bluuebunny/crossref_metadata_2025_split huggingface dataset:
Plasma membrane ectoglycosyltransferase activity of L1210 murine leukemic cells
Authors: Bernacki R. J. 
Published: February 2005

AbstractL1210 murine leukemia cells after treatment with Cl. perfringens neuraminidase at pH 7.0 incorporated six times more N‐acetylneuraminic acid‐[C14] than control cells when incubated for 30 minutes with cytidine 5′‐monophosphate N‐acetylneuraminic‐[C14] acid and three times more galactose‐[C14] when incubated with uridine diphosphate galactose‐[C14]. These sugars were incorporated in a 10% trichloracetic acid insoluble fraction and more than 75% of the incorporated N‐acetylneuraminic acid‐ [C14] could be removed by further treatment of these cells with neuraminidase. The incorporation of N‐acetylneuraminic acid‐ [C14] as a function of time was divided into two rates: a rapid one, active during the first 30 minutes followed by a slower one, similar to the rate observed with untreated cells. The addition of Ba++ and Ca++ ions at 8.3 mM increased the incorporation of N‐acetylneuraminic acid‐ [C14] by 25% while 8.3 mM EDTA decreased activity by 58% . The addition of Zn++ or Hg++ at similar concentrations abolished the incorporation almost completely. The optimal pH for the incorporation of N‐acetylneuraminic acid‐ [C14] by these neuraminidase treated cells was 6.5. These data suggest that ectoglycosyltransferases are present on the outer surface of the plasma membrane of L1210 cells and are able to catalyze the addition of radiolabeled nucleotide sugars onto macromolecular acceptors (cell surface glycoproteins and glycolipids) prepared by prior incubation of the cells with neuraminidase. Use of these procedures for labeling outer cell surfaces may also prove to be valuable for the study of plasma membrane glycoprotein and glycolipid structure, synthesis, and turnover.
Studies on a chinese hamster line that is temperature sensitive for the commitment to DNA synthesis
Authors: Smith B. J. , Wigglesworth N. M. 
Published: February 2005

AbstractThe Chinese hamster cell line K12 is temperature sensitive for the initiation of DNA synthesis and for the programming of rounding up to enter mitosis. Viability is lost expontentially after twelve hours at the non‐permissive temperature. This temperature sensitivity is reversed following exposure of K12 cells to SV40 virus.
Dynamic osmotic behavior of chick blood lymphocytes
Authors: Doljanski F. , Ben‐Sasson S. , Reich M. , Grover N. B. 
Published: February 2005

AbstractThe dynamic response of chick blood lymphocytes to hypotonic shock is investigated using electrical sizing techniques, and an attempt is made to characterize the mechanisms involved. The cells first swell rapidly, as expected, but then gradually return to their initial volume. Maximum volume is attained in 2 minutes and the return is complete within about 15 minutes at room temperature. This cycle is studied under different osmotic strengths, temperatures, and cation compositions; behavior following successive hypotonic and hypertonic shocks is also described. Metabolic inhibitors are shown to have no effect, even at relatively high concentrations, while ouabain (10−3 M) affects only the much slower second‐order return process that sets in when the main one is blocked by appropriate external cation concentration.It is proposed that a large increase in membrane permeability to K+ occurs as the cell swells beyond its iso‐osmotic volume, but none to Na+. The experimental results are then explained by ascribing the swelling to water entering the cell until the osmotic pressure inside equals that outside, and the return phase to the electrochemical potential gradient for K+ forcing it out of the swollen cell together with the associated anion and water in proportions that preserve osmotic equilibrium. This latter is a non‐active process independent of Na+ whose direction can be reversed by using K+ as the cation in the external medium.The existence in the literature of several related observations is pointed out and some of the implications of our findings are discussed briefly in terms of a corrugated membrane structure.
Release of cytoplasmic enzymes into culture fluid
Authors: Nose Kiyoshi , Nitta Keiko , Takaoka Toshiko , Katsuta Hajim 
Published: February 2005

