bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cholera toxin‐catalysed ADP‐ribosylation of erythrocyte proteins: General properties
Authors: Gill D. Michael 
Published: May 2005

AbstractUpon incubation of lysed pigeon erythrocytes with NAD, adenosine diphosphateribose (ADP‐ribose) is incorporated into nuclear poly ADP‐ribose and into an unidentified acid‐insoluble product of the cytosol. The properties of these incorporations have been examined and a method developed for reducing their amount whilst retaining the sensitivity of the lysate to cholera toxin. This method has allowed the detection and description of a set of cholera toxin‐specific ADP‐ribose transfers to membrane‐bound and soluble proteins under conditions that lead to adenylate cyclase activation.
Lipid‐protein interactions in membranes: Effect of lipid composition on mobility of spin‐labeled cysteine residues in yeast plasma membrane
Authors: Esfahani Mojtaba , Solomon Daniel J. , Mele Lisa , Teter M. Noel 
Published: May 2005

AbstractIn order to gain direct evidence for lipid‐dependent protein conformation in membrane, effects of modification of lipid composition on mobility of spin‐labeled cysteine residues were investigated in the plasma membrane of the yeast Saccharomyces cerevisiae. Conversion of the bulk of phospholipids to diglycerides by treatment of the membrane with phospholipase C substantially enhanced spectral anisotropy. However, alteration of the viscosity of the lipid‐bilayer by enriching the membrane with palmitelaidic or oleic acid had no effect on mobility of spin‐labeled cysteine residues. These observations indicate that while the spin‐labeled residues are not in direct contact with the lipid core of the membrane, there are lipid‐protein interactions to the extent that removal of polar portion of the bulk of phospholipids induces conformational changes in proteins, which in turn restrict mobility of these residues. It is concluded that conformation of membrane proteins depends on lipid structure and that phospholipids have a role in preserving the native conformation of proteins.
The role of temperature in the crystallization of ribosomes in chick embryos
Authors: Barbieri Marcello 
Published: May 2005

AbstractThe relationship between ribosome crystallization and cell degeneration has been studied in chick embryos at various temperatures, and new methods of inducing ribosome microcrystals are described. A model is discussed that reinterprets the role of low temperatures in these phenomena and provides a unitary explanation of the various cases in which the occurrence of ribosome crystallization in chick embryos has been reported.
Phosphoprotein intermediate in the ca2+‐dependent atpase reaction of macrophage plasma membrane
Authors: Schneider C. , Mottola C. , Romeo D. 
Published: May 2005

AbstractATPase activity and phosphorylation by [γ‐32P] ATP of isolated plasma membrane of alveolar macorphages are stimulated in a parallel fashion by physiologic concentrations of Ca2+, with half‐maximal activating effect of this ion at (3–7) × 10−7 M. For various membrane preparations, a direct proportionality exists between Ca2+‐dependent ATPase activity and amount of 32P incorporated. Labeling of membrane attains the steady‐state level by 10 sec at 0°C, and is rapidly reversed by adenosine diphosphate (ADP). K+ decreases the amount of membrane‐bound 32P, mainly by enhancing the rate of dephosphorylation of the 32P‐intermediate. Hydroxylamine causes a release of about 90% of 32P bound to the membrane, thus indicating that the 32P‐intermediate contains an acyl‐phosphate bond. When the labeled plasma membrane is solubilized and electrophoresed on acrylamide gels in the presence of sodium dodecyl sulphate, the radioactivity appears to be largely associated with a single protein fraction of 132,500 ± 2,000 apparent molecular weight. These features of the macrophage Ca2+‐ATPase suggest that the enzyme activity might be part of a surface‐localized Ca2+‐extrusion system, participating in the regulation of Ca2+‐dependent activities of the macrophage.
Structure of the dna binding cleft of the gene 5 protein from bacteriophage fd
Authors: McPherson Alexander , Jurnak Frances , Wang Andrew , Rich Alexander , Molineux Ian 
Published: May 2005

AbstractThe structure of the gene 5 DNA unwinding protein from bacteriophage fd has been solved to 2.3‐Å resolution by X‐ray diffraction techniques. The molecule contains an extensive cleft region that we have identified as the DNA binding site on the basis of the residues that comprise its surface. The interior of the groove has a rather large number of basic amino acid residues that serve to draw the polynucleotide backbone into the cleft. Arrayed along the external edges of the groove are a number of aromatic amino acid side groups that are in position to stack upon the bases of the DNA and fix it in place. The structure and binding mechanism as we visualize it appear to be fully consistent with evidence provided by physical‐chemical studies of the protein in solution.
Nuclear control of tumorigenicity in cells reconstructed by PEG‐induced fusion of cell fragments
Authors: Shay Jerry W. , Clark Mike A. 
Published: May 2005

