Gene/Protein Disease Symptom Drug Enzyme Compound
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 12,197 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

After injection of the L7 dorsal root ganglion with 3H-leucine, fast axoplasmic transport carries some 3--5 x more labeled materials down the sensory fibers branches entering the sciatic nerve as compared to the dorsal root fiber branches of the neurons. Freeze-substitution preparations taken from the two sides of the lumbar seventh dorsal root ganglia of cats and monkeys showed little difference in the histograms of nerve fiber diameters of the sensory nerve fiber branch of these neurons as compared to the dorsal root fiber branches. A similar density of microtubules and of neurofilaments in the dorsal root and sensory nerve fiber branches over a wide range of fiber diameters was found in electron micrograph preparations. In the absence of an anatomical difference in the fibers to account for the asymmetrical outflow, a functional explanation based on the transport filament model was advanced.
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PMID:Routing of transported materials in the dorsal root and nerve fiber branches of the dorsal root ganglion. 8 50

Electron microscopy of thin sections and freeze etch replicas of the eggs of the nematodes Trichuris suis and T. muris is used to provide evidence in support of the Bouligand hypothesis of helicoidal architecture. The evidence presented is as follows: 1. The specific objections to the Bouligand model raised by Dennell (1974) and Dalingwater (1975b) are answered by reference to a pyramid of helicoidal tissue in which the corners are blunt. 2. Sections cut normal to the plane of the laminae do not show parabolic patterning. Parabolae appear if the section is tilted--their direction depending upon the direction of tilting. 3. Freeze etching allows the direct visualization of helicoidal architecture. Fibres are parallel within any one lamina but the fibre direction rotates by an angle of 9 degrees in successive laminae. Parabolic arcs are made up of short lengths of straight fibres--curved fibres were not observed. Planes of sectioning producing single and double spiral artifacts are described and the formation of these artifacts discussed. The sense of rotation of the helicoid is shown to be asymmetrical about any mid-plane through the egg.
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PMID:The trichurid egg-shell: evidence in support of the Bouligand hypothesis of helicoidal architecture. 74 39

1. ADP/ATP transport has been reconstituted by incorporation of the purified carrier protein in liposomes filled with ATP. The transport was assayed by uptake of [14C]ADP into the liposomes, and by release of ATP as determined by a luminescence technique. [14C]ADP uptake was strictly dependent on internal ATP. 2. The simplest phospholipid system capable of yielding high rates of ADP/ATP transport was a mixture of phosphatidylethanolamine and cariolipin (92: 8, w/w). 3. ADP/ATP transport in the reconstituted system proceeded by exchange-diffusion with a 1/1 stoichiometry. The specificity for aDP and ATP was absolute. The capacity and the rate of exchange depended on the concentration of ATP present in liposomes. The rate of transport at 20 degrees C, at 20 mM internal ATP, routinely ranged between 300 and 1000 nmol of nucleotide exchanged per min/mg of added carrier protein. The apparent Km value for external ADP was around 10 microM. 4. The ADP/ATP exchange in the reconstituted system was rather stable to ageing. It dropped by only 20% after 1 day of ageing at 20 degrees C. Divalent cations (Mg2+, Mn2+, Ca2+) at concentrations higher than 1 to 2 mM had a deleterious effect on ADP/ATP transport, concomitant with the release of internal ATP and accumulation of multilamellar vesicles. 5. Atractyloside behaved as a competitive inhibitor and carboxyatractyloside as a non-competitive inhibitor. Bongkrekic acid required a slightly acidic pH to be inhibitory. The data concerning atractyloside, carboxyatractyloside and bongkrekic acid were similar to those obtained with whole mitochondria, suggesting that the carrier protein in liposomes has the same asymmetrical arrangement as in the mitochondria. 6. The percentage of competent carrier protein in liposomes was calculated from dose-response data concerning the inhibition of ADP/ATP transport by atractyloside or carboxyatractyloside, and from the amount of bound [3H]-atractyloside removable by ADP. By both methods, 3 to 6% of the added carrier protein was found to be competent in ADP/ATP transport, based on the assumption that the binding of one atractyloside or carboxyatractyloside molecule per 30000 molecular weight carrier unit results in complete inhibition of transport. 7. Freeze-fracture electron microscopy showed that the ADP/ATP carrier protein-lipid preparations are formed by small vesicles, most of which give rise to smooth fracture faces (probably pure lipid vesicles). Only a small percentage of the vesicles (2 to 4% depending on the amount of carrier protein added) were clearly particulated. About 90% of the particulated vesicles showed no more than 2 particles per vesicle and only 5% more than 5 particles per vesicle. The distribution of the particles between convex and concave fracture faces was asymmetric; about 2/3 of the protein molecules were anchored at the external surface of the vesicles and only 1/3 at the internal one...
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PMID:Kinetic, binding and ultrastructural properties of the beef heart adenine nucleotide carrier protein after incorporation into phospholipid vesicles. 625 72

