bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reversion in expression of hypoxanthine‐guanine phosphoribosyltransferase in 6‐thioguanine resistant neuroblastoma: Evidence for reduced enzyme levels associated with unaltered catalytic activity
Authors: Skaper Stephen D. , Spector Elaine B. , Seegmiller J. Edwin 
Published: February 2005

AbstractFive clones of mouse neuroblastoma cells able to grow in hypoxanthine‐aminopterin‐thymidine containing medium were isolated from a hypoxanthine‐guanine phosphoribosyltransferase (HGPRT; EC 2.4.2.8; IMP: pyrophosphate phosphoribosyltransferase) deficient cell line. These hypoxanthine‐aminopterin‐thymidine resistant revertant clones had 45–55% of wild‐type cell HGPRT activity. Kinetic studies indicated that the HGPRT in revertant clones had a reduced maximal velocity as compared to wild type cells based on cell protein. Apparent Km values of HGPRT for hypoxanthine and 5‐phosphoribosyl‐1‐pyrophosphate were similar in wild‐type and revertant cells. Heat inactivation studies demonstrated a similar heat lability for HGPRT in revertant and wild‐type cells. An antibody fraction prepared from serum of rabbits immunized with HGPRT partially purified from mouse liver was used to measure the amount of cross‐reacting material in normal and revertant clones. The revertant clones had one‐half the amount of cross‐reacting material present in wild‐type cells, based on a given amount of cell protein. These data indicate that the revertant cells may contain fewer HGPRT molecules with unaltered catalytic activity.
Accelerated calcium ion uptake in murine thymocytes induced by concanavalin A
Authors: Ozato Keiko , Huang Leaf , Ebert James D. 
Published: February 2005

AbstractThe mechanism of enhancement of Ca2+ uptake by the T cell mitogen concanavalin A (Con A) was studied in murine thymocytes. Native Con A enhanced the rate of Ca2+ uptake as much as 9‐fold, an increase being observed within five minutes after Con A addition. The effect of Con A was reversed completely by α‐methyl mannopyranoside (α‐MM). Increased Ca2+ uptake was observed with increasing concentrations of Con A, between 2 and 400 μg/ml, indicating that the stimulation of Ca2+ uptake is not restricted to mitogenic lectin concentrations (0.5‐2 μg/ml). Succinyl Con A exhibits only a slight effect in the same concentration ranges as native Con A. Ca2+ uptake, both in the absence and presence of Con A, is strongly dependent on energy metabolism and is carrier mediated. The augmentation of Ca2+ uptake by native Con A is due to an enhanced Vmax. Uptake of the anion, CrO42–, by thymocytes, found to be a nonsaturable process, was also enhanced by Con A. The effect of Con A on CrO42− permeability appears to be independent of its effect on Ca2+ uptake.
Free ribosomes and growth stimulation in human peripheral lymphocytes: Activation of free ribosomes as an essential event in growth induction
Authors: Cooper Herbert L. , Braverman Richard 
Published: February 2005

AbstractDuring the initial ten hours of growth in lymphocytes stimulated by phytohemagglutinin, the cells are converted from a state in which over 70% of all ribosomes are inactive free ribosomes, to one in which over 80% of ribosomes are in polysomes or in native ribosomal subunits. In this initial period, there was a neglible increase in total ribosomal RNA due to increased RNA synthesis, and abolition of ribosomal RNA synthesis with low concentrations of actinomycin D did not interfere with polysome formation. Therefore, the conversion is accomplished by the activation of existing free ribosomes rather than by accumulation of newly synthesized particles. The large free ribosome pool of resting lymphocytes is thus an essential source of components for accelerated protein synthesis early in lymphocyte activation, before increased synthesis can provide a sufficient number of new ribosomes. Free ribosomes accumulate once more after 24 to 48 hours of growth, when RNA and DNA synthetic activity are maximal. This reaccumulation of inactive ribosomes at the peak of growth activity may represent preparation for a return to the resting state where cells are again susceptible to stimulation.Activation of free ribosomes to form polysomes appears to involve modification of at least two steps: (a) dissociation of free ribosomes with stabilization as native subunits, and (b) adjustment of a rate‐limiting step at initiation.
The regulation by fibroblast growth factor of early transport changes in quiescent 3T3 cells
Authors: Quinlan Dennis C. , Hochstadt Joy 
Published: February 2005