AbstractThe techniques of somatic cell hybridization have provided a valuable means of studying mechanisms of regulation of mammalian cell differentiation and transformation. Most previous studies have indicated that fusions between tumorigenic and nontumorigenic cells result in hybrid cells that are usually tumorigenic. In recent years it has been demonstrated that the phenotypic expression of tumorigenicity is at least partially due to the extensive chromosome loss that occurs in most interspecific and some intraspecific hybrid cells. In the present study we have utilized enucleation techniques that permit cells to be divided into nuclear (karyoplast) and cytoplasmic (cytoplast) cell fragments. Even though these nuclear and cytoplasmic fragments are metabolically stable for short periods of time, in our hands they ultimately degenerate. Viable cells can be reconstructed by PEG‐induced fusion of karyoplasts to cytoplasts. Since reconstructed cells apparently do not segregate chromosomes, they may provide a clearer understanding of the interactions between the nucleus and the cytoplasm in the control of the expression of tumorigenicity. We have reconstructed cells using karyoplasts from the tumorigenic Y‐1 cell line and cytoplasts from a nontumorigenic cell line, A‐MT‐BU‐A1. In addition we have reconstructed cells containing Y‐1 cytoplasts and A‐MT‐BU‐A1 karyoplasts. The reconstructed cells porduced were assayed for tumorigenicity by their ability to grow in soft agar and in nude mice. The results of these experiments indicate that the reconstructed cells containing a tumorigenic nucleus and a nontumorigenic cytoplasm ultimately are tumorigenic and conversely the reconstructed cells containing a nontumorigenic nucleus and a tumorigenic cytoplasm are nontumorigenic. These experiments support the concept that with these cell lines the nucleus (karyoplast) is sufficient to control the phenotypic expression of tumorigenicity.
The assembly of lipid‐linked oligosaccharides in plant and animal membranes
Authors: Bailey David S. , Dürr Mathias , Burke John , Maclachlan Gordon 
Published: May 2005

AbstractMembrane preparations from growing regions of pea stems and activelydividing mouse L‐cells form lipid‐linked saccharides from GDP‐mannose and UDP‐N‐acetylglucosamine. These lipids have properties which are consistent with those of mono‐and di‐phosphoryl polyisoprenyl derivatives.In experiments using plant membranes, the monophosphoryl derivative labeled with GDP‐(14C) mannose contains mannose only, while the diphosphoryl derivative labeled with the same nucleotide sugar is heterogeneous, containing oligosaccharides corresponding to mannosaccharides of 5, 7, and 9‐12 residues. Only the diphosphoryl polyisoprenyl derivatives are labeled with UDP‐(14C)glucosamine and these contain predominantly chitobiose and N‐acetylglucosamine itself. Unlabeled GDP‐mannose added after UDP‐N‐acetyl (14C)glucosamine results in the formation of higher lipid‐linked oligosaccharides which are apparently the same as those which are labeled with GDP‐(14C)mannose alone. Incubation of the membranes with GDP‐(14C)mannose in the presence of Mn2+, unlabeled UDP‐glucose or unlabeled UDP‐N‐acetylglucosamine results in marked changes in the accumulation of both the polyisoprenyl monophosphoryl mannose and polyisoprenyl diphosphoryl oligosaccharides.Animal cell membranes synthesise lipid‐linked oligosaccharides when incubated with UDP‐N‐acetylglucosamine and GDP‐mannose. These oligosaccharides are similar in size to those synthesised by the plant membranes but their formation is more efficient. The potential roles of these compounds in glycoprotein biosynthesis in both plant and animal tissues is discussed.
Mitotic factors from mammalian cells: A preliminary characterization
Authors: Sunkara Prasad S. , Wright David A. , Rao Potu N. 
Published: May 2005

