bluuebunny/crossref_metadata_2025_split huggingface dataset:
Properties of (Mg2+ + Ca2+)‐ATPase of erythrocyte membranes prepared by different procedures: Influence of Mg2+, Ca2+, ATP, and protein activator
Authors: Katz Sidney , Roufogalis Basil D. , Landman Amiram D. , Ho Larry 
Published: May 2005

AbstractErythrocyte membranes prepared by three different procedures showed (Mg2+ + Ca2+)‐ATPase activities differing in specific activity and in affinity for Ca2+. The (Mg2+ + Ca2+)‐ATPase activity of the three preparations was stimulated to different extents by a Ca2+‐dependent protein activator isolated from hemolystes. The Ca2+ affinity of the two most active preparations was decreased as the ATP concentration in the assay medium was increased. Lowering the ATP concentration from 2 mM to 2–200 μM or lowering the Mg:ATP ratio to less than one shifted the (Mg2+ + Ca2+)‐ATPase activity in stepwise hemolysis membranes from mixed “high” and “low” affinity to a single high Ca2+ affinity. Membranes from which soluble proteins were extracted by EDTA (0.1 mM) in low ionic strengh, or membranes prepared by the EDTA (1–10 mM) procedure, did not undergo the shift in the Ca2+ affinity with changes in ATP and MgCl2 concentrations. The EDTA‐wash membranes were only weakly activated by the protein activator. It is suggested that the differences in properties of the (Mg2+ + Ca2+)‐ATPase prepared by these three procedures reflect differences determined in part by the degree of association of the membrane with a soluble protein activator and changes in the state of the enzyme to a less activatable form.
Characterization of antigenic sialoglycoprotein subunits of the placental brush border membranes: Comparison with liver and kidney membrane subunits by two‐dimensional electrophoresis
Authors: Wada H. Garrett , Hass Philip E. , Sussman Howard H. 
Published: May 2005

AbstractThe sialoglycoprotein subunits of human placental brush border membranes were labeled by sequential treatment with periodate and (3H)‐sodium borohydride, which trititates sialic acid, and by lactoperoxidase‐catalyzed (125I) iodination of tyrosine residues. The labeled subunits were characterized with respect to their affinity for antisera raised against Triton X‐100 extracts of placental brush border membranes. The immunochemically reactive components were analyzed by two‐dimensional electrophoresis according to a modification of the O'Farrell technique [20] enabling the assignment of estimated Mr̄ and pI. Of the 33 3H‐labeled brush border subunits present in Triton X‐100‐solubilized membrane preparations, 18 subunits reacted with antiplacental brush border antisera insolubilized on CNBr‐activated Sepharose or in immunoprecipitates. Fourteen of these tritiated subunits were also labeled with 125I, confirming that these are glycoproteins.The plasma membranes of normal human liver and microsomes from kidney were examined for the placental brush border glycoprotein subunits by reaction with insolubilized antiplacental brush border antisera and two‐dimensional electrophoresis of the reacting tritium‐labeled subunits. Comparison of the two‐dimensional electrophoretic maps of the immunochemically reacting glycoproteins from liver, kidney, and placenta resulted in the identification of seven placental subunits in common with liver and kidney on the basis of antigenic cross‐reactivity, Mr̄, and pI. Four placental glycoproteins were not found in the other tissues and are potentially specific to the placenta. Three of the placental subunits were only seen in placenta and kidney. Three of the subunits ran at the dye front and could not be assigned molecular weights. One of the subunits was poorly labeled by tritiation of sialic acid and was not considered.
Regulation of the cell cycle of 3T3 cells in culture by a surface membrane‐enriched cell fraction
Authors: Whittenberger Brock , Raben Daniel , Glaser Luis 
Published: May 2005