AbstractThe release of enzymatic activities from cells grown in protein‐and lipid‐free synthetic media into culture fluids was investigated. Cell strains employed were the derivatives from mouse fibroblasts, rat liver parenchymal cells, rat ascites hepatoma cells and HeLa cells. Activities of acid DNase, acid RNase and alkaline phosphatase (ALP)‐I were detected in culture fluids as early as one day after renewal of medium, whereas those of β‐glucuronidase and acid phosphatase were not found. This release of enzymes was unlikely to be caused by cell disruption during cultivation.The release of Dnase was inhibited by the addition of cycloheximide or actinbomycin D, whereas that of ALP‐I was not inhibited.
Factors affecting division rhythmicity in Euglena gracilis
Authors: Cook J. R. 
Published: February 2005

AbstractIn phototrophic culture of Euglena gracilis, good synchrony was found only under rather restricted programs of light‐dark cycles, and rather narrow ranges of temperature and light intensity, when cultures were flushed with air fortified with adequate amounts of CO2. When flushed with air alone, CO2 was found to be limiting, and while cell divisions were rhythmic, less than a doubling of cell number occurred in division bursts. With air as gas phase, rhythmic division activity was maintained over wide ranges of temperature, light intensity, and the ratio of light:dark in a given program; all these factors affected the amplitude of the division burst, however.
In vitro response of goldfish (Carassius auratus L.) dermal melanophores to cyclic 3, 5′‐nucleotides, nucleoside 5′‐phosphates and methylxanthines
Authors: Abramowitz Joel , Chavin Walter 
Published: February 2005

AbstractcAMP, dbcAMP, cCMP, cGMP, theophylline and caffeine caused reversible melanosome dispersion within 5 minutes at 10 mM in the dermal melanophores of the black goldfish, Carassius auratus L. cTMP, cUMP, 5′‐AMP, 5′‐CMP, 5′‐GMP, 5′‐TMP, and 5′‐UMP did not produce melanosome dispersion or aggregation in this melanophore system. cAMP was the most effective nucleotide in the induction of melanosome dispersion; at 10 mM, cGMP and at 5 mM, dbcAMP were the least effective of those nucleotides inducing melanosome dispersion. At the 10 mM level dbcAMP required 30 minutes to evoke the same degree of melanosome dispersion as 5 minutes cAMP treatment. Theophylline was more effective than caffeine in eliciting melanosome dispersion. At 1 mM, theophylline and caffeine first induced melanosome dispersion which was followed by aggregation in the course of the 30 minute test period. These reactions suggest both a high melanophore phosphodiesterase activity and competitive inhibition of phosphodiesterase by theophylline and caffeine. Induction of melanosome dispersion by several cyclic 3′,5′‐nucleotides suggest multi‐nucleotide control of melanosome dispersion. These findings also support a proposed mechanism of prostaglandin induced melanosome dispersion as well as the “second messenger” hypothesis.
Effect of cAMP on nucleoside metabolism II. Cell cycle dependence of thymidine transport
Authors: Roller Barbra A. , Hirai Kanji , Defendi Vittorio 
Published: February 2005

AbstractWe have shown previously that adenosine 3′5′ cyclic monophosphate (cAMP) increased the transport of thymidine into monkey cells (CV‐1) without affecting DNA synthesis (Roller et al., '74). Using techniques of cell synchronization, cell separation and DNA synthesis inhibitors in CV‐1 and other cell lines, we now report that thymidine transport at low thymidine concentrations increases during the S phase of the cell cycle and that initiation of DNA synthesis is necessary for thymidine transport, although continuation of DNA synthesis is not necessary. Cyclic AMP alters nucleoside transport by increasing the Vmax for the transport reaction, but has no effect on the Km. Cyclic AMP is found not to affect the time in the cell cycle when thymidine transport occurs or the quality of the transport reaction, and only affects the amount of thymidine transported.
Heterogeneity of molecules with low molecular weight isolated from media conditioned by human leukocytes and capable of stimulating colony formation by human granulopoietic progenitor cells
Authors: Price G. B. , Senn J. S. , McCulloch E. A. , Till J. E. 
Published: February 2005

