bluuebunny/crossref_metadata_2025_split huggingface dataset:
Carchesium stalk fibrillar matrix as a highly filled polymer network
Authors: Hawkes Richard 
Published: February 2005

AbstractGlycerolated stalks of the sessile peritrich ciliate Carchesium sp. were treated with 10−6 g ion/1 Ca2+ to disrupt the contractile spasmoneme. The resulting preparation consisted primarily of the fibrillar matrix, a dense extracellular meshwork of microfibrils. Some mechanical properties of this preparation have been investigated. The matrix tensile force‐extension ratio relation for an initial stretch was characteristic of a soft, swollen polymer network, elastic modulus in young stalks 1.7 × 105 Nm−2, in mature stalks 4.0 × 105 Nm−2. The higher elastic modulus in mature stalks implies an increase in the interchain cross‐link frequency. In young stalks, elastic modulus was found to be independent of the ambient Ca2+ concentration in the threshold range for spasmonemal contraction. Stalk relaxation was pronouncedly irreversible, showing stress softening and permanent hysteresis on repeated loading. Hysteresis was time independent and stiffness was not recovered after four hours at zero strain. Hysteresis was enhanced by repeated loading to the same tensile force. Stress‐strain hysteresis at a low extension ratio is characteristic of highly filled polymer networks in which polymer chains are interconnected via rigid filler particles as well as directly cross‐linked.
Cytotoxicity of ascorbate and other reducing agents towards cultured fibroblasts as a result of hydrogen peroxide formation
Authors: Peterkofsky Beverly , Prather Willie 
Published: February 2005

AbstractSeveral types of cultured fibroblasts, including chick embryo, human and mouse, were killed by the addition of sodium ascorbate at final concentrations of 0.05–0.25 mM to cultures at the time of inoculation or to attached cells. Ascorbate did not affect the attachment of cells to the substratum. The effect on chick embryo fibroblasts was visible by fours hours and by six hours almost all cells had swelled and were becoming detached. By 24 hours detached cells had either lysed or become crenated in appearance. Other end‐diol reducing agents and also glutathione and cysteine were effective while gulonolactone, a non‐reducing analogue of ascorbate, was ineffective. Preincubation of medium containing ascorbate but no cells, conditions which result in degradation of the vitamin, led to loss of toxicity, indicating that a degradation product was not the lethal agent and that a component of the medium was not converted to a lethal substance. The lethal effect of both ascorbate and glutathione was prevented by the addition of catalase to the medium, suggesting that H2O2 formed by intracellular reactions and then excreted into the medium was the cytotoxic agent. This conclusion was supported by the findings that 0.05 mM H2O2 added to chick embryo fibroblasts was lethal and that the effect of this compound on cellular morphology was almost identical to that of ascorbate.
The in vivo effect of dimethyl sulphoxide (DMSO) on protein synthesis and the polyribosome profile in paramecium
Authors: Reisner A. H. , Bucholtz Carolyn 
Published: February 2005

AbstractWhen Paramecium tetraurelia in log phase growth is treated with 4% dimethyl sulphoxide (DMSO) for five minutes the amount of polyribosomes is reduced 3‐ to 4‐fold while there is a corresponding increase in 80s ribosomal material. Reducing the concentration of DMSO to 1% allows immediate reversal of the condition.Paramecium polyribosomes subjected to 4% DMSO either in whole cell homogenates or during purification through sucrose density gradients appear unaffected while cycloheximide at concentrations up to 100 μg/ml did not prevent DMSO from exerting its effect in vivo.Analyses of 14C amino acid incorporation experiments indicated a strict correspondence between the effect of DMSO on polyribosomes and overall protein synthesis. The reduction of acid precipitable radioactivity in the polyribosomal region after DMSO treatment was associated with a corresponding increase in radioactivity in the 80s region. There was no comparable increase in the acid precipitable radioactivity in the soluble fraction.The overall results of the study suggest that DMSO acts on polyribosomes indirectly through some unknown primary reaction with cell constituents, and that the mode of action is such as to cause the release of ribosomes from messenger RNA (mRNA) rather than to prevent initiation of the ribosome‐mRNA complex. Our data suggest that the effect may be selective.Finally, it is of interest that high concentrations of DMSO (above 8%) appear to have the opposite effect of lower concentrations of DMSO, i.e., they appear to “freeze” the ribosomes to mRNA.
Enzyme inactivation by a cellular neutral protease: Enzyme specificity, effects of ligands on inactivation, and implications for the regulation of enzyme degradation
Authors: Levy Michael R. , McConkey Charles L. 
Published: February 2005

