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Biomedical subjects

A Loyter

Publications and source records attributed to A Loyter.

At least 91 records · Page 5Linked to original sources
PubMed1980

Alteration of lymphocyte surface properties by insertion of foreign functional components of plasma membrane.

We report the successful coreconstitution of solubilized lymphocyte plasma membranes and Sendai virus envelopes into membrane vesicles that possess the ability to fuse efficiently with mouse splenocytes of thymocytes to give fully viable cells with modified surface properties. Integration of donor membrane components into the acceptor cells was demonstrated by chemical, morphological, and immunological methods. Over 40% of the label from vesicles coreconstituted with radiolabeled (with 125I or 3H) lymphocyte membranes was incorporated into the fused cells. Insertion of biotin-labeled membrane components into the membranes of the acceptor cells was shown by electron microscopy with ferritin-conjugated avidin. Transfer of receptors to soybean agglutinin was also demonstrated. When vesicles from thymocyte membranes were fused with B splenocytes, over 50% of the cells were lysed with anti-theta antiserum and complement. Moreover, lymphocytes into which allogeneic membranes were incorporated triggered the autologous cells in the mixed lymphocyte reaction, indicating the functional transfer of major histocompatibility complex antigens. These findings strongly suggest that the transferred membranes were functionally incorporated into the acceptor cell membranes. The technique described opens new ways for elucidation of the role of the lymphocyte membrane in the immune response as well as for the understanding of the structure-function relationship of membrane components in other cells.

Animals↗
PubMed1979

Viral and non-viral induced fusion of pronase-digested human erythrocyte ghosts.

Human erythrocyte ghosts but was able to fuse only iso-human erythrocyte ghosts. Iso- and hypo-human erythrocyte ghosts were incubated with the proteolytic enzyme pronase under isotonic (iso-human erythrocyte ghosts) or hypotonic (hypo-human erythrocyte ghosts) conditions. Gel electrophoresis and electron microscope (freeze-etching) studies revealed that most of the erythrocyte membrane polypeptides were hydrolyzed by pronase under hypotonic conditions. Sendai virus readily agglutinated both pronase-digested iso-human erythrocyte ghosts and hypo-human erythrocyte ghosts were fused by the non-viral fusogenic agent glyceromonooleate. Freeze-etching studies revealed that during fusion the membranes of pronase-digested human erythrocyte ghosts are intermixed.

Erythrocyte Membrane↗
PubMed1979

Involvement of spectrin in membrane fusion: induction of fusion in human erythrocyte ghosts by proteolytic enzymes and its inhibition by antispectrin antibody.

In contrast to intact human erythrocytes, human erythrocyte ghosts can be agglutinated but not fused by Sendai virus. Membrane fusion can, however, be induced in virus-agglutinated erythrocyte ghosts by addition of proteolytic enzymes such as trypsin, papain, or Pronase. When erythrocyte ghosts were reacted with antispectrin antiserum, the antiserum inhibited both the induction of fusion and the proteolysis of the membrane spectrin. The correlation between the membrane fusion process and the membrane cytoskeleton is discussed.

Actins↗
PubMed1979

Implantation of the isolated human erythrocyte anion channel into plasma membranes of Friend erythroleukemic cells by use of Sendai virus envelopes.

Sendai virus envelopes and human erythrocyte band 3 membrane polypeptides were isolated in detergent solutions and coreconstituted into detergent-free vesicle structurally resembling viral envelopes. Formation of hybrid viral envelope-band 3 vesicles (VB3) was demonstrated by immunoprecipitation of VB3 containing 4,4'-diisothiocyano-2,2'-ditritostilbenedisulfonic acid-labeled band 3 in the presence of antiviral antiserum. The hybrid VB3 vesicles displayed agglutination, fusion, and hemolytic properties similar to those of reconstituted viral envelopes. Incubation of VB3 with Friend erythroleukemic cells resulted in fusion-mediated insertion of viral antigens and of band 3 into the plasma membranes of the recipient cells. The presence of band 3 incorporated into Friend erythroleukemic cells was revealed structurally by electron microscopy after staining with ferritin-conjugated anti-human erythrocyte membrane antiserum. Incorporation of band 3, the putative erythrocyte antion channel, led to a marked and specific stimulation of anion exchange in Friend erythroleukemic cells. The viral-mediated insertion of an isolated membrane protein into viable Friend erythroleukemic cells provides a method for studying membrane protein turnover and for assaying reconstituted membrane components such as carriers or channels.

Animals↗
PubMed1979

Use of enzymatic and electron microscopy (freeze-etching) methods for studying ATP-dependent masking of erythrocyte membrane phospholipids.

Membrane phospholipids of ATP-depleted chicken, rat, and toad erythrocytes are more susceptible than fresh cells to hydrolysis by phospholipase C (Bacillus cereus), phospholipase A (bee venom), or the combination of these enzymes and sphingomyelinase. ATP depletion of chicken and rat erythrocytes greatly increased the membrane phospholipid fraction, which can be extracted by dry ether. Trinitrobenzene sulfonic acid attacked about 20% of the phosphatidylethanolamine of fresh chicken erythrocytes and 45% of ATP-depleted chicken erythrocytes. The intramembranous particles on the PF face of fresh chicken, rat, and toad erythrocytes are evenly distributed, while those in the same ATP-depleted erythrocytes are significantly clustered. The average distance between the intramembranous particles in the PF face of fresh chicken erythrocytes is about 13 nm, while in ATP-depleted erythrocytes it is about 30 nm. Studies with chicken erythrocytes revealed that ATP depletion is accompanied by dephosphorylation of certain membrane polypeptides. The correlation of dephosphorylation of membrane polypeptides, exposure of membrane phospholipids, and clustering of intramembranous particles is discussed.