AbstractMolecules of low molecular weight, able to stimulate colony formation by human granulopoietic cells, were prepared from media conditioned by normal and leukemic human peripheral blood leukocytes. When molecules from these sources were studied, heterogeneity was observed in their ability, after radioiodination, to bind and suicide granulopoietic progenitors, in their radiolabelled tryptic digestion products and in their biological activity as stimulators of granulocyte colonies.
The biosynthesis and turnover of nicotinamide adenine dinucleotide in enucleated culture cells
Authors: Rechsteiner Martin , Catanzarite Valerian 
Published: February 2005

AbstractNicotinic acid mononucleotide (NaMN) and nicotinamide mononucleotide (NMN) have been proposed as intermediates in the biosynthesis of nicotinamide adenine dinucleotide (NAD) from nicotinic acid and nicotinamide respectively. Although NaMN and NMN were not detected in acid extracts from whole D98/AH2 cells following pulses with 3H‐nicotinic acid and 3H‐nicotinamide, they were observed following pulses of enucleated cells. Several experiments indicate that enucleated cells are incapable of synthesizing NAD and that biosynthesis stops with mononucleotide formation. These results provide support for the idea, based upon fractionation studies, that NAD pyrophosphorylase (which catalyzes the reaction NMN or NaMN + ATP → NAD or desamido‐NAD) is localized exclusively in the nucleus.Acid extraction and chromatography were also used to compare the stability of 3H‐NAD in enucleated and whole cells. In the presence of the glutamine analog, azaserine, the intracellular concentration of 3H‐NAD decreased exponentially with a half‐life of 4 hours in whole cells. In enucleated cells the intracellular concentration of 3H‐NAD decreased with a half‐life greater than 14 hours. The increased stability of NAD in enucleated cells was confirmed by autoradiography. These results demonstrate the key role of the nucleus in both the biosynthesis and turnover of NAD.
The origin of chicken hematopoietic colonies as assayed in semisolid agar
Authors: Dodge W. H. , Silva R. F. , Moscovici C. 
Published: February 2005

AbstractThis investigation was undertaken to determine whether primitive stem cells and/or fully differentiated macrophages were the source of in vitro colonies derived from hematopoietic tissues.The chicken colony‐forming cell (CFC) present in uncultured yolk sac was a nonadherent, presumably undifferentiated cell. The efficiency of colony formation in this case was approximately 0.08%. In contrast to uncultured yolk sac, the CFC present in one‐week old yolk sac cultures was evidently a macrophage. Yolk sac cultures, which consisted of greater than 99% macrophages, produced colonies with an efficiency of 1–5% while cultures derived from peritoneal macrophages produced colonies with an efficiency of 10%. Silica selectively destroyed macrophages and reduced the colony forming efficiency of cells derived from yolk sac cultures.
Mutants of Chinese hamster cells resistant to adenosine
Authors: McBurney Michael W. , Whitmore Gordon F. 
Published: February 2005

AbstractChinese hamster cells do not grow in medium containing high concentrations of adenosine because pyrimidine biosynthesis is inhibited. Adenosine metabolism was examined in two mutant cell lines isolated on the basis of resistance to adenosine. One line was deficient in adenosine kinase suggesting that high intracellular AMP concentrations may block pyrimidine synthesis indirectly in wild type cells by inhibiting PRPP synthetase. Although no enzymatic defect could be identified in the other cell line, these cells inefficiently utilize adenosine supplied in the medium.
Effect of leucine on the temperature sensitive phenotype of a mammalian leucyl‐tRNA synthetase mutant
Authors: Molnar S. J. , Rauth A. M. 
Published: February 2005

AbstractThe concentration of leucine in the growth medium has been found to influence the expression of the temperature sensitive phenotype of a mutant