Cytochrome P450scc can be reconstituted successfully into large unilamellar phospholipid vesicles by a combined octylglucoside dialysis/adsorption method. Freeze-fracture electron microscopy was used to analyze the morphology, distribution, and protein topology of the cytochrome P450scc vesicles in dependence on lipid composition. Particles were observed only in close contact to the vesicle surface, probably representing tightly associated cytochrome P450scc at the outer vesicle surface. In cytochrome P450scc vesicles similar in lipid composition to the inner membrane of bovine mitochondria direct evidence by freeze-fracturing was found for a specific cytochrome P450scc-induced aggregation of the vesicles. The vesicle aggregation critically depends on the content of the specific mitochondrial membrane constituent cardiolipin. The aggregation and thus the intervesicular contacts were observed to be inhibited by both addition of anti-cytochrome P450scc IgG and adrenodoxin. Enzymatic reduction of cytochrome P450scc in the liposomal membrane by its electron transfer partners completely indicates an asymmetrical localization in/at the outer side of the bilayer membrane. It is suggested that vesiculation of the inner mitochondrial membrane may be a consequence of the characteristic cardiolipin-dependent cytochrome P450scc membrane topology: the cardiolipin binding, peripheral, non-bilayer-spanning integration as an oligomer in the outer leaflet of the membrane may play a role in the dynamics of formation and dissociation of intramitochondrial vesicles with a functional importance for steroidogenesis.
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PMID:Direct visualization of a cardiolipin-dependent cytochrome P450scc-induced vesicle aggregation. 773 45

We built a passive compartmental model of a cortical spiny stellate cell from the barrel cortex of the mouse that had been reconstructed in its entirety from electron microscopic analysis of serial thin sections (White and Rock, 1980). Morphological data included dimensions of soma and all five dendrites, neck lengths and head diameters of all 380 spines (a uniform neck diameter of 0.1 micron was assumed), locations of all symmetrical and asymmetrical (axo-spinous) synapses, and locations of all 43 thalamocortical (TC) synapses (as identified from the consequences of a prior thalamic lesion). In the model, unitary excitatory synaptic inputs had a peak conductance change of 0.5 nS at 0.2 msec; conclusions were robust over a wide range of assumed passive-membrane parameters. When recorded at the soma, all unitary EPSPs, which were initiated at the spine heads, were relatively iso-efficient; each produced about 1 mV somatic depolarization regardless of spine location or geometry. However, in the spine heads there was a twentyfold variation in EPSP amplitudes, largely reflecting the variation in spine neck lengths. Synchronous activation of the TC synapses produced a somatic depolarization probably sufficient to fire the neuron; doubling or halving the TC spine neck diameters had only minimal effect on the amplitude of the composite TC-EPSP. As have others, we also conclude that from a somato-centric viewpoint, changes in spine geometry would have relatively little direct influence on amplitudes of EPSPs recorded at the soma, especially for a distributed, synchronously activated input such as the TC pathway. However, consideration of the detailed morphology of an entire neuron indicates that, from a dendro-centric point of view, changes in spine dimension can have a very significant electrical impact on local processing near the sites of input.
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PMID:Electrical consequences of spine dimensions in a model of a cortical spiny stellate cell completely reconstructed from serial thin sections. 852 Dec 82

A total of 460 roots of extracted human teeth were divided into three groups i.e. straight, apically curved and entirely curved groups. Each of the three groups were divided into seven subgroups according to instrumentation by conventional hand, K-Flex file, 3-LD, 3-LDSY, Excalibur. MM 1400 and Endo Sonic. Radiographs were taken both clinical and proximal views before and after the enlargement of canals. An assessment of shaping characteristic of instrumentation was made on the basis of overimposed radiographs including perforation, ledge formation smoothness of wall contour incidence of elbow and zip measurements at the elbow level and asymmetry measurements. The majority of enlarged root canals were asymmetrical in shape. High differences were found between the incidence of elbow and zip formation. Under laboratory conditions the K-Flex file produced minor canal aberrations and significantly less asymmetry than the conventional instruments. But both the above mentioned instruments caused perforations on curved canals, such as the instrumentation by Excalibur. The loss of working distance was significant in all canal forms prepared with 3-LD and 3-LDSY instruments, which could have occurred through the packing of debris towards the apical constriction. The Excalibur appeared to be superior to the conventional hand instrument in straight canals, but its shaping characteristic was similar to conventional hand instrument in curved canals. The MM 1400 handpiece and ultrasonic instruments resulted in less aberration and significantly less asymmetry than the other tested instruments.
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PMID:[Comparative evaluation of different instruments for root canal preparation tested on extracted human teeth III. Study of sonic and ultrasonic instruments]. 862 Sep 78

