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Biomedical subjects

V Speth

Publications and source records attributed to V Speth.

At least 37 records · Page 2Linked to original sources
PubMed1981

Filamentous structures in adherent Mycoplasma pneumoniae cells treated with nonionic detergents.

Mycoplasma pneumoniae cells adhering to glass or Parlodion-coated grids were extracted with Triton X-100. The extracted cells showed a cytoskeleton consisting of a rodlike tip structure and a filamentous network in the cytoplasm. The tip structure was up to 300 nm long and approximately 40 nm wide ending at the distal end in a bleb-like structure, and seemed to consist of filaments arranged in parallel, 4.8 +/- 0.5 nm wide. In the cytoplasm the filaments formed an irregular lattice. Similar filaments were found in platinum replicated critical-point dried extracted cells. An actinlike nature of the filaments is suggested by some of their properties, but the degree of homology with respect to eucaryotic actin is still unknown. The filaments were sensitive to protease treatment but stable in high molar KCl solutions. They were apparently destroyed by incubation in high molar KI solution, leaving only some parts of the tip structure. Formaldehyde-fixed M. pneumoniae cells treated with Triton X-100 bound rhodamine-labeled phalloidin specifically. Furthermore, they could be stained with antiactin antibodies. Binding of myosin subfragment 1 to the filaments was not observed.

Actins↗
PubMed1981

Participation of pili and cell wall adhesion in the yeast agglutination activity of Escherichia coli.

Escherichia coli strain 2699 (O6:K13) which had been isolated from a case of urinary tract infection exhibited pili during the stationary phase (24 to 40 h), but not during the exponential phase (4 h), when grown in static broth culture. The bacteria were also piliated when grown for 24 h on agar. They agglutinated Saccharomyces cerevisiae (baker's yeast) in the piliated as well as in the nonpiliated state. The agglutinations were mannose sensitive, i.e., they could be inhibited with 50 mM methyl-alpha-mannoside. The bacteria were first depiliated by shearing and then used for the isolation of outer membrane vesicles with an Omnimixer. Purified pili and outer membranes were characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and electron microscopy. The pili could be demonstrated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis only after treatment at low pH or in saturated guanidine hydrochloride which is typical of the common type 1 pili. Depiliated bacteria, purified pili, and purified outer membranes gave mannose-sensitive agglutination of S. cerevisiae. The findings are discussed with respect to possible mechanisms of cell agglutination.

Agglutinins↗
PubMed1981

Morphological characterization of the plasma membrane of a pituitary tumor cell line (GH3).

Freeze-fracturing and deep-etching have been used to characterize the internal morphology and surface charge of the plasma membrane of GH3-cells from cell culture in fixed and unfixed material. Glutaraldehyde does not effect intramembrane particle pattern but induces structural modifications on the cell surface in a way that additional attachment sites for cationized ferritin are exposed at specific areas of the membrane. Negative surface charges are not directly linked to the intramembrane particles, but to other (surface-) proteins, independently enough to be dislocated by external ligands; this process is restricted to the membrane surface. Thermotropic phase changes induce separation of lipidic regions from proteinaceous regions. Peripheral and integral protein are thus aggregated simultaneously, resulting in clustered membrane particles and aggregated surface charges.

Animals↗
PubMed1980

Action of prostaglandin E1 and F2 alpha on the pinocytic activity of horseradish peroxidase in bone-marrow derived macrophages.

The influence of prostaglandin E1 and F2 alpha on the pinocytic activity of bone-marrow macrophages was studied biochemically and morphometrically. The results show that prostaglandin E1 induces 44% inhibition of pinocytosis of horseradish peroxidase; prostaglandin F2 alpha has no significant effect. Morphometrical analysis of electron micrographs demonstrates that inhibition of pinocytosis is connected with diminished average size and raised number of pinocytic vesicles. The influence of prostaglandin E1 on pinocytosis is fully reversible. Further experiments are needed to explore the molecular mechanism of the prostaglandin E1 induced alteration of membrane function.

Animals↗
PubMed1979

Rapid alterations in cellular morphology and plasma membrane structure induced in rat thymocytes by mitogenic stimuli.

