bluuebunny/crossref_metadata_2025_split huggingface dataset:
Inhibition of α‐bungarotoxin binding to acetylcholine receptors by antisera from animals with experimental autoimmune myasthenia gravis
Authors: Claudio Toni , Raftery Michael A. 
Published: May 2005

AbstractConditions are described for an assay that allows the percent inhibition of α‐bungarotoxin binding to acetylcholine receptors by antisera and monovalent antigen‐binding fragments of antibody molecules (Fab) to be determined. Anti‐Torpedo californica acetylcholine‐receptor antisera, prepared in New Zealand White rabbits and Lewis rats, were tested for the ability to inhibit [125I]‐α‐bungarotoxin binding to membrane‐associated and detergent‐solubilized T californica acetylcholine receptors. Similar inhibition studies were performed using rabbit antisera and antigen‐binding fragments prepared against each of the four acetylcholine receptor subunits. Antisera and antigen‐binding fragments prepared against intact receptor could inhibit a maximum of 50% of the α‐bungarotoxin binding to solubilized receptor. The results using monovalent antigen‐binding fragments indicated that the inhibition was not due to antibody‐mediated aggregation of receptor molecules. Rabbits and rats immunized with receptor denatured by sodium dodecyl sulfate all produced antisera that could bind to nondenatured receptor, but none of these animals developed experimental autoimmune myasthenia gravis. These results suggest that the antigenic determinants present on acetylcholine receptors responsible for induction of experimental auto‐immune myasthenia gravis are lost with sodium dodecyl sulfate denaturation. A strong correlation was also observed between the presence of experimental autoimmune myasthenia gravis in rats and rabbits and the ability of the antisera from these animals to inhibit 50% of α‐bungarotoxin binding to solubilized acetylcholine receptors.
In vitro maintenance of differentiation marker synthesis by subpopulations of mouse thymocytes
Authors: Rothenberg Ellen , Triglia Dennis 
Published: May 2005

AbstractMouse thymocyte populations enriched in functionally incompetent, “immature” cells on the one hand, or in competent “mature” cells on the other hand, express different steady‐state levels of certain surface antigens and marker enzymes. In the cases of the glycoproteins H‐2 (K and D), Qa, and TL, and the DNA polymerase terminal deoxynucleotidyl transferase (TdT), these levels reflect different rates of de novo synthesis in the two populations. Thus each population appears to manifest a characteristic pattern of synthetic rates for the various products relative to total protein synthesis. To investigate the maintenance of these patterns, enriched pools of “immature” and “mature” thymocytes were incubated in vitro for 24 h, and the rates of product synthesis before and after culture were compared. H‐2 synthesis, initially most rapid in the mature cells, continued to be made at the highest rate in this population. TdT synthesis, a characteristic activity of the immature cells, was not induced in the mature cells, but proceeded at an increased relative rate in the immature population. Therefore, the differences between the rates of H‐2 and TdT synthesis were stable properties of the two thymocyte populations. Another marker of immature cells, TL, did not continue to be produced in parallel with TdT. Rather, its synthesis was selectively curtailed in relation to the continuing protein synthesis in the immature cultures. This non‐coordinate regulation of TL and TdT production in immature thymocytes may be due to several mechanisms. These are discussed with regard to their implications for pathways of thymocyte maturation.
The hatching enzyme from xenopus laevis: Limited proteolysis of the fertilization envelope
Authors: Urch Umbert A. , Hedrick Jerry L. 
Published: May 2005