AbstractAddition of a suspension of a surface membrane enriched fraction prepared from confluent 3T3 cells to sparse 3T3 cells in culture results in a concentration dependent and saturable decrease in the rate of DNA synthesis. The inhibition of cell growth by membranes resembles the inhibition of cell growth observed at confluent cell densities by a number of criteria: (1) In both cases the cells are arrested in the G1 protion of the cell cycle; (2) the inhibition by membranes or by high local cell density can to a large extent be compensated for by raising the serum concentration or by addition of fibroblast growth factor plus dexamethasone. Membranes prepared from sparse cultures inhibit less well than membranes from confluent cultures in a manner which suggests that binding of membranes to cells is not by itself sufficient to cause inhibition of cell growth. The inhibitory activity has a subcellular distribution similar to phosphodiesterase (a plasma membrane marker) and appears to reside in one or more intrinsic membrane components. Maximally, membranes can arrest about 40% of the cell population in each cell cycle. Plasma membranes obtained from sparse 3T3 cells are less inhibitory than membranes obtained from confluent cells. This suggests either that the inhibitory component(s) in the plasma membrane responsible for growth inhibition may be in part induced by high cell density, or that this component(s) may be lost from these membranes during purification.
Structure of functional a salina – E Coli hybrid ribosome by electron microscopy
Authors: Boublik M. , Wydro R. M. , Hellmann W. , Jenkins F. 
Published: May 2005

AbstractSmall 40S Artemia salina and large 50S Escherichia coli ribosomal subunits can be assembled into 73S hybrid monosomes active in model assays for protein synthesis. The reciprocal combination–small 30S E coli and large 60S A salina–fails to form hybrids. The 73S hybrid particles strongly resemble homologous 70S E coli and 80S A salina monosomes. The morphologic differences between the corresponding eukaryotic and prokaryotic ribosomal particles, established by electron microscopy, do not significantly affect the assembly and mutual orientation of 40S A salina and 50S E coli subunits in the heterologous monosome. The fact that the structure of the interface, the supposed site of protein synthesis, is preserved in the active hybrid implies that retention or loss of biologic activity of hybrid ribosomes is determined by the extent of conformational changes in the interface.
The accessibility of antigenic determinants of ribosomal protein s4 in situ
Authors: Winkelmann Donald , Kahan Lawrence 
Published: May 2005

AbstractAntibodies to Escherichia coli ribosomal protein S4 react with S4 in subribosomal particles, eg, the complex of 16S RNA with S4, S7, S8, S15, S16, S17, and S19 and the RI* reconstitution intermediate, but they do not react with intact 30S subunits. Antibodies were isolated by three different methods from antisera obtained during the immunization of eight rabbits. Some of these antibody preparations, which contained contaminant antibodies directed against other ribosomal proteins, reacted with subunits, but this reaction was not affected by removal of the anti‐S4 antibody population. Other antibody preparations did not react with subunits. It is concluded that the antigenic determinants of S4 are accessible in some protein deficient subribosomal particles but not in intact 30S subunits.
Extracellular lectin and its glycosaminoglycan inhibitor in chick muscle cultures
Authors: Ceri Howard , Shadle Paula J. , Kobiler David , Barondes Samuel H. 
Published: May 2005

AbstractEmbryonic chick muscle contains two developmentally regulated lectins, which may be involved in cell interactions. These endogenous lectins are assayed as agglutinins of appropriate test erythrocytes. One of these, called lectin‐2, interacts with specific glycosaminoglycans, especially heparin and dermatan sulfate. Lectin‐2 is present at constant levels in both chick fibroblast and chick muscle cells throughout 14 days of culture but is released into the medium of cultured embryonic muscle after 7‐8 days of culture, soon after myoblast fusion. Lectin‐2 interacts strongly with a component of substrate‐attached material in embryonic muscle cultures which is extractable from the culture dishes with alkali after the cells have been removed with ethylediaminetetraacetic acid. The active component in the substrate‐attached material appears to be a glycosaminoglycan that is a more potent inhibitor of lectin‐2 agglutination activity than any of the known glycosaminoglycans that we have tested. The active material is degraded by chondroitinase ABC but not by chondrotinase AC, hyaluronidase, or proteolytic enzymes and thus appears to be similar to dermatan sulfate. The results of these studies raise the possibility that lectin‐2 functions by interacting with glycosaminoglycans, either associated with the cell surface or with the extracellular matrix.
Cellular and metabolic specificity in the interaction of adhesion proteins with collagen and with cells
Authors: Kleinman H. K. , Hewitt A. T. , Murray J. C. , Liotta L. A. , Rennard S. I. , Pennypacker J. P. , McGoodwin E. B. , Martin G. R. , Fishman P. H. 
Published: May 2005