AbstractA protease from Tetrahymena pyriformis inactivated eight of nine commercially available enzymes tested, including lactate dehydrogenase, isocitrate dehydrogenase (TPN‐specific), glucose‐6 phosphate dehydrogenase, D‐amino acid oxidase, fumarase, pyruvate kinase, hexokinase, and citrate synthase. Urate oxidase was not inactivated. Inactivation occurred at neutral pH, was prevented by inhibitors of the protease, and followed first order kinetics. In those cases tested, inactivation was enhanced by mercaptoethanol. Most of the enzyme‐inactivating activity was due to a protease of molecular weight 25,000 that eluted from DEAE‐Sephadex at 0.3 M KCl. A second protease of this molecular weight, which was not retained by the gel, inactivated only isocitrate dehydrogenase and D‐amino acid oxidase. These two proteases could also be distinguished by temperature and inhibitor sensitivity. Two other protease peaks obtained by DEAE‐Sephadex chromatography had little or no enzyme inactivating activity, while another attacked only D‐amino acid oxidase.At least six of the enzymes could be protected from proteolytic inactivation by various ligands. Isocitrate dehydrogenase was protected by isocitrate, TPN, or TPNH, glucose‐6‐dehydrogenase by glucose‐6‐P or TPN, pyruvate kinase by phosphoenolypyruvate or ADP, hexokinase by glucose, and fumarase by a mixture of fumarate and malate. Lactate dehydrogenase was not protected by either of its substrates or coenzymes. Citrate synthase was probably protected by oxalacetate.Our data suggest that the protease or proteases discussed here may participate in the inactivation or degradation of at least some enzymes in Tetrahymena. Since the inactivation occurs at neutral pH, this process could be regulated by variations in the cellular levels of substrates, coenzymes, or allosteric regulators resulting from changes in growth conditions or growth state. Such a mechanism would permit the selective retention of enzymes of metabolically active pathways.
Quantitation of mitochondrial DNA, RNA, and protein in starved and starved‐refed rat liver
Authors: Stocco D. M. , Cascarano J. , Wilson M. A. 
Published: February 2005

AbstractThe purpose of this study was to investigate the problem of mitochondrial biogenesis in rat liver. The approach consisted of isolating mitochondria from control, 6 day starved and 6 day starved‐5 day refed rats and comparing their DNA, RNA and protein content. This was performed by isolating the mitochondria by reorienting rate zonal centrifugation in sucrose gradients. It was found that six days of starvation resulted in a loss of 30% of the body weight, 55% of the liver weight, 40% of the mitochondrial protein, 60% of the mitochondrial RNA, but only 20% of the mitrochondrial DNA. It was also shown that refeeding of the rats for five days resulted in a restoration to normal or near normal levels in all the parameters measured. Further experiments employing the incorporation of 3H‐TTP into isolated mitochondria indicated that the maintenance of mitochondrial DNA was not the result of continuous DNA synthesis.
Accumulation of polyploid cells and G2‐phase cells during ascites tumor growth
Authors: Andersson Gunnar 
Published: February 2005

AbstractEhrlich ascites tumor cells from the plateau phase of growth were transplanted into new hosts, pulse‐labeled with tritiated thymidine and blocked with repeated injections of vinblastine. When unlabeled cells were analyzed for their cellular DNA content utilizing a cytophotometric technique it was found that in relation to the total number of cells (labeled plus unlabeled), 13% had a 2C DNA content, 36% a 4C DNA content and 5% an 8C DNA content at 0.5 hours after transplantation. By 24 hours the distributions changed dramatically: the initially unlabeled 2C cells were now 4C, the 36% of the cells that were initially 4C partitioned into 24% that were still 4C and 12% that progressed to 8C, and the initial 8C cells remained 8C. These studies indicate that the accumulation of 4C cells during the plateau phase of growth is due to a combination of G2 diploid and G1 tetraploid cells.
Peritoneal exudate cells. IV. Characterization of colony forming cells
Authors: Lin Hsiu‐San , Freeman Pamela G. 
Published: February 2005