Freeze-fracture electron microscopy was applied to study membrane morphology in a phosphatidylethanolamine-deficient E. coli strain. For growth, this strain requires millimolar concentrations of specific divalent cations like Mg2+ or Ca2+. These cations bring the bilayer to nonbilayer phase transition temperature of the lipids back to wild type levels by shifting the phase preference of cardiolipin in the membrane towards the inverted hexagonal (H(II)) phase. Under growth conditions, these cells show a bilayer based membrane with an intramembrane particle distribution as in wild type cells. Upon lowering the temperature, smooth areas are observed corresponding to gel state lipid bilayer domains. Ca2+ was used to manipulate the phase behavior of the membrane lipids in situ. Exposing the cells to Ca2+ up to 100 mM at 42 degrees C did not result in the appearance of nonbilayer structures, despite the fact that in total lipid extracts under these conditions the hexagonal H(II) phase was observed. However, the addition of a Ca2+ ionophore, which leads to exposure to Ca2+ of both faces of the plasma membrane, gives rise to formation of H(II) phase, stacked bilayer domains and blebbing upon addition of 50 mM CaCl2 at 42 degrees C. We conclude that the asymmetrical localization of divalent cations in the periplasm of this strain allows them to be functionally effective while membrane stability is maintained.
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PMID:A freeze-fracture study of the membrane morphology of phosphatidylethanolamine-deficient Escherichia coli cells. 909 13

The objective of this study was to evaluate the shaping characteristics of various root canal instruments using human teeth. A total of 420 extracted human roots were embedded in resin blocks. The embedded roots were divided into three groups, i.e. roots with (i) straight, (ii) apically curved, and (iii) whole-length curved canals according to the Schneider's angle and the length of the radius of arc fitting the curvature of root canals. Each of the three groups containing 140 roots were randomly divided into seven subgroups prior to preparation. The canals were prepared manually with traditional and flexible instruments, engine driven Racer-type, Giro-type, randomly vibrating instruments and with sonic and ultrasonic instruments. The shortcomings of the seven preparation methods were assessed by the superimposition of projected radiographs taken in bucco-lingual and mesio-distal views before and after the preparation. The prepared straight canals showed a high percentage (75.7%) of apical asymmetry. Coronal transposition of the apical stop was graded with higher scores in all canal forms prepared with Racer-type and Giro-type instruments, which could have occurred through packing of debris towards the apical constriction. The majority of the prepared curved canals were asymmetrical in shape. The location of the aberrations depended on the original shape of the canal but the method of shaping also had a decisive effect on the post-operative form of the canal. Large differences were found between the incidence of elbow (11.7-40.0%) and zip (75.7-80.0%). K-Flex files produced minor canal aberrations and significantly less asymmetry (P < 0.05) than the conventional hand instruments. The MM 1400 handpiece and ultrasonic instruments were associated with less aberration and significantly less asymmetry than the other instruments tested. The Excalibur appeared to be superior to the conventional hand instruments in straight canals, but its shaping characteristics were similar to conventional instruments in curved canals. Under the conditions of this study, canal shaping with Cavi Endo, MM 1400 and K-Flex files appeared to be superior to that achieved with conventional hand instruments Excalibur, Intra Lux Endo Kopf 3LDSY, and 3LD instruments.
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PMID:A comparative study of seven instruments in shaping the root canal in vitro. 1033 46

Sugar transport through maltoporin of Escherichia coli was investigated. This protein facilitates maltooligosaccharide translocation via a binding site in the channel. Because incorporation of the protein into the bilayer results in randomly orientated channels, we re-examined the postulated symmetric translocation model by reconstitution of maltoporin under an externally applied field. Upon binding of bacteriophage lambda, which exploit surface-exposed loops of maltoporin as the receptor, sugar permeation, but not the ion current, was blocked. Thus using the phage-to-probe orientation we were able to show that the channels were approximately 80% directionally inserted into the bilayer. Moreover, asymmetry of the channel was revealed because sugar entrance through the 'open' periplasmic side of maltoporin was similarly reduced. Here a new asymmetrical two-barrier model is presented. Based on liposome-swelling assays and current-fluctuation analysis we conclude that the periplasmic side of the porin shows a two- to threefold higher energy barrier than the extracellular loop-side of the channels.
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PMID:Oriented channels reveal asymmetric energy barriers for sugar translocation through maltoporin of Escherichia coli. 1060 53

Molecular dynamics simulations of an archaeal membrane made up of bipolar tetraether lipids and a dipalmitoylphosphatidylcholine (DPPC) lipid membrane were performed and compared for the first time. The simulated archaeal membrane consists of a pure monolayer of asymmetrical lipids, analogous to the main polar lipid [MPL; Swain, M., Brisson, J.-R., Sprott, G.D., Cooper, F.P., and Patel, G.B., (1997) Identification of beta-L-Gulose as the Sugar Moiety of the Main Polar Lipid of Thermoplasma acidophilum, Biochim. Biophys. Acta 1345, 56-64] found in T. acidophilum, an extremophile archaeal organism. This simulated membrane lipid contains two cyclopentane rings located on one of the two aliphatic chains of the lipid. The archaeal membrane is simulated at 62degreesC, slightly above the optimal growth temperature of T. acidophilum. We compared the organization of this tetraether lipid monolayer with a DPPC bilayer simulated at 50degreesC, both of them being modeled in a partially hydrated state. Our results assess the singularity of the tetraether lipid organization, in particular the influence of the spanning structure on the molecular ordering within the archaeal membrane.
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PMID:A molecular dynamics study of an archaeal tetraether lipid membrane: comparison with a dipalmitoylphosphatidylcholine lipid bilayer. 1638 74


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