AbstractHatching in the amphibian Xenopus laevis involves release of an embryo‐secreted hatching enzyme, a protease, which weakens the envelope surrounding the embryo. The envelope is not totally solubilized, which infers that only selected envelope components are hydrolyzed by the enzyme. The susceptibility of the glycoprotein components composing the envelope to hydrolysis by the hatching enzyme was investigated. Isolated envelopes in various physical states, ie, particulate and solubilized, were treated with the hatching enzyme, and the resulting envelope hydrolysis products were characterized by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The susceptibility of the envelope components to proteolysis was not a function of the state of the envelope. The envelope components most susceptible to proteolysis were the 125K and 11 8K components followed by the 60K and 71 – 77K components. These components are minor constituents of the envelope. The major constituents, 33K and 40K, were relatively resistant to hydrolysis by the hatching enzyme. From these observations, we infer that the envelope components hydrolyzed are components that link or bind together the major structural elements of the envelope, eg, the 33K and 40K components. Selective destruction of the components required for maintaining the structural integrity of the envelope, eg, the “nuts and bolts” of the structure, permits a weakening of the envelope that allows the embryo to hatch without having to destroy totally (hydrolyze) the envelope.
Effect of exogenous fatty acids on growth, membrane fluidity, and phospholipid fatty acid composition in yeast
Authors: Esfahani Mojtaba , Kucirka Elise M. , Timmons Frank X. , Tyagi Somdev , Lord Arthur E. , Henry Susan A. 
Published: May 2005

AbstractThe growth response of a double‐mutant fatty acid auxotroph of yeast Saccharomyces cerevisiae to exogenous saturated fatty acids of a homologous series from 12:0 to 16:0, each supplied with oleate, linoleate, linolenate, or cis‐Δ11‐ eicosenoate, cannot be explained in terms of the efficiency of incorporation of the fatty acids into phospholipids or alteration of membrane fluidity. There is, however, a negative correlation between growth and levels of 12:0 plus 13:0 in phospholipids, as well as a positive correlation between growth and levels of 14:0, 1 5:0, and 1 6:0. We, therefore, conclude that the predominant factor in these phospholipid fatty acyl chain modifications is maintenance of an optimal concentration of C14:0 through C16:0 in phospholipids of this organism.
The effects of dipalmitoyl phosphatidyl choline on the precipitation of native fibrils and segment‐long‐spacing aggregates from collagen solution
Authors: McKenzie James C. , Belton John C. , Klein Robert M. 
Published: May 2005

AbstractThe effect of dipalmitoyl phosphatidyl choline (DPPC), the major phospholipid component of pulmonary surfactant, on the precipitation of collagen in the form of native fibrils and segment‐long‐spacing (SLS) aggregates was studied in vitro. The effects of DPPC on both phases of collagen fibrillogenesis were analyzed spectrophotometrically, and alterations in the morphology of precipitated fibrils and SLS aggregates were ascertained by transmission electron microscopy (TEM). Low concentrations of DPPC inhibited the growth phase of fibrillogenesis, while higher concentrations were required to inhibit nucleation. Both the meshwork density and mean width of precipitated fibrils were altered by DPPC, as was the size of SLS aggregates. Segment‐long‐spacing aggregates prepared from pepsin‐treated collagen were inhibited to a greater degree than SLS aggregates prepared from untreated collagen, indicating that the pepsin‐susceptible residues of the telopeptide extensions of tropocollagen molecules stabilize SLS aggregates against the effects of DPPC. Based on these results and the inhibition of the growth phase at lower concentrations than those which inhibited the nucleation phase of fibrillogenesis, it was concluded that the primary mechanism of DPPC inhibition is electrostatic interference between the positively charged phospholipid molecules and the net positive charge of collagen. It is proposed that pathological conditions involving the pulmonary epithelium may allow interaction between surfactant and collagen, which could further weaken the interstitial connective tissue.
Protease‐insensitive sea urchin embryo cell adhesions become protease sensitive in the presence of azide or cytochalasin B
Authors: Bertolini Donald R. , Watanabe Michiko , Turner Robert S. 
Published: May 2005

AbstractTo understand the nature of the cell adhesions that must be modified during sea urchin embryo primary mesenchyme formation, we are studying the adhesive components of the hatched blastula stage embryo of Strongylocentrotus purpuratus. Pronase treatment conditions have been defined that leave the cells intact and able to recover from the effects of the protease upon its removal. Under these conditions, adhesion of the cells to tissue culture plates is totally eliminated, but cell‐cell adhesion formation is only partially inhibited. Analysis of iodinated cell surface proteins indicates that most are affected by thepronase. Further studies of pronase effects found that sodium azide‐treated cells are slightly adhesive and that pronase treatment of azidc‐treated cells totally eliminates cell‐cell adhesions.
Phosphoproteins in dictyostelium discoideum
Authors: Coffman D. S. , Leichtling Ben H. , Rickenberg H. V. 
Published: May 2005