AbstractThe objective of this study was the preliminary characterization of the factors from mitotic HeLa cells that can induce meiotic maturation in Xenopus laevis oocytes. We found that this factor is a heat‐labile, Ca2+‐sensitive, nondialyzable protein with a sedimentation value of 4‐5S. Furthermore, no new protein synthesis was found to be required for this mitotic factor to induce maturation in the amphibian oocytes. These data suggest that the factors involved in the breakdown of nuclear membrane and the condensation of chromosomes that are associated with three different phenomena, mitosis, meiosis, and premature chromosome condensation, are very similar in different animal species.
Growth of kidney epithelial cells in hormone‐supplemented, serum‐free medium
Authors: Taub Mary , Sato Gordon H. 
Published: May 2005

AbstractMadin Darby canine kidney cells can grow in synthetic medium supplemented with 5 factors – insulin, transferrin, prostaglandin E1, hydrocortisone and triiodothyronine – as a serum substitute. These 5 factors permit growth for one month in the absence of serum, and a growth rate equivalent to that observed in serum‐supplemented medium. Dibutyryl cAMP substitutes for prostaglandin E1 in the medium, suggesting that increased growth of Maden Darby canine kidney cells results from increased intracellular cAMP. Potential applications of the serum‐free medium are discussed. The medium permits the selective growth of primary epithelial cell cultures in the absence of fibroblast over‐growth, and a defined analysis of the mechanisms by which hormones regulate hemicyst formation.
Inhibition of blood coagulation factor XIIIa‐mediated cross‐linking between fibronectin and collagen by polyamines
Authors: Mosher Deane F. , Schad Peter E. , Kleinman Hynda K. 
Published: May 2005

AbstractSoluble fibronectin is found in body fluids and media of cultured adherent cells. Insoluble fibronectin is found in tissue stroma and in extracellular matrices of cultured cells. Fibronectin is a substrate for factor XIIIa (plasma transglutaminase) and can be cross‐linked to collagen and to the α chain of fibrin. We have used sodium dodecyl sulfate‐polyacrylamide gel electrophoresis to investigate the possibility that factor XIIIa ‐mediated cross‐linking is influenced by polyamines. Spermidine inhibited cross‐linking between fibronectin and type I collagen, isolated α1 (I) collagen chains, or iodinated cyanogen bromide fragment 7 of α1 (I) chains (125I‐α1 (I)‐CB7). Half‐maximal inhibition of crosslinking between 125I‐α1 (I)‐CB7 and fibronectin was observed when 0.1 mM spermine or spermidine was present. Spermidine, 0.7 mM, partially inhibited cross‐linking between fibronectin and the α chain of fibrin but failed to inhibit cross‐linking between the fibrin monomers of a fibrin clot. Spermidine also failed to inhibit cross‐linking between fibronectin molecules when aggregation of fibronectin was induced with dithiothreitol. In contrast, 0.7 mM monodansylcadaverine inhibited fibronectin‐collagen, fibronectin‐fibrin, fibronectin‐fibronectin, and fibrin‐fibrin cross‐linking. Spermidine or spermine, 0.7 mM, enhanced the cross‐linking between molecules of partially amidinated fibronectin, suggesting that N1,8‐(di‐γ‐glutamyl)‐polyamine cross‐linkages were formed. Spermidine and spermine failed to enhance cross‐linking between monomers of amidinated fibrin. These results indicate that physiologic concentrations of polyamines specifically disturb transglutaminase‐catalyzed cross‐linking between fibronectin and collagen.
Influence of buffer ions and divalent cations on coated vesicle disassembly and reassembly
Authors: Woodward Michael P. , Roth Thomas F. 
Published: May 2005

AbstractDisruption of the coat of coated vesicles is accompanied by the release of clathrin and other proteins in soluble form. The ability of solubilized coated vesicle proteins to reassemble into empty coats is influenced by Mg2+, Tris ion concentration, pH, and ionic strength. The proteins solubilized by 2 M urea spontaneously reassemble into empty coats following dialysis into isolation buffer (0.1 M MES–1 mM EGTA–1 mM MgCl2–0.02% NaN3, pH 6.8). Such reassembled coats have sedimentation properties similar to untreated coated vesicles. Clathrin is the predominant protein of reassembled coats; most of the other proteins present in native coated vesicles are absent. We have found that Mg2+ is important in the coat assembly reaction. At pH 8 in 0.01 M or 0.1 M Tris, coats dissociate; however, 10 mM MgCl2 prevents dissociation. If the coats are first dissociated at pH 8 and then the MgCl2 raised to 10 mM, reassembly occurs. These results suggest that Mg2+ stabilizes the coat lattice and promotes reassembly. This hypothesis is supported by our observations that increasing Mg2+ (10 μM–10 mM) increases reassembly whereas chelation of Mg2+ by (EGTA) inhibits reassembly. Coats reassembled in low‐Tris (0.01 M, pH 8) supernatants containing 10 mM MgCl2 do not sediment, but upon dialysis into isolation buffer (pH 6.8), these coats become sedimentable. Nonsedimentable coats are noted also either when partially purified clathrin (peak I from Sepharose CL4B columns) is dialyzed into low‐ionic‐strength buffer or when peaks I and II are dialyzed into isolation buffer. Such nonsedimentable coats may represent intermediates in the assembly reaction which have normal morphology but lack some of the physical properties of native coats. We present a model suggesting that tightly intertwined antiparallel clathrin dimers form the edges of the coat lattice.
Glycosaminoglycans of the plasma membranes of renal tubule and liver cells
Authors: Lis Dora , Monis Benito 
Published: May 2005

