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Biomedical subjects

J Kartenbeck

Publications and source records attributed to J Kartenbeck.

At least 55 records · Page 3Linked to original sources
PubMed1980

Fusion of Semliki forest virus with the plasma membrane can be induced by low pH.

When BHK-21 cells with Semliki Forest virus (SFV) bound at the plasma membrane are briefly treated with low pH medium (pH 5-6), fusion between the viral membrane and the plasma membrane occurs, releasing the viral nucleocapsid into the cytoplasm. The fusion reaction resembles that described previously for Sendai virus but with one fundamental difference; it is strictly dependent on low pH. The fusion reaction is highly efficient. Up to 86% of bound viruses fuse, and 6 X 10(6) virus spike proteins can be inserted into the plasma membrane of each cell. The process is very rapid (full activity is observed after 5 s) and it occurs over a wide temperature range and equally well with all five cell lines tested (BHK-21, HeLa B, HeLa suspension, Raji, and 3T3). Low pH-induced fusion of the virus at the plasma membrane can lead to infection of susceptible cells. The artificial nature of this infection pathway is, however, demonstrated by the facts that infection through the plasma membrane occurs only at subphysiological pH and that it is insensitive to inhibitors of the normal entry route. Nevertheless, these results indicate that low pH membrane fusion introduces the viral genome into the cytoplasm in a form suitable for replication.

Animals↗
PubMed1980

The effects of octylglucoside on the Semliki forest virus membrane. Evidence for a spike-protein--nucleocapsid interaction.

Evidence is presented for a non-covalent interaction between the spike glycoprotein and the nucleocapsid of Semliki Forest virus. When isolated viruses were treated with the non-ionic detergent beta-D-octylglucoside at neutral pH and low ionic strength the lipid bilayer membrane could be removed leaving most of the spike glycoproteins attached to the nucleocapsids. The interaction between capsids and membrane protein was sensitive to elevated pH and ionic strength, but at least partially reversible at neutral pH and low ionic strength. The possible role of this interaction in the viral structure and in the mechanism of budding of the virus from the host cell is discussed.

Animals↗
PubMed1979

B-type cytochromes in plasma membranes isolated from rat liver, in comparison with those of endomembranes.

Fractions of plasma membranes, Golgi apparatus, endoplasmic reticulum (ER), and nuclear envelope were isolated from rat liver and were characterized by electron microsocpe and biochemical methods. The purity of the fractions was controlled by morphometry and by marker enzyme activities. Amounts of cytochromes b5, P-450, and P-420 were measured, as well as the NADPH- and NADPH-cytochrome c reductase activities. The pigments of the microsomal electron transport system were found in all membrane fractions in relatively high amounts, thus excluding an origin by microsomal contamination. Purified preparations of plasma membrane and Golgi apparatus contained approximately 30% of the cytochrome b5 and cytochrome P-450 + P-420 found in ER membranes. Plasma membranes were also characterized by a high ratio of P-420/450. Degradation of cytochromes P-450 and P-420 was relatively rapid in all fractions, except in the ER. Cytochrome b5 extracted from plasma membranes was spectrophotometrically and enzymatically indistinguishable from ER cytochrome b5. However, immunnlogical characterization with rabbit antibodies against the trypsin-resistant core of microsomal cytochrome b5 showed the presence of at least two types of cytochrome b5 in ER membranes, in contrast to the plasma membranes in which only one of these components was detected. This immunological differentiation also demonstrates that the plasma membrane-bound cytochrome b5 is endogenous to this membrane and does not reflect contamination by ER elements. We conclude that cytochromes b5, P-450, and P-420 are not confined only to ER and nuclear membranes but also occur in signficant amounts in Golgi apparatus and plasma membranes. The findings are discussed in relation to observations of similar redox components in Golgi apparatus, secretory vesicles, and plasma membranes of other cells.

Animals↗
PubMed1978

Preparation of membrane-depleted polygonal coat structures from isolated coated vesicles.

When coated vesicles isolated from porcine brain are treated with buffers containing 2 M urea and subjected to ultracentrifugation, pellets are obtained which consist of largely smooth-surfaced, i.e. coat-free, vesicles. On dialysis of the urea from the supernatant solution spheroidal particles can be pelleted which are of similar size to the coated vesicles and show the typical polygonal lattice arrays but do not reveal any vesicle membrane profiles. Gel electrophoresis of these membrane-depleted polygonal arrangements demonstrates the predominance, if not exclusive occurrence, of the polypeptide band component with an apparent molecular weight of about 180,000. This suggests that the polygonal coat structure contains only clathrin.

Animals↗
PubMed1977

Reconstitution of Semliki forest virus membrane.

The spike glycoproteins of the Semliki forest virus membrane have been incorporated into vesicular phospholipid bilayers by a detergent-dialysis method. The detergent used was beta-D-octylglucoside which is nonionic and has an exceptionally high critical micellar concentration which facilitates rapid removal by dialysis. The vesicles obtained were of varying sizes and had spikes on their surface. Two classes of vesicles were preferentially formed, small protein-rich and large lipid-rich (average lipid to protein weight ratios, 0.22 and 3.5, respectively). Both classes of vesicles retained the hemagglutinating activity of the virus. The proteins were attached to the lipid bilayer by hydrophobic peptide segments, as in the viral membrane. Most of the proteins were accessible to proteolytic digestion from the outside, suggesting an asymmetric orientation.