AbstractFibronectin mediates the adhesion of fibroblasts to collagen substrates, binding first to the collagen and then to the cells. We report here that the interaction of the cells with the fibronectin‐collagen complex is blocked by specific gangliosides, GD1 a and GT1, and that the sugar moieties of these gangliosides contain the inhibitory activity. The gangliosides act by binding to fibronectin, suggesting that they may be the cell surface receptor for fibronectin. Evidence is presented that other adhesion proteins or mechanisms of attachment exist for chondrocytes, epidermal cells, and transformed tumorigenic cells, since adhesion of these cells is not stimulated by fibronectin. Chondrocytes adhere via a serum factor that is more temperature‐sensitive and less basic than fibronectin. Unlike that of fibroblasts chondrocyte adhesion is stimulated by low levels of gangliosides. Epidermal cells adhere preferentially to type IV (basement membrane) collagen but at a much slower rate than fibroblasts or chondrocytes. This suggests that these epidermal cells synthesize their own specific adhesion factor. Metastatic cells cultured from the T241 fibrosarcoma adhere rapidly to type IV collagen in the absence of fibronectin and do not synthesize significant amounts of collagen or fibronectin. Their growth, in contrast to that of normal fibroblasts, is unaffected by a specific inhibitor of collagen synthesis. These data indicate the importance of specific collagens and adhesion proteins in the adhesion of certain cells and suggest that a reduction in the synthesis of collagen and of fibronectin is related to some of the abnormalities observed in transformed cells.
Cell surface fibronectin and oncogenic transformation
Authors: Hynes Richard O. , Destree Antonia T. , Perkins Margaret E. , Wagner Denisa D. 
Published: May 2005

AbstractFibronectin is a large glycoprotein at the cell surface of many different cell types; a related protein is present in plasma. Fibronectin is a dimer of 230,000‐dalton subunits and also occurs in larger aggregates; it forms fibrillar networks at the cell surface, between cells and substrata and between adjacent cells, and it is not a typical membrane protein. Cell surface fibronectin is reduced in amount or absent on transformed cells and in many cases its loss correlates with acquisition of tumorigenicity and, in particular, metastatic ability. Exceptions to the correlations with transformation and tumorigenicity exist. Loss of fibronectin and the resulting reduced adhesion appear to be involved in pleiotrpoic alterations in cell behavior and may be responsible for several aspects of the transformed phenotype in vitro. Fibronectin interacts with other macromolecules (collagen/gelatin, fibrin/fibrinogen, proteoglycans) and is apparently connected to microfilaments inside the cell.
Tumor metastases and cell‐mediated immunity in a model system in DBA/2 mice. VIII. Expression and shedding of Fcγ receptors on metastatic tumor cell variants
Authors: Schirrmacher Volker , Jacobs Wolfgang 
Published: May 2005

AbstractThe expression of receptors for the Fc portion of IgG immunoglobin molecules was studied on tumor cell lines with high and low metastatic capacity. Two tumor cell lines from DBA/2 mice that had high metastatic activity, ESb and MDAY‐D2, contained a high percentage of Fc receptor positive cells, as detected in a rosette assay with IgG antibody‐coated erythrocytes (EA). In contrast, the low metastatic parental line Eb, from which ESb was derived, contained only a low percentage of EA‐rosette‐forming cells. ESb ascites tumor cells adapted to tissue culture in the presence of 2‐mercaptoethanol (2ME) had a high expression of Fc receptors, whereas a cell line adapted to tissue culture in the absence of 2ME had a low expression of Fc receptors.“Soluble” Fc receptors were detectable by their ability to bind to EA and to cause blocking of rosette formation. They were found to be present in fluids from tumor‐bearing animals, such as serum and cell‐free ascites. Even animals with an ascites tumor of the low‐metastatic line Eb contained “soluble” Fc receptors.The results are discussed with regard to their possible significance for tumor metastasis.
The serum‐free growth of Balb/c 3T3 cells in medium supplemented with bovine colostrum
Authors: Klagsbrun M. , Neumann J. 
Published: May 2005

AbstractBovine milk contains growth promoting factors that stimulate DNA synthesis and cell division in confluent monolayers of quiescent Balb/c 3T3 cells. The growth factor activity was highest in colostrum obtained within 24 hours after birth of a calf. Samples of milk obtained 32 hours and 60 hours after birth were 20% and 1% as active respectively as was a sample obtained 8 hours after birth in stimulating DNA synthesis. No activity was detectable 3 days after birth or thereafter. A similar temporal dependence was found in sheep's milk. Bovine colostrum obtained on the day of a calf's birth can be substituted for serum and will support the growth of sparse Balb/c 3T3 cells to confluence. In Dulbecco's modified Eagle's medium (DMEM) supplemented with 2.5% (vol/vol) bovine colostrum, the number of Balb/c 3T3 cells in a dish increased 35‐fold, from 2.0 × 104 cells to 7 × 105 cells. The generation time was approximately 38 hours. Proliferation of cells was characterized by formation of clusters of confluent Balb/c 3T3 cells which were smaller in size and more tightly packed than were Balb/c 3T3 cells grown to confluence in serum. No proliferation was detected in DMEM supplemented with milk obtained 10 days after birth of a calf or in DMEM supplemented with bovine serum albumen.
Structural states of dictyostelium myosin
Authors: Stewart Peter R. , Spudich James A. 
Published: May 2005