AbstractThis study involves the use of fibroblast growth factor (FGF) as a substitute for exogenous serum to examine the early transport changes which occur when quiescent 3T3 cells re‐initiate active growth. FGF, in nanogram amounts, together with insulin and dexamethasone, can induce mitogenesis and mitosis in 3T3 cells GO‐arrested by holding in growth medium containing 0.8% calf serum. In terms of quiescent cell transport activity enhancement, FGF is 300,000‐fold more effective than fresh serum, on a protein basis. In addition, very short exposure of serum‐depleted cells to FGF indicates that a distinct temporal or time sequence exists in the transport system activation process. For example, uptake of α‐aminoisobutyric acid (AIB) and uridine are stimulated very rapidly, whereas hypoxanthine uptake does not respond until much later. Closer analysis shows that AIB uptake is maximally enhanced within zero to two minutes after FGF addition to cells. Finally, the stimulatory effect of FGF on transport system activities is specific in terms of the proliferative state of the cells to which it is added, and in terms of the uptake systems which respond to it.
Osmotic properties of human lymphocyte
Authors: Hempling H. G. , Thompson S. , Dupre A. 
Published: February 2005

AbstractThe osmotic properties of human lymphocytes isolated from 15 ml of venous blood were examined. Measurements of the permeability of the membrane to water under an osmotic gradient were also made. The Boyle‐Van't Hoff relation held very well for the human lymphocyte when the cells were shrunken in hyperosmotic media to concentrations twice isosmotic. The volume of osmotically inactive material or “b” value averaged 32% of the mean corpuscular volume. These values were independent of temperature. Ponder's R ranged between 0.8 and 0.9. The average value for Lp, the hydraulic coefficient was 0.46 μ/min atm ± 0.02 (S.E.M.) at 25°C. No significant effect of age, sex, or race was noted. The effect of temperature between 10°C and 37°C was measured and heats of activation between 11.1 and 17.4 kcal/mole were calculated with a mean of 14.1 kcal/mole ± 1.6 (S.E.M.) Concanavalin A at 10 μg/ 1.5 ± 106 lymphocytes produced blastogenesis of 25% or more of the lymphocytes without clumping, agglutination, or toxicity. The mean corpuscular volume increased by 21% after 72 hours due to an increase in the “b” value which increased by 80%. The volume of free water remained constant. Histograms of the distribution of cell volumes showed that volume changes were uniform throughout the population with no evidence of agglutination or clumping. The significance of these results is discussed in the context of membrane fluidity and the state of intracellular water.
Cytotoxicity of commonly used solvents at elevated temperatures
Authors: Li Gloria C. , Hahn George M. , Shiu Esther C. 
Published: February 2005

AbstractAt 43°C (but not at 41°C), organic solvents used to dissolve water‐insoluble chemotherapeutic agents become themselves lethal to cells. This finding is not unique to Chinese hamster cells (HA‐1); mouse mammary sarcoma cells (EMT‐6) behave similarly. The solvent concentrations involved are in the range of those needed to make drug solutions. Hence experiments measuring drug‐cell interactions at elevated temperatures must include controls which independently measure solvent effects.
Growth stimulating activity in bovine pituitary extract specific for a rat mammary carcinoma cell line
Authors: Kano‐Sueoka Tamiko , Campbell Gerald R. , Gerber Michael 
Published: February 2005

AbstractWe report the isolation of a bovine pituitary growth factor (MGF) for a rat mammary carcinoma cell line, 64‐24, which was isolated from a highly hormone‐dependent mammary tumor. The MGF has been partially purified by a series of Diaflo ultrafiltration membrane sievings, isoelectric focusing and Sephadex columns. The MGF has a molecular weight of ∼︁ 1,000 to 2,000 daltons and has a U.V. absorption spectrum typical for a polypeptide. Its isoelectric point is ∼︁ pH 3.8–4.0. The factor is heat stable. The growth stimulating activity of the MGF does not stimulate other rat cell lines (22‐1, RMG or HTC lines) but is specific for the 64‐24 mammary tumor cell line. The MGF is not among previously reported pituitary hormones or growth factors.
Proliferation and differentation of normal granulopoietic cells in continuous bone marrow cultures
Authors: Williams Neil , Jackson Heather , Rabellino Enrique M. 
Published: February 2005