Centrifugation, Density Gradient↗
PubMed1976

Experimental disintegration of the nuclear envelope. Evidence for pore-connecting fibrils.

The disintegration of the nuclear envelope has been examined in nuclei and nuclear envelopes isolated from amphibian oocytes from amphibian oocytes and rat liver tissue, using different electron microscope techniques (ultrathin sections and negatively or positively stained spread preparations). Various treatments were studied, including disruption by surface tension forces, very low salt concentrations, and nonionic detergents such as Triton C-100 and Nonidet P-40. The highest local stability of the cylinders of nonmembranous pore complex material is emphasized. As progressive disintegration occurred in the membrane regions, a network of fibrils became apparent which interconnects the pore complexes and is distinguished from the pore complex-associated about 15-20 nm thick, located at the level of the inner nuclear membrane, which is recognized in thin sections to bridge the interpore distances. With all disintegraiton treatments a somewhat higher susceptibility of the outer nuclear membrane is notable, but a selective removal does not take place. Final stages of disintegration are generally characterized by the absence of identifiable, membrane-like structures. Analysis of detergent-treated nuclei and nuclear membrane fractions shows almost complete absence of lipid components but retention bo significant amount of glycoproteins with a typical endomembrane-type carbohydrate pattern. Various alternative interpretations of these observations are discussed. From the present observations and those of Aaronson and Blobel (1,2), we favor the notion that threadlike intrinsic membrane components are stabilized by their attachment to the pore complexes, and perhaps also to peripheral nuclear structures,and constitute a detergent-resistant, interpore skeleton meshwork.

Animals↗
PubMed1976

Involvement of vesicle coat material in casein secretion and surface regeneration.

The ultrastructure of the apical zone of lactating rat mammary epithelial cells was studied with emphasis on vesicle coat structures. Typical 40-60 nm ID "coated vesicles" were abundant, frequently associated with the internal filamentous plasma membrane coat or in direct continuity with secretory vesicles (SV) or plasma membrane proper. Bristle coats partially or totally covered membranes of secretory vesicles identified by their casein micelle content. This coat survived SV isolation. Exocytotic fusion of SV membranes and release of the casein micelles was observed. Frequently, regularly arranged bristle coat structures were identified in those regions of the plasma membrane that were involved in exocytotic processes. Both coated and uncoated surfaces of the casein-containing vesicles, as well as typical "coated vesicles", were frequently associated with microtubules and/or microfilaments. We suggest that coat materials of vesicles are related or identical to components of the internal coat of the surface membrane and that new plasma membrane and associated internal coat is produced concomitantly by fusion and integration of bristle coat moieties. Postexocytotic association of secreted casein micelles with the cell surface, mediated by finely filamentous extensions, provided a marker for the integrated vesicle membrane. An arrangement of SV with the inner surface of the plasma membrane is described which is characterized by regularly spaced, heabily stained membrane to membrane cross-bridges (pre-exocytotic attachment plaques). Such membrane-interconnecting elements may represent a form of coat structure important to recognition and interaction of membrane surfaces.

Animals↗
PubMed1976

Involvement of bristle coat structures in surface membrane formations and membrane interactions during coenocytotomic cleavage in caps of Acetabularia mediterranea.

In the multinucleate cap rays of the green alga Acetabularia mediterranea the cell surface increases dramatically within a short time period during the final stages of coenocytotomic cleavage. In early stages of cyst formation the cytoplast is traversed by numerous large and prolate cleavage vesicles which are characterized by typical columellar or spinous coat structures. The cleavage vesicles are closely associated with the surface of plastids and, to a lesser degree, of mitochondria. This intimate association seems to be mediated by regularly spaced, densely stained intermembranous cross-bridge structures and is maintained throughout cleavage. These cleavage vesicles contain a finely fibrillar material structurally similar to the hyaline layer of mucilage that fills the space between the plasma membrane and cell wall. They line up with invaginations of the plasmalemma and vacuole membranes and, together with smaller vesicles interspersed, constitute preformed "perforation lines" for the final separation of the coenoblast portions. Equidistantly spaced plaques of attachment of such vesicles with surface membrane are described. We hypothesize (a) that the cleavage vesicle membrane is the immediate precursor to the new postcoenocytotomic surface membrane, (b) that the cleavage vesicle coat structures are integrated into the subsurface coat of the plasma membrane, (c) that growth of the laterally attached cleavage vesicles by intussusception of small fuzzy-coated vesicles is confined to their "free ends," (d) that the intermembranous cross-bridge elements are related to bristle coat structures and play a role in the establishment of the cleavage lines, and (e) that the coenocytotomic cleavage process is organized so that adjacent plastids are separated in a way that guarantees the inclusion of several plastids in each cyst.

Acetabularia↗