AbstractMyosin purified from Dictyostelium amoebae has approximately 10% by weight of RNA associated with it, unless specific steps (DEAE cellulose chromatography or R Nase digestion) are taken to remove it. This RNA has significant effects on the structural states formed by the myosin at low ionic strength in the presence of Mg2+.Rapid precipitation of Rna‐free myosin by dilution generates bipolar thick filaments (540 nm long, 33 nm thick), often with a bare zone and a 15‐nm transverse repeat. Rapid precipitation of myosin with copurified RNA yields linear aggregates of bipolar filaments, showing some lateral association.Slow precipitation of RNA‐free myosin by dialysis yields very long filaments or ribbons (>5 μm, 30–60 nm wide) in which the myosin may be packed diagonally across the filament, similar to the “side‐polar” aggregates formed by other nonmuscle myosins and by smooth muscle myosin (Craig R, Megerman J: J Cell Biol 75:990, 1977; Hinssen H, D'Haese J, Small JV, Sobieszek A: J Ultrastruct Res 64:282, 1978). Slow precipitation of myosin with copurified RNA generates linear filaments with repeat intervals of 290 and 650 nm.Other polyanions were tested for their effects on myosin aggregation. Total RNA and ribosomal RNA from Dictyostelium, when added to RNA‐free myosin, also induced the extensive linear aggregation seen with the copurified RNA/myosin complex, although higher concentrations of RNA were required to obtain quantitatively the same effect. DNA and heparin were also effective inducers of linear aggregation, whereas homopolymers of nucleotides and of acidic or basic amino acids were poorly effective.
Effects of the tumor promoter TPA on the induction of DNA synthesis in normal and RSV‐transformed rat fibroblasts
Authors: Magun Bruce E. , Bowden G. T. 
Published: May 2005

AbstractInduction of DNA synthesis by the tumor promoter tetradecanoyl phorbol acetate (TPA) was studied in a line of cultured rat fibroblasts (Rat‐1) and their ffRous sarcoma virus‐transformed derivative (Rat‐1(RSV)). Following serum deprivation for 54 h to achieve quiescene, semiconservative DNA replication was measured by incubation of cells in BrdUrd and FdUrd after serum stimulation in the presence or absence of TPA. Optimal concentrations of TPA (0.1–0.5 μg/ ml) in serum‐free medium induced a small increase (10–15%) in the amount of DNA made over a 30‐h period in both Rat‐1 and Rat‐1 (RSV) cells. When Rat‐1 cells were stimulated by a 4‐h serum pulse, 30% of the DNA was replicated by 30 h. If the serum pulse was follwed by TPA addition, 702% DNA replication wass observed. If the serum pulse was preceded by TPA addition, the onset of DNA synthesis waas delayed by several hous, but stimulation of DNA synthesis occurred. In contrast, the Rat‐1 (RSV) cells did not show an increase in DNA synthesis induced by TPA in similar protocols, but the serum‐induced onset on DNA synthesis was delayed by several hours in the presence of TPA. Therefore, TPA acts as a co‐inducer of DNA synthesis in the Rat‐1 but not in the Rat‐(RSV) cells. The parent alcohol, phorbol, was inactive in Rat‐1 cells, but delayed the onset of DNA synthesis in the Rat(RSV) cells. We conclude that the co‐inducing and delaying activities of TPA on DNA synthesis appear to be distinct and to act at different points in the G1 phase of the cell cycle.
Analysis of cell surface interactions by measurements of lateral mobility
Authors: Elson Elliot L. , Reidler Jeffry A. 
Published: May 2005