AbstractModified conditions are reported for successful continuous bone marrow cultures with stem cell self‐renewal and granulocyte‐macrophage differentiation. Cells cultured over several weeks were found to be identical to freshly isolated bone marrow cells. Polymorphic neutrophils derived from cultures and primary bone marrow neutrophils both showed C3 and IgG receptors and both actively phagocytosed foreign particles. Cultured and normal CFU‐c were identical, both in their dose responsiveness to CFS and in their sedimentation rate characteristics.
Studies on phosphoglucose isomerase from cultured human fibroblasts: Absence of detectable ageing effects on the enzyme
Authors: Shakespeare Valerie , Buchanan J. H. 
Published: February 2005

AbstractSome properties of the enzyme phosphoglucose isomerase (PGI) from the foetal lung fibroblast strain MRC‐5 have been investigated throughout the in vitro lifespan of this cell strain.No significant age‐related alterations in specific activity or thermostability of PGI could be detected. Titration of enzymatic activity with antibody directed against purified PGI showed no detectable differences in PGI from extracts of early passage cells compared with enzyme from senescent cells.The effect of p‐fluorophenylalanine incorporation on PGI was examined in early passage fibroblasts. Thermostability studies showed increased heat lability of PGI from analogue treated cells when compared with enzyme from control cells at the same passage. However, no inactive PGI protein could be detected by antiserum titration in extracts from analogue‐treated cells.The results indicate that no significant amount of altered or inactive PGI is produced in ageing fibroblasts.
Protein turnover in senescent cultured chick embryo fibroblasts
Authors: Kaftory A. , Hershko A. , Fry M. 
Published: February 2005

AbstractThe over‐all rates of protein synthesis, degradation and net accumulation were estimated in rapidly growing young and slowly doubling old cultures of chick fibroblasts. We find that not only the rate of protein synthesis is reduced in senescent cultures, but the average rate of protein degradation is also slowed down considerably. This decrease in the rate of protein breakdown in aging cells stands in contrast with the previously observed acceleration of this process by other conditions (such as serum deprivation or overcrowding) that lead to the cessation of cellular growth. Though the retarded protein degradation may contribute to the accumulation of abnormal proteins in senescen cells, we find that the breakdown of grossly abnormal puromycin peptides proceeds equally rapidly in young and old cultures.The protein content of senescent cells increase by 1.8‐fold as compared to young cells, while the average cell volume is increased even more (almost 5‐fold). By contrast, consideration of the over‐all balance of protein metabolism in these cells indicaes that the average concentration of metabolically turning‐over proteins is somewhat higher in senescent than in young fibroblasts.
Age‐related and carcinogen‐induced alterations of the extracellular growth factor requirements for cell proliferation in vitro
Authors: Swierenga S. H. H. , Whitfield J. F. , Boynton A. L. 
Published: February 2005

AbstractCells from thigh muscles of fetal rats proliferate readily in vitro in medium containing homologous adult rat “plasma.” As the donor animals mature, these cells become unable to make DNA and proliferate in “plasma” medium, but retain an ability to proliferate in medium containinig fetal bovine serum (FBS). This age‐related loss of the ability to proliferate in “plasma”‐medium is due to an increasing need by the cells for an exogenous prereplicative promoter which is found in FBS and a crude preparation of bovine luteinizing hormone. Adult cells (and possibly fetal cells) also require a “cycle‐completion” factor which is found in FBS and adult rat “plasma.” The requirements for such external proliferative promoters is completely eliminated by neoplastic transformation in vivo, and neoplastic adult cells isolated from a nickel sulfide‐induced mixed rhabdomyo‐fibro‐sarcoma can make DNA and proliferate in vitro in the complete absence of exogenous growth factors.
Assay of ribonucleotide reduction in nucleotide‐permeable hamster cells
Authors: Lewis William H. , Kuzik Brian A. , Wright Jim A. 
Published: February 2005