AbstractGlycosaminoglycans were isolated from plasma membranes of hepatic and renal tubule cells of guinea pig. Plasmalemma of renal tubule cells contained more total glycosaminoglycans, hyaluronic acid, chondroitin‐4 sulfates and chondroitin‐6 sulfates, and less dermatan sulfates and heparin sulfates than liver plasma membranes. These glycocalyx components, owing to their polyanionic properties, may have a role in the transport of water, ions, and macromolecules across the cell membrane.
Structural comparisons of the aggregates of tobacco mosaic virus protein
Authors: Stubbs Gerald , Warren Stephen , Mandelkow Eckhard 
Published: May 2005

AbstractThe coat protein of tobacco mosaic virus forms numerous aggregates, including the small A‐protein, the disk, and two helical forms. The structures of the disk, the helical protein forms, and the virus are compared. Most of the differences are in the conformation of the chain between residues 89 and 113, which lies in the region of protein at the center of the virus, inside the RNA. It is disordered in the disk, but has a fixed conformation in the virus and the protein helices. The differences between the virus and the two helical protein forms are largely in the conformations of arginines and carboxylic acids in this region.
Isolation of cholera toxin receptors from a mouse fibroblast and lymphoid cell line by immune precipitation
Authors: Critchley D. R. , Ansell S. , Perkins R. , Dilks S. , Ingram J. 
Published: May 2005

AbstractCholera toxin receptors have been isolated from both a mouse fibroblast (Balbc/3T3) and mouse lymphoid cell line labeled by the galactose oxidase borotritiide technique. Tritiated receptor‐toxin complexes solubilized in NP40 were isolated by addition of toxin antibody followed by a protein A‐containing strain of Staphylococcus aureus. In both cell types by far the major species of toxin receptor isolated was ganglioside in nature, although galactoproteins were also present in the immune complexes. Whether the galactoproteins form part of a toxin‐receptor complex or are artifacts of the isolation procedure is presently unclear.The relative specificity of cholera toxin for a carbohydrate sequence in a glycolipid suggests that the toxin might prove a useful tool in establishing the function and organization of glycolipids in membranes. For example, interaction of cholera toxin with the mouse lymphoid cell line was shown to result in patching and capping of bound toxin, raising the possibility that the glycolipid receptor interacts indirectly with cytoskeletal elements. Cholera toxin might also be used to select for mutant fibroblasts lacking the toxin receptor and therefore having an altered glycolipid profile. Such mutants might prove useful in establishing the relationship (if any) between modified glycolipid pattern and other aspects of the transformed phenotype. Attempts to isolate mutants, based on the expectation that growth of cells containing the toxin receptor would be inhibited by the increase in cAMP levels normally induced by cholera toxin, proved unsuccessful. Cholera toxin failed to inhibit significantly the growth of either Balbc or Swiss 3T3 mouse fibroblasts although it markedly elevated cAMP levels.
Gliding mycoplasmas are inhibited by cytochalasin B and contain a polymerizable protein fraction
Authors: Maniloff Jack , Chaudhuri Utpal 
Published: May 2005

AbstractStudies are presented on the effect of cytochalasin B (CB) on the growth of five Mycoplasma species, three Acholeplasma species, and one Spiroplasma species. The three gliding mycoplasma species (M) gallisepticum, M pneumoniae and M pulmonis are the only mycoplasmas inhibited by CB. These are the only prolaryotes reported to be inhibited by CB. This suggested that these three mycoplasmas might have some sort of cytoskeletal structure. A protein fraction has been isolated from M gallisepticum which polymerizes in 0.6 M KC1 and depolymerizes when KC1 is removed. This fraction contains a major 58,000‐dalton protein, a 46,000‐dalton protein, and a minor 87,000‐dalton protein.
The regional association of actin and myosin with sites of particle phagocytosis
Authors: Painter Richard G. , McIntosh Ann T. 
Published: May 2005