AbstractInteractions of cell surface components with one another and with structures inside and outside the cell may have important physiological functions in the transmission of signals and the assembly of specialized structures. These interactions may be detected and analyzed through their effects on the lateral mobility of cell surface molecules. Measurements by a fluorescence photobleaching method have shown that in general lipid‐like molecules diffuse rapidly and freely through the plasma membrane, whereas proteins move much more slowly or appear to be immobile. This dichotomy has been supposed to result from forces beyond the viscosity of the lipid bilayer, which specifically retard the diffusion of membrane proteins. This general picture should be qualified, however, by noting that the lateral mobility of lipid‐like molecules can be influenced in detail by changes in the state of the plasma membrane such as result from mitosis or fertilization. The interactions of cell surface proteins that limit their lateral mobility are unknown. The effects of binding concanavalin A to localized regions of cell surface show that these interactions can vary in subtle and complex ways. It may soon be useful to interpret mobility experiments in terms of simple reaction models that attempt to describe surface interactions in physicochemical terms. More experimental data are needed to carry out this program and to relate interactions that affect mobility to the structural connections between cell surface components and the cytoskeleton, which have been detected by biochemical methods and electron and immunofluorescence microscopy.
A comparative dielectric study of human serum low density lipoprotein before and after partial digestion by trypsin
Authors: Chana G. S. , Chapman M. J. , Sheppard R. J. , Mills G. L. , Goldstein Sonia , Grant E. H. 
Published: May 2005

AbstractThe relative permittivity of aqueous solutions of human serum low density lipoprotein (LDL) and partially trypsin digested lipoprotein (T‐LDL) has been determined for various concentrations at 20°C over the frequency range 0.15–100 MHz. Comparison of the dielectric dispersion curves for the digested lipoprotein with those for the native preparation revealed a larger low‐frequency dielectric increment, which may be attributed to an increase in the number of counterions moving over the surface of the molecule. An explanation of this observation is an elevation of 70% in the net negative charge on the surface of the trypsin‐treated particle as compared to its native counterpart.
The role of the Escherichia coli λ receptor in the transport of maltose and maltodextrins
Authors: Ferenci Thomas , Boos Winfried 
Published: May 2005

AbstractThe λ receptor is a peptidoglycan‐associated integral protein that spans the outer membrane. Beside its function in phage λ adsorption it participates in transport. The latter function can be summarized as follows: (1) Receptor allows the nonspecific permeation of small molecules other than maltose and maltodextrins (in close analogy to a molecular sieve). Here the only criterion for selectivity is size and it has the properties of an unspecific pore. In this respect, it is similar to the outer membrane proteins Ia, Ib, and Ic, the porins. (2) It is a binding protein for maltodextrins. Binding affinity is low but increases by a factor of 500 as the chain length of the maltodextrins increases. In contrast, the affinity of the periplasmic maltose‐binding protein for maltose and maltodextrins is similarly high (in the μM range). (3) In the in vitro system of liposomes, the λ receptor facilitates specifically the diffusion of maltodextrins that exceed the size limit given by its porin function. This clearly demonstrates that the λ receptor alone is able to specifically overcome the permeability barrier of the outer membrane for maltodextrins. (4) From the genetic and kinetic analysis of maltose and maltodextrin transport, it can be concluded that the λ receptor interacts with the periplasmic maltose‐binding protein. (5) Electron microscopic studies indicate a location for the maltose‐binding protein in the outer cell envelope. This location is dependent on the presence of the λ receptor.
Interleukin 2 in cell‐mediated immune responses
Authors: Paetkau Verner , Shaw Jennifer , Caplan Barry , Mills Gordon B. , Lee Kwok‐Choy 
Published: May 2005

AbstractThe lymphokine Interleukin 2 (IL2) restores T cell responses in a number of in vitro systems where immunogenicity has been compromised. UV irradiation of the stimulating allogeneic cells in a mixed leukocyte culture eliminates the production of cytotoxic T lymphocytes and greatly reduces the DNA synthesis response. IL2 restores both parameters. UV‐irradiated stimulators are also unable to induce the normal production of IL2 which is observed in a mixed leukocyte culture. The cytotoxic activity of allogeneically stimulated thymocytes is almost completely lost within 24 hours after removal of IL2 at 5 days, indicating that the lymphokine is continuously required to maintain CTL. Thymocytes in 4‐day cultures do not adsorb IL2 unless they are simultaneously activated with a mitogen. Finally, IL2 does not adequately restore a secondary response to the purified protein derivative of tuberculin (PPD) in adherent‐cell‐depleted cultures, indicating that macrophages, in addition to being required for IL2 production, have other functions. These probably include the presentation of soluble antigens to responding cells.