Adenosine Triphosphate↗
PubMed1978

Inhibition of membrane fusion by suppression of lateral movement of membrane proteins.

Chicken erythrocytes were fused either by Sendai virus or by the combination of Ca2+ and ionophore A23187. Intramembrane particles and external anionic sites of cells undergoing fusion were found to acquire the ability to undergo a process of cold-induced clustering (thermotropic separation). Cationized ferritin (200 microgram/ml 5% (v/v) cell suspension) inhibited both the fusion process and the thermotropic separation of intramembrane particles and external anionic sites. The correlation between the mobility of membrane proteins and the fusion process is discussed. It is suggest that an increase in the lateral mobility of membrane proteins is a prerequisite for initiation of membrane fusion.

Binding Sites↗
PubMed1978

Inhibition of conjugation in Tetrahymena pyriformis by cerulenin. Possible requirement for de novo lipid synthesis.

Conjugation in Tetrahymena pyriformis is induced by the mixing of two starved complementary mating types. Addition of the antibiotic cerulenin, a specific inhibitor of de novo lipid synthesis, upon mixing of the mating types inhibited the conjugation process. The inhibition of conjugation was found to be reversible upon washing the cells. Cerulenin inhibited [14C]acetate incorporation into the lipid fraction of the cells, while it did not affect the incorporation of [3H]leucine into proteins. Analysis of the fatty acid composition of the whole cells revealed that during conjugation the ratio of saturated to unsaturated fatty acids is markedly changed. While the ratio of saturated:unsaturated fatty acids is 0.30 in unconjugated cells, it reached a value of 0.45 in conjugated cells.

Animals↗
PubMed1978

Role of Ca++ in virus-induced membrane fusion. Ca++ accumulation and ultrastructural changes induced by Sendai virus in chicken erythrocytes.

Some of the ultrastructural (freeze-etching technique), morphological, and biochemical effects of Sendai virus interaction with chicken erythrocytes have been studied under fusogenic (in the presence of CaCl2) and nonfusogenic (in the presence of ethyleneglycol-bis-N,N'-tetraacetic acid, [EGTA]) conditions. The following phenomena occur, irrespective of the presence of CaCl2 or EGTA: (a) binding of iodinated virus particles to chicken erythrocytes at 4 degrees C and their partial release from the cells at 37 degrees C; (b) gradual incorporation of the viral envelope and viral M-protein into plasma membrane, as visualized in the protoplasmic and exoplasmic fracture (P and E, respectively) faces of the membrane; and (c) virus-dependent transient clustering of intramembrane particles at 4 degrees C, which is reversible after transferring the cells back to 37 degrees C. The following virus-induced phenomena occur only in the presence of CaCl2: (a) rounding of cells followed by their fusion; (b) transient decrease in the density of intramembrane particles; and (c) the virus induces uptake of 45CaCl2 by chicken erythrocytes. The uptake is specific as it is inhibited by LaCl3, and no accumulation of [14C]glucose-1-phosphate ([14C]G-1-P) could be observed under the 45 CaCl2 uptake conditions. The data show that fusion of virus with plasma membrane is a Ca++-independent process and, as such, it should be distinguished from the virus-induced membrane-membrane and cell fusion processes. The latter is absolutely dependent on the rise of intracellular Ca++, as reflected by the fact that Ca++-induced rounding of chicken erythrocytes always precedes fusion (Volsky, D. and A. Loyter. 1977.Biochim. Biophys. Acta 471:253--259).

Adsorption↗
PubMed1977

Rearrangement of intramembranous particles and fusion promoted in chicken erythrocytes by intracellular Ca2+.

Ca2+ was introduced into fresh and ATP-depleted chicken erythrocytes through the aid of the inophore A23187. Intracellular Ca2+ (10-40 mM) induced fusion in ATP-depleted cells after 30-60 min incubation at 37 degrees C, but not in fresh cells. Fresh cells underwent a higher degree of haemolysis than ATP-depleted cells after accumulation of Ca2+. Uptake of Ca2+ was the same in these two systems. Intracellular Ca2+ induced rearrangement of intramembranous particles, as revealed by freeze-etching studies. The intramembranous particles in the protoplasmic face of fractured membranes obtained from fresh cells incubated with 1 mM of Ca2+ were more scattered and their density was lower than in control cells. Incubation with higher concentrations of Ca2+ (10-40 mM) induced transient changes in the intramembranous particles' density with the appearance of protrusions and depressions on the protoplasmic and exoplasmic faces of the fractured membranes, respectively. These effects were reversible upon removal of Ca2+ by washing the cells with ethyleneglycol bis(alpha-aminoethylether)-N,N'-tetraacetic acid; rearrangement of intramembranous particles was less evident after accumulation of Ca2+ in ATP-depleted cells, whose fractured membranes did not contain any protrusions or depressions. Transferring Ca2+-loaded cells to the cold caused the formation of large smooth areas devoid of intramembranous particles in the protoplasmic face of the fractured membranes. Cells containing Ca2+ appeared spherical, and removal of Ca2+ restored the normal oval shape of chicken erythrocytes.

Adenosine Triphosphate↗