AbstractRibonucleotide reduction was measured in Chinese hamster ovary cells made permeable to nucleotides by treatment with the detergent Tween‐80. When compared to the respective ribonucleotide reductase activity in partially purified cell extracts, CDP and GDP reductase activities in permeabilized cells responded in a similar fashion to dithiothreitol, pH, MgCl2, FeCl3, substrate concentration and the presence of positive or negative allosteric effectors. At low protein concentrations both CDP and GDP reduction with whole cells increased linearly with cell number and was greater than the activity in corresponding cell extracts.Permeabilized cells were used to measure the level of CDP and GDP reductase in a hamster cell line resistant to the cytotoxic effects of hydroxyurea. The hydroxyurea‐resistant cell line contained four to ten times more CDP and GDP reductase activity compared to parental or revertant cell lines.The permeabilized cell assay was also used to measure CDP and GDP reductase activities in Chinese hamster ovary cells synchronized by isoleucine starvation. CDP reductase activity was low in G1 arrested cells but increased 10‐fold by 16 hours after the readdition of isoleucine to the growth medium. GDP reductase, which is present at much higher levels, is similarly induced after isoleucine addition, but only by 2‐fold. The maximum activity of both CDP and GDP reductase occurred from 14 to 16 hours after isoleucine addition, which corresponded to the period of maximum DNA synthesis.
Phenylalanine hydroxylase in melanoma cells
Authors: Breakefield Xandra O. , Castiglione Carmela M. , Halaban Ruth , Pawelek John , Shiman Ross 
Published: February 2005

AbstractA pigmented subclone of Cloudman S91 melanoma cells, PS1‐wild type, can grow in medium lacking tyrosine. This ability is conferred by phenylalanine hydroxylase activity, and not by tryptophan hydroxylase, tyrosine hydroxylase or tyrosinase activities, although the latter activity is also present in these cells. Conversion of phenylalanine to tyrosine was measured in living cells by chromatographic identification of the metabolites of [14C]phenylalanine and in cell extracts using a sensitive assay for phenylalanine hydroxylase. Phenylalanine hydroxylase activity in melanoma cell extracts was identified by its inhibition with p‐chlorophenylalanine and not with 6‐fluorotryptophan, 3‐iodotyrosine, phenylthiourea, tyrosine or tryptophan; and by adsorption with antiserum prepared against purified rat liver phenylalanine hydroxylase, and migration of immunoprecipitable activity with authentic phenylalanine hydroxylase subunits in sodium dodecyl sulfate‐polyacrylamide gel electrophoresis.
Adaptation to cycloheximide of macromolecular synthesis in Tetrahymena
Authors: Wang Ting‐Chung , Hooper Alan B. 
Published: February 2005

AbstractCycloheximide (CHI) at 10 ng/ml partially inhibited protein synthesis in exponential cultures of Tetrahymena Sp. At 20 ng/ml or greater, inhibition was complete. When protein synthesis was inhibited to any extent, cell division ceased immediately. In all instances where measured, synthesis of RNA and DNA also ceased. After a period of delay, cellular functions reinitiated in the order: (i) protein synthesis, (ii) DNA synthesis and, (iii) RNA synthesis and cell division. The delay in cell division was divided into three phases of: I, zero; II, low; and, III, fully recovered rates of exponential protein synthesis. The length of the three phases increased with increasing concentration of CHIPrior growth of cells for one generation in the presence of 7.5 ng/ml CHI (facilitation) eliminated phase I and slightly decreased phases II and III following subsequent challenge with an inhibitory concentration of CHI. Facilitation for six generations further decreased phases II and III. Protein synthesis and cell division were not inhibited during facilitationIn the culture, succinate dehydrogenase activity did not increase during the delay but increased normally at the onset of division. In contrast, NADPH‐cytochrome c reductase activity continued to increase for an hour after inhibition of protein synthesis, was constant for a period and did not increase again until an hour after reinitiatoin of cell division and RNA synthesisInhibition of division of all cells was immediate and reinitiation of synthesis and cell division was non‐synchronous.
Reciprocal regulation of glucose and glutamine utilization by cultured human diploid fibroblasts
Authors: Ronald Zielke H. , Ozand Pinar T. , Tyson Tildon J. , Sevdalian David A. , Cornblath Marvin 
Published: February 2005

AbstractHuman diploid fibroblasts utilize both glucose and glutamine as energy sources. The utilization of glutamine by fibroblasts is regulated by glucose, and vice versa. This conclusion is supported by the following observations: (1) essentially identical growth rates were observed in Eagle's minimum essential medium (MEM)3 in which the glucose concentration was either 5.5 mM or was maintained between 25 and 40 μM, (2) the total glutamine utilization by fibroblasts increased at least 30% in medium with 25 μM to 70 μM glucose compared to medium with 5.5 mM glucose, while the rate of glutamine‐1 or 5‐14C oxidation to CO2 increased 5‐fold as the glucose concentration was decreased to zero, (3) 2 mM glutamine inhibited glucose‐6‐14C oxidation by 88% and stimulated glucose‐1‐14C by 77% in log phase cells and (4) glutamine oxidation in normal medium contributed approximately 30% of the energy requirement of human diploid fibroblasts.
Role of fatty acids in growth‐promoting effect of serum albumin on hamster cells in vitro
Authors: Nilausen Karin 
Published: February 2005