AbstractThe adherence, phagocytic activity and buoyant density of mouse peritoneal exudate colony forming units (CFU‐PE) were investigated. There was a significant enrichment in the proportion of CFU‐PE in the adherent cells population, defined as cells adhering to a plastic surface within 30 minutes of incubation. The phagocytic activity of CFU‐PE was studied by incubating exudate cells with iron particles for 45 minutes. The cells were then separated into phagocytic and non‐phagocytic cell fractions by passing the incubation mixture through a magnetic field. A significant enrichment of CFU‐PE was seen in the phagocytic cell fraction. When exudate cells were fractionated in a Ficoll discontinuous density gradient, more than 88% of CFU‐PE were recovered at the 16/18% and 18/20% interfaces. It is concluded that CFU‐PE are adherent cells, have strong phagocytic activity and have a buoyant density between 1.0562 and 1.0703. When bone marrow cells were studied by these techniques, the committed stem cells for both granulocytes and macrophages (CFU‐C) were enriched in both non‐adherent cell and non‐phagocytic cells populations. In the Ficoll density gradient, CFU‐C banded at a heavier density region than CFU‐PE.
The effect of colony stimulating factor on the synthesis of ribonucleic acid by mouse bone marrow cells in vitro
Authors: Burgess Antony W. , Metcalf Donald 
Published: February 2005

AbstractThe effect of granulocyte‐macrophage colony stimulating factor (GM‐CSF) on the synthesis of RNA in liquid cultures of mouse bone marrow, spleen, thymus, peritoneal, peripheral blood leukocytes and lymph node cells was investigated. GM‐CSF appeared to stimulate RNA‐synthesis in syngeneic bone marrow cells within ten minutes of adding it to the culture. In the presence of GM‐CSF bone marrow cultures maintained their initial rate of RNA synthesis for approximately ten hours. GM‐CSF had no apparent effect on the uptake of3H‐uridine into bone marrow cells. This stimulation was still observed in the presence of puromycin and cycloheximide, but was abrogated by actinomycin D. The magnitude of the stimulation was not affected by the density of cells between 1 and 20 × 106cells/ml but was slightly smaller at 0.1 and 40 × 106cells/ml. Increasing concentration of GM‐CSF (up to 2 × 105units per ml) led to increased stimulation of RNA synthesis in bone marrow cells, but a significant stimulation could be detected at concentrations as low as 800 units/ml.GM‐CSF did not significantly stimulate RNA synthesis in spleen, thymus, mesenteric or subcutaneous lymph node cells. However a small stimulation was observed in peripheral blood leukocytes and peritoneal cells.Autoradiographic studies showed that GM‐CSF stimulated RNA synthesis in blast cells, myelocytes, metamyelocytes and polymorphs. Nucleated erythroid cells showed no increased labeling with GM‐CSF. Labeling in lymphoid‐like cells was highly variable but the level of labeling did not appear to be influenced by GM‐CSF.
Studies on a fractionated murine fibrosarcoma: A reproducible method for the cautious and a caution for the unwary.
Authors: Sheridan J. W. , Finlay‐Jones J. J. 
Published: February 2005