Under conditions where a maximum stimulation of 3-O-methyl-glucose transport is observed, three thymocyte mitogens (concanavalin A, ionophore A23187 and hydrogen peroxide) cause cell rounding and a decrease in the density of intra-membrane particles on the plasma membrane. The early effects of mitogens on the thymocyte plasma membrane are similar to those of osmotic shock.

Animals↗
PubMed1978

Complement lysis: the ultrastructure and orientation of the C5b-9 complex on target sheep erythrocyte membranes.

The C5b-9 complex derived from human serum and assembled on target sheep erythrocyte membranes is a thin-walled cylinder rimmed by an annulus at one end. The total height of the cylinder is 150 A, towards which the annulus contributes 30 A. The cylinder has an apparently uniform internal diameter of 100 A. The external diameter of the annulus is 200 A. The classical complement 'rings' visualized on membranes after complement lysis represent such C5b-9 cylinders perpendicularly oriented on the membranes. The thin-walled cylinder is anchored in the membrane matrix and the annulus located in the exterior membrane glycocalyx. At the sites of attachment of the C5b-9 complexes, the continuity of the membrane bilayer is disturbed and the presence of trans-membrane pores is indicated. The data essentially support the 'doughnut' theory of complement lysis.

Animals↗
PubMed1975

Thermotropic lipid clustering in tetrahymena membranes.

The effect of temperature on the core structure of endoplasmic reticulum membranes has been visualized directly in cells of the poikilothermic eukaryote Tetrahymena pyriformis by freeze-etch electron microscopy. Moreover, the effect of temperature on the smooth microsomal membrane vesicles isolated from these cells, as well as on the extracted membrane lipids, has been examined by fluorescence probing, electron spin resonance, proton nuclear magnetic resonance, and calorimetry. Freeze-etch electron microscopy of T. pyriformis cells, equilibrated at different temperatures between 28 and 5 degrees, reveals the emergence of smooth areas on the fracture faces of endoplasmic reticulum membranes at temperatures below similar to 17 degrees. In this temperature range, we also find discontinuities in the glucose 6-phosphatase activity, in the fluorescence intensity of 8-anilino-1-naphthalensulfonate, in the partition of 4-doxyldecane, and in the separation of the outer hyperfine extrema of 5-doxylstearic acid in the microsomal membranes. These membranes apparently contain at least two lipid environments of different fluidity as indicated by the 12-doxylstearic acid spin-label. Proton nuclear magnetic resonance of the extracted membrane lipids indicates an abrupt change of the fatty acid chain mobilities at temperatures below similar to 17 degrees. This, however, is not due to a true thermal liquid crystalline in equilibrium crystalline phase transition. Calorimetric measurements also support this conclusion. The thermotropic alterations observed within the membranes are interpreted to be due primarily to a clustering of "rigid" liquid crystalline lipid environments which exclude membrane-intercalating proteins.

Animals↗
PubMed1974

Reversible, thermotropic alteration of nuclear membrane stucture and nucleocytoplasmic RNA transport in Tetrahymena.

We examine the effect of cooling upon the freeze-etch ultrastructure of nuclear membranes, as well as upon nucleocytoplasmic RNA transport in the unicellular eukaryote Tetrahymena pyriformis. Chilling produces smooth, particle-free areas on both faces of the two freeze-fractured macronuclear membranes. Upon return to optimum growth temperature the membrane-associated particles revert to their normal uniform distribution and the smooth areas disappear. Chilling lowers the incorporation of [(14)C]uridine into whole cells and their cytoplasmic RNA. Cooling from the optimum growth temperature of 28 degrees to 18 degrees C (or above) decreases [(14)C]uridine incorporation into cells more than into their cytoplasmic RNA; chilling to below 18 degrees C but above 10 degrees C causes the reverse. [(14)C]Uridine incorporation into whole cells and their cytoplasmic RNA reflects overall RNA synthesis and nucleocytoplasmic RNA transport, respectively. RNA transport decreases strongly between 20 degrees and 16 degrees C, which is also the temperature range where morphologically detectable nuclear membrane transitions occur. This suggests that the nuclear envelope limits the rate of nucleocytoplasmic RNA transport at low temperatures. We hypothesize that a thermotropic lipid phase transition switches nuclear pore complexes from an "open" to a "closed" state with respect to nucleocytoplasmic RNA transport.

Animals↗