AbstractDialyzed serum albumin had considerable growth‐promoting effect on cultivated hamster cells. This effect was virtually lost on removal of the fatty acids, and it was completely restored by recombination of the fatty acid‐free albumin with the isolated and purified fatty acids.The role of albumin itself appeared to be largely that of a carrier of fatty acids, protecting the cells against toxic effects of fatty acids in free solution. This conclusion was based on two observations: Fatty acids in the absence of albumin were growth‐inhibitory except in extremely dilute solutions, and betalactoglobulin, a protein possessing, like albumin, the ability to bind and release fatty acids, could replace albumin in the presence of fatty acids with similar growth‐promoting effect.Examination of individual molecular types of fatty acids showed that all unsaturated acids tested were growth‐promoting, whereas the saturated acids were growth‐inhibiting, with the exception of stearic acid in low concentrations.Although the possibility of a mitotic triggering effect was not excluded, the fatty acids presumably stimulated growth by providing substrate for cellular metabolism, since there was a direct relationship between the degree of growth stimulation and the duration of exposure of cells to the fatty acids.
Production by spleen and lymph node cells of conditioned medium with erythroid and other hemopoietic colony‐stimulating activity
Authors: Metcalf D. , Johnson G. R. 
Published: February 2005

AbstractPokeweed mitogen‐stimulated suspension cultures of mouse spleen cells produced conditioned medium able to stimulate granulocyte‐macrophage, eosinophil and megakaryocyte colony formation in agar cultures of C57BL marrow cells and granulocyte‐macrophage and erythroid colony formation in agar cultures of CBA fetal liver cells. Medium conditioned by other mouse tissues stimulated only granulocyte‐macrophage colony formation and this activity was not increased by the addition of pokeweed mitogen. Spleen cells stimulated by mixed leucocyte culture or concanavalin‐A had a weak capacity to stimulate erythroid colony formation.Production of the factors stimulating the four types of hemopoiesis was T‐lymphocyte dependent and nu/nu spleen cells were inactive. Factor production was also dependent on adherent cells but evidence from rat‐mouse combinations suggested that the T‐lymphocytes actually produced the active factors.Production of the four types of colony stimulating factors was radiosensitive (D0120–238 rads) and spleen cell populations of lighter buoyant density than 1.075 g/cm3 and sedimenting at 3.5–5.0 mm/hour were able to produce active conditioned media. Fractionation experiments failed to segregate spleen populations able to produce only one of the four stimulating factors.Production of factors stimulating hemopoiesis by mitogen‐stimulated lymphoid populations could be a process contributing to the control of hemopoiesis in vivo.
Erythroid stem cells in friend‐virus infected mice
Authors: Opitz Uta , Seidel Hans‐Joachim , Bertoncello Ivan 
Published: February 2005

AbstractThe erythropoietic stem cell compartment was studied in Friend‐virus (polycythemic strain, FV‐P) infected DBA/2 and NMRI mice with the CFUE and BFUE technique. Early after infection there was a depression in CFUE number in bone marrow and spleen, followed by an increase of the CFUE concentration, earlier and more pronounced in the spleen than in the marrow. Three days after FV‐P infection an erythropoietin (Ep) independent CFUE population started to grow and replaced the normal Ep‐dependent population within 8 to 12 days. The shift to Ep independency was not gradual. CFUE colonies of FV‐P infected bone marrow cells were two to three times larger than control colonies after three days in vitro incubation.BFUE colonies increased in number during the first days of infection, but were totally lost after more than ten days. After velocity sedimentation of bone marrow cells of FV‐P infected animals, however, the BFUE containing fractions showed normal BFUE colony growth and normal Ep sensitivity. In unfractionated bone marrow cell cultures BFUE colony growth could be observed later than ten days post infection when the cultures were refed with medium. It was therefore concluded that the loss of BFUE colony growth after FV‐P infection was an in vitro artefact due to inadequate culture conditions.