AbstractA technique is described for the dissociation and fractionation by isopycnic centrifugation (4,000 × g, 60 minutes, 4°C) in linear bovine albumin density gradients (12 ml, pH 5.2 real osmolality 333 mmol/Kg water, 1.030–1.075 g/cm3) of cells (⩽ 3 × 107/gradient) released by a strictly standardised combination of mechanical and enzymatic means from a transplantable methylcholanthrene induced BALB/c fibrosarcoma. Optimal conditions for reproducible localisation of cell bands with maintenance of both satisfactory resolution and satisfactory viable cell recovery (> 80%) were established by means of a series of simultaneous double fractionation experiments. When rebanding was performed under these conditions the density of the median of the cell count of the refractioned cells shifted less than 0.0005 g/cm3. Experiments also showed that close adherence to certain aspects of the tissue dissociation and fractionation protocol was necessary to avoid reduced cell yields and viabilities, density‐dependent selective cell losses, reductions in resolution and shifts in the location of cell bands. Other aspects of the protocol were tolerant to variation without introducing artefacts.
The effects of neuraminidase on concanavalin a agglutination of erythrocytes: Evidence for adsorption of neuraminidase to erythrocyte membrane
Authors: Lamont J. Thomas , Isselbacher Kurt J. 
Published: February 2005

AbstractNeuraminidase‐treated human erythrocytes, but not untreated erythrocytes, were agglutinated by concanavalin A. The degree of concanavalin A agglutinability was not directly related to sialic acid removal by neuraminidase. While maximal sialic acid release was obtained with 5 units neuraminidase/2 × 109 erythrocytes, maximal concanavalin A agglutination was only obtained after exposure to 20 units neuraminidase. Binding of 3H‐concanavalin A by erythrocytes was 10‐fold higher with rabbit compared to human red cells.Neuraminidase treatment of human erythrocytes caused a relative increase in 3H‐concanavalin binding, but the absolute amount was still 10‐fold less than that bound to rabbit erythrocytes. Specific adherence of neuraminidase to Con A‐Agarose could not be demonstrated. There was no evidence for contamination of the neuraminidase preparation with proteases using a sensitive assay. These studies suggest that neuraminidase adsorbs to erythrocyte membranes and leads to concanavalin A agglutination of human erythrocytes by a mechanism other than removal of sialic acid.
Interrelationships between water and cellular metabolism in Artemia cysts. VI. RNA and protein synthesis
Authors: Clegg James S. 
Published: February 2005

AbstractUsing 14CO2 as a labelled precursor the relationship between the initiation of protein and RNA synthesis, and water concentration, has been examined in cysts (encysted embryos) of the brine shrimp, Artemia salina. Although incorporation of radioactivity into amino acids and nucleotides occurred in cysts at hydrations as low as 0.3 g H2O/g dried cysts, incorporation into proteins and RNA was not measurable until the cysts had achieved a hydration in the range of 0.6–0.6 g/g. In no case was radioactivity detected in DNA of unemerged cysts. Fully hydrated cysts (about 1.3 g/g) that were actively synthesizing proteins and RNA, stopped doing so when dehydrated to levels below the same hydration range: thus, the hydration dependence does not involve appreciable hysteresis. The hydration range required to initiate synthesis of these macromolecules is essentially the same as that previously shown to initiate embryonic development.
The binding sites of cytochalasin D. I. Evidence that they may be peripheral membrane proteins
Authors: Tannenbaum Janet , Tanenbaum Stuart W. , Godman Gabriel C. 
Published: February 2005

AbstractBinding sites for tritiated cytochalasin D (3H‐CD) on the isolated plasma membrane from HEp‐2 cells were reversibly inactivated, but not dissociated from the membrane, by dialysis in 0.6 M KCl. Activity was restored by subsequent dialysis in 0.06 M KCl. Treatment with 0.2 mM ATP at low ionic strength also inactivated these sites, apparently irreversibly. Extraction of the membrane with 6% Triton X‐100 removed 75% of its protein, resulting in a two‐fold increase in specific binding activity for 3H‐CD. Both high and low affinity binding sites were retained by the detergent‐extracted membrane; at least 60% of the high affinity sites were resistant to this treatment. Evidence is presented for the attachment to the HEp‐2 plasma membrane of both actin and myosin. The results support the tentative conclusion that plasma membrane binding sites for 3H‐CD are peripheral proteins on the cytoplasmic face of the membrane. They are consistent with the hypothesis that myosin may be the location of the high affinity binding site and actomyosin may be the low affinity site. Comparison of these observations with those reported for the congeneric drug, cytochalasin B, suggests that CD binding sites differ from the high affinity site for cytochalasin B.
The relation of cycling of intracellular pH to mitosis in the acellular slime mould Physarum polycephalum
Authors: Gerson Donald F. , Burton Alan C. 
Published: February 2005