AbstractThe phosphoproteins of Dictyostelium discoideum were compared at different stages of development by polyacrylamide gel electrophoresis. Certain phosphoproteins of vegetative amoebae were conserved while others appeared and disappeared during development. Four major phosphoproteins with apparent subunit molecular weights of 50,000, 47,000, 38,000, and 34,000 disappeared precociously in response to exogenous cAMP. Two membranal phosphoproteins, with apparent subunit molecular weights of 80,000 and 81,000, appeared precociously in response to added cAMP. One of these phosphoproteins, molecular weight of 80,000, has been identified tentatively as the “contact site A” glycoprotein. Another membranal protein, with apparent subunit molecular weight of 42,000, unaffected in its appearance by cAMP, has been identified tentatively as phosphoactin.
Isolation of a high molecular weight glycoconjugate derived from the surface of S purpuratus eggs that is implicated in sperm adhesion
Authors: Glabe Charles G. , Lennarz William J. 
Published: May 2005

AbstractSea urchin sperm–egg adhesion is mediated by bindin, a sperm surface protein that has lectin‐like activity. Bindin agglutinates eggs, and this interaction has been shown to be inhibited by glycopeptides released from the egg surface by protease treatment. In this study, we report the purification and properties of such an egg surface glycoconjugate that may be involved in sperm adhesion. The glycoconjugate was partially purified by gel filtration and affinity chromatography on bindin particles. Upon gel filtration on Sepharose CL 4‐B, the glycoconjugate elutes near the void volume, suggesting that it has a molecular weight in excess of one million. In addition, we have found that the egg surface glycoconjugate agglutinates bindin particles, indicating that it is multivalent. Carbohydrate analysis indicates that the glycoconjugate is composed primarily of fucosc, xylose, galactose, and glucose. This purified egg surface component is the most potent inhibitor of bindin‐mediated egg agglutination yet described.
Microfilament reorganization in normal and cytochalasin B treated adherent thrombocytes
Authors: Taylor Richard G. , Lewis Jon C. 
Published: May 2005

AbstractThrombocyte adhesion following activation by a Formvar surface involves a morphologic transition resulting in a fully spread cell. Correlative SEM and whole mount TEM were used to study the cytoskeletal alterations that accompany changes in surface morphology during adhesion. Following initial adhesion, thrombocytes extend slender pseudopods containing longitudinally oriented bundles of filaments that are 13–22 nm in diameter. Concomitant with pseudopod extension, a cytoplasmic hyalomere, consisting of a dense filamentous network, extends between the pseudopods and ultimately results in a fully spread cell. Treatment of thromboyctes with cytochalasin B (10−5 M) caused clumping of the hyalomere filament network and retraction of the hyalomere. Examination of partially retracted cells revealed that pseudopod filament bundles were continuous with the contracting filamentous network. It is concluded that pseudopod filament bundles and cytoplasmic hyalomere filaments are interconvertible and that their organizational relationship changes in accordance with gross morphologic changes.
The dynamic state of liver gap junctions
Authors: Yancey S. Barbara , Nicholson Bruce J. , Revel Jean‐Paul 
Published: May 2005

AbstractBy the use of a simple, rapid method for the isolation of gap junctions from small amounts of rat liver (2–3 g), we have followed the incorporation of the radiolabeled amino acid precursors 3H‐leucine and 35S‐methionine into the gap junction protein. In timed studies with 35S‐methionine as precursor, the specific activity in the protein is maximal by 4 h after a single injection of 300 μCi/100 g body weight. From the decay in the specific activity with time after a single injection, the gap junction protein has an apparent half‐life of about 19 h. Because of problems of reutilization of radiolabeled amino acid with 35S‐methionine as precursor, this apparent halflife probably overestimates the true half‐life and indicates a surprisingly rapid turnover of the gap junction protein. This short half‐life suggests that, in rat liver, the gap junctions may be very responsive to alterations in physiological demands.
An immunochemical approach for the analysis of membrane protein alterations in Ca2+‐loaded human erythrocytes
Authors: Bjerrum O.J. , Hawkins M. , Swanson P. , Griffin M. , Lorand L. 
Published: May 2005

