was standardized by creating slits which included one fourth, one eighth, one eighth X 2, or one sixteenth of the zonal circumference. Manipulated eggs were allowed to interact with 1 X 10(6) sperm/mL for 3 hours. A single large or medium slit was equally effective in permitting sperm entry into 46% and 47% of the manipulated eggs, respectively. However, the longer slit doubled the average number of sperm detected in the perivitelline space. A second medium-sized slit increased the rate of sperm entry into the perivitelline space to 76%, but the incidence of damaged oocytes also increased. A small slit did not permit sperm entry into any of the manipulated oocytes. This heterologous system of gamete interaction provides a model to evaluate requirements for successful partial zona dissection or other related procedures for assisted fertilization in the human.

Animals↗