AbstractThe relation between intracellular pH and the mitotic cycle of Physarum polycephalum was studied by two independent techniques. Both techniques revealed a long term cycling of intracellular pH which has the same period as the mitotic cycle. Qualitative detection of the changes in intracellular pH was made by measuring the changes in fluorescence of 4‐methylesculetin which had been absorbed by the plasmodium. Quantitative measurements of intracellular pH were made throughout the mitotic cycle with antimony micro pH electrodes. The cycle of intracellular pH is sinusoidal in appearance. The maximum intracellular pH (pH 6.6) occurred at, or very near to, mitosis, and was approximately 0.6 pH units higher than the minimum pH, which occurred near the middle of the mitotic cycle.
Conditions controlling the proliferation of haemopoietic stem cells in vitro
Authors: Dexter T. M. , Allen T. D. , Lajtha L. G. 
Published: February 2005

AbstractA liquid culture system is described whereby proliferation of haemopoietic stem cells (CFU‐S), production of granulocyte precursor cells (CFU‐C), and extensive granulopoiesis can be maintained in vitro for several months. Such cultures consist of adherent and non‐adherent populations of cells. The adherent population contains phagocytic mononuclear cells, “epithelial” cells, and “giant fat” cells. The latter appear to be particularly important for stem cell maintenance and furthermore there is a strong tendency for maturing granulocytes to selectively cluster in and around areas of “giant fat” cell aggregations. By “feeding” the cultures at weekly intervals, between 10 to 15 “population doublings” of functionally normal CFU‐S regularly occurs. Increased “population doublings” may be obtained by feeding twice weekly. The cultures show initially extensive granulopoiesis followed, in a majority of cases, by an accumulation of blast cells. Eventually both blast cells and granulocytes decline and the cultures contain predominantly phagocytic mononuclear cells.Culturing at 33°C leads to the development of a more profuse growth of adherent cells and these cultures show better maintenance of stem cells and increased cell density.When tested for colony stimulating activity (CSA) the cultures were uniformly negative. Addition of exogenous CSA caused a rapid decline in stem cells, reduced granulopoiesis and an accumulation of phagocytic mononuclear cells.
Cells regulate theri proliferation through alterations in transition probability
Authors: Shields Robert , Smith James A. 
Published: February 2005

AbstractThe proliferation of 3T3, 3T6 and SV3T3 cells was examined by time lapse cinephotography under a number of different growth conditions. It was found that the frequency distributions of intermitotic times of cells with widely different proliferation rates are qualitatively and quantitatively explained by the transition probability model of the cell cycle (Smith and Martin, 1973). The behaviour of quiescent cells was characterized by very low values of the transition probability. No “out of cycle” or G0 compartment of cells was detectable. From a consideration of these results and those in the literature it appears that the rate of cell proliferation is determined by the value of the “transition probability” (P), and that it is the biochemical manifestation of this parameter that regulates cell growth in vitro and in vivo.
Influence of flow velocity and cell concentration on dynamic adhesion of erythrocytes to glass surface
Authors: Kowalczynska Hanna M. 
Published: February 2005

AbstractComparative studies were carried out on dynamic adhesion of 51Cr‐labelled erythrocytes to the surface of glass beads in the presence of serum in the medium (50 μg of protein/ml) and in protein‐free medium. The influence of cell concentration (within the range 4 x 105 to 8 x 106/ml) and of cellular flow velocity (within the range 1.5–0.4 cm/min) on the value of adhesion was investigated.It was found that when serum was present in the medium, the decisive influence on erythrocyte adhesion was exerted by the velocity with which the cells pass through the glass beads layer. Cell concentration under these conditions has only a very slight effect. When the medium does not contain serum, erythrocyte adhesion to the bead layer seems to depend on both cell concentration and flow velocity.Preliminary data were obtained concerning the release of 51Cr from the bead layer after erythrocyte adhesion.