AbstractAn increase in the intracellular concentration of Ca2+ in human erythrocytes results in the formation of γ‐glutamyl‐ϵ‐lysine cross‐linked membrane protein polymers. Following solubilization of the membranes with SDS, these polymers can be isolated on a Lubrol‐containing sucrose gradient. Immunoelectrophoresis of the polymeric material with a polyspecific rabbit antibody against human ghosts gave rise to a single, but heterogeneous, precipitate. The polymer was amphiphilic and, on addition to Triton‐solubilized erythrocyte membrane proteins, it coprecipitated with spectrin. When the antighost antibody was absorbed with the polymer prior to cross immunoelectrophoresis of normal erythrocyte membrane proteins, the precipitates of glycophorin, acetylcholinesterase, and hemoglobin were normal, whereas the anti‐body liters against band 3 protein, spectrin, and ankyrin became reduced. Furthermore, a rabbit antibody raised against the isolated human polymer reacted selectively with the same three membrane proteins. No reactions occurred with lysate proteins.
Modulation of one of three murine bone marrow stromal cell lines to adipose cells by serum and insulin
Authors: Anderson R.W. , Mann S.L. , Crouse D.A. , Sharp J.G. 
Published: May 2005

AbstractAdipose cells have been recognized as an integral component of the bone marrow hematopoietic microenvironment in vivo and as an essential cell type required for in vitro maintenance of stem cells. Four stromal cell lines obtained from the adherent cell population of murine bone marrow cultures have been enriched and purified by multiple trypsinizations. We noted that these cell lines exhibited an accumulation of vacuoles of lipid, the extent of which varied be‐tween cell lines in response to a change from medium containing 10% fetal calf serum to medium containing 20% horse serum. The lipid was lost when the cell lines were transferred back into the medium supplemented with fetal calf serum. In light of the reported lipogenic and antilipolytic effects of insulin on fibroblasts and adipocytes, we investigated the ability of insulin to induce adipocyte transformation of these bone marrow stromal cell populations. Three cell lines were exposed to bovine insulin at concentrations ranging from 10−9 to 10−6 M. All three cell lines responded to the insulin by accumulating lipid, but the extent of accumulation and the insulin concentration at which maximum lipid content was attained were population specific. One cell line (MC1) responded fully at physiological levels of insulin (10−9 M), whereas the other two showed lipid accumulation only at pharmacological concentrations. The initial growth of MC1 was inhibited in the presence of 10−9 M insulin which is compatible with the observed differentiation to adipocytes. The growth of MC3 was unaltered in the presence of physiological concentrations of insulin, whereas that of MC4 was accelerated. Grafts of organ cultures of the cell lines under the kidney capsule of syngeneic mice developed specific characteristics rep‐resentative of the different cell lines. In particular, the majority of the grafts of MC1 consisted primarily of fat cells which were not observed in the grafts of MC3 and MC4. These data strongly suggest that these cell lines comprise cells with different potentialities and that the MC1 line represents a preadipocyte stromal cell of bone marrow.
Neuronal differentiation in cultures of weaver (wv) mutant mouse cerebellum
Authors: Willinger Marian , Margolis David M. , Sidman Richard L. 
Published: May 2005

AbstractIn the present study we report for the first time a weaver (wv) gene dose effect on neuron survival and neurite formation in vitro. Dissociated cerebellar cells from postnatal 7‐ and 8‐day‐old normal ( + / + ), heterozygous weaver ( + /wv) and homozygous weaver (wv/wv) mice were cultured as monolayers on poly‐L‐lysine coated glass. Cell death occurred rapidly in wv/wv cultures. Cell counts showed that less than 20% of the total neurons and neuronal precursors (identified by “birthday” radiolabeling techniques) survived by Day 3. Cell death was less extensive in + /wv cultures with 65% of the total neurons and 80% of the precursors surviving by Day 3. In contrast to wv/wv cultures, younger neurons survive better than the total population in + /wv cultures. The impairment of neurite formation over the first week is also proportional to the number of mutant genes as shown by quantitation of (a) the percentage of cells with neurites; (b) the percentage of cells with neurites of a given length class with time; (c) the lengths of the longest processes formed per cell. The mean longest neurite lengths obtained by computer digitization at 6 days in vitro were 41.8, 26.8, and 9.0 μm for + / +, + /wv, and wv/wv granule cells, respectively.
Unscheduled synthesis of DNA and poly(ADP‐ribose) in human fibroblasts following DNA damage
Authors: McCurry Lynette Salter , Jacobson Myron K. 
Published: May 2005

AbstractUnscheduled DNA synthesis has been measured in human fibroblasts under conditons of reduced rates of conversion of NAD to poly(ADP‐ribose). Cells heterozygous for the xeroderma pigmentosum genotype showed normal rates of UV induced unscheduled DNA synthesis under conditions in which the rate of poly(ADP‐ribose) synthesis was one‐half the rate of normal cells. The addition of theophylline, a potent inhibitor of poly(ADP‐ribose) polymerase, to the culture medium of normal cells blocked over 90% of the conversion of NAD to poly(ADP‐ribose) following treatment with UV or N‐methyl‐N′‐nitro‐N‐nitro‐soguanidine but did not affect the rate of unscheduled DNA synthesis.
Quantitation of changes in cell surface determinants during skeletal muscle cell differentiation using monospecific antibody
Authors: Grove Barbara Kay , Schwartz Gary , Stockdale Frank E. 
Published: May 2005

AbstractThe differentiation of skeletal muscle is characterized by recognition, alignment, and subsequent fusion of myoblast cells at their surfaces to form large, multinucleated myotubes. Monoclonal antibodies were used to investigate anti‐genie changes in the cell surface membrane specific for various stages of myogenesis. Chick embryonic skeletal muscle cells were cultured in vitro to the desired stage of differentiation and then injected into BALB/c mice. Spleen cells from the immunized mice were hybridized with NS‐1 or P3 8653 mouse myeloma cells. Hybrid cell clones were selected in HAT medium and screened using an indirect radioimmunoassay for the production of monoclonal antibodies specific to myogenic cell surfaces. Target cells for the radioimmunoassay included three stages of myogenesis (myoblasts, midfusion myoblasts, and myotubes) and chick lung cells as a control for polymorphic antigens. Sixty‐one clones were obtained which produced antibodies specific for myogenic cells. Thirty‐five of these clones were generated from mice immunized with midfusion myoblast stages of myogenesis and 26 were obtained from mice immunized with the later myotube stage of myogenesis. Quantitative measurements by RIA of myogenic determinants per cell surface area on each target cell type revealed that most of the determinants decrease during myogenesis when midfusion myoblasts are used as the immunogen. When myotube stages are used as the immunogen, more determinants increase with cell differentiation. Therefore, the most common pattern of determinant change is for them to be present at all stages of myogenesis but to vary quantitively through development. There are determinants unique to each stage of myogenesis and marked quantitative differences within a cell stage for each determinant.
Structural analysis of fibronectin with monoclonal antibodies
Authors: Atherton Blair T. , Taylor Deena M. , Hynes Richard O. 
Published: May 2005

AbstractThe reactivity of six monoclonal antibodies with fragments of fibronectin produced with trypsin, chymotrypsin, and Staphylococcus aureus V8 protease is described. All these antibodies reacted with fragments derived from the C‐terminal one‐third of fibronectin. This region probably contains sites for the binding of fibronectin to cells, and to heparin and may also contain active sites for the reattachment, spreading, and alignment of transformed cells. Analysis of the reactivities of different sets of proteolytic fragments with the antibodies and with other ligands (eg. heparin) allows one to determine overlaps between the fragments and to locate the positions of the different binding sites for antibodies and ligands. One of the antibodies has allowed us to identify a site of structural difference between cellular and plasma fibronectins from hamsters. The site recognized by this antibody is located near to, but not at, the C‐terminal end and docs not involve carbohydrate groups. Because of its internal location in fibronectin, this difference suggests that there are probably different genes for cellular and plasma fibronectin. These monoclonal antibodies should be useful for further probing the functions present in the C‐terminal regions of fibronectin and for determining their locations.