AbstractContractile proteins are thought to play a causative role in motile processes such as phagocytosis. In order to investigate their role in phagocytosis further, simultaneous immunofluorescence localization of F‐actin and myosin was carried out in resident mouse peritoneal macrophages after phagocytosis of opsonized zymosan particles. Both actin and myosin appeared to concentrate rapidly at sites of particle phagocytosis. The observed concentration of both proteins at such sites preceded ultimate particle engulfment. Cytochalasin B, a drug which was shown to block pseudopod extensions around the particle, did not prevent the concentration of the two contractile proteins at cell‐particle binding sites. This result ruled out path‐length effects as an explanation for the observed concentration of actin and myosin at phagocytic sites. Kinetic analysis showed that actin rapidly concentrates at particle‐cell binding sites within minutes (or less) of contact with cell surface. The two proteins are present throughout the engulfment phase until and after ingestion is complete. Finally, at later times the particles become clustered over the cell nucleus and the particle‐associated actin‐myosin seen earlier is no longer evident.
Hormone‐induced modification of EGF receptor proteolysis in the induction of EGF action
Authors: Fox C. Fred , Wrann Michael , Linsley Peter , Vale Ron 
Published: May 2005

AbstractA proposal that EGF action is mediated through enhanced internalization of EGF receptors is modified to account for more recent evidence. EGF receptors turn over at a rapid rate, and the maintenance of a steady state of EGF receptors on the cell surface is provided through a rapid synthesis of EGF receptors, balancing their removal. This rapid turnover of unoccupied receptors may arise through their removal. This rapid turnover of unoccupied receptors may arise through their internalization and proteolysis in the lysosomes, in much the same way as receptors are internalized and degraded when exposed to EGF, which enhances internalization. This provides a dilemma for the endocytic activation concept, since slight enhancement of receptor internalization gives rise to a strong hormone response. This problem may be solved by the observation that EGF induces a change in its receptor, exposing an otherwise unavailable site for proteolytic cleavage. This hormone‐dependent modification of receptors may be the critical step in the induction of responses to EGF and other hormones that are internalized with their receptors. Both platelet‐derived growth factor (PDGF) and fibroblast growth factor (FGF) are shown to down‐regulate EGF receptors, though transiently, placing still more stringent requirements on the specificity by which hormones might act through endocytic activation of their receptors.
Steroid hormone receptor studies in melanoma model systems
Authors: Markland Francis S. , Horn Diane 
Published: May 2005

AbstractThe Transplantable B‐16 melanotic melanoma carried in syngeneic C57B1/6J female mice and the Syrian hamster melanoma cell line, RPMI 3460, were utilized to determine whether steroid‐hormone receptors are present in animal melanomas. In the B‐16 melanoma, a cytoplasmic‐estrogen receptor is detectable, but there is no evidence for androgen or progestin receptors. Some tumors contain a glucocorticoid‐binding macromolecule. Sucrosedensity gradient centrifugation of cytosol after incubation with [3H]‐estradiol revealed an 8S peak that was suppressed by excess radioinert diethylstilbesterol. Binding varied from 5–35 fmoles per mg cytosol protein. Scatchard analysis of [3H]‐estradiol binding in cytosol yielded a single class of high‐affinity binding sites; the dissociation constant is 6 × 10−10 M. The receptor molecule is shown to be estrogen‐specific by ligand competition assays. In contrast to B‐16 melanoma, no estrogen, androgen, or progestin receptor can be found in the Syrian hamster melanoma cell line. However, a substantial level of specific binding is observed using [3H]‐dexamethasone. Sucrose‐gradient centrifugation of cytosol from this cell line after incubation with [3H]‐dexamethasone revealed a 7S peak that was suppressed by excess radioinert dexamethasone. Scatchard analysis indicated a single class of high affinity sites with a dissociation constant of 2 × 10−9 M. Binding levels from 70–610 fmoles per mg cytosol protein were observed. The Syrian hamster melanoma cells also exhibit a biological response to glucocorticoids: Dexamethasone causes both an inhibition of growth and a decrease in final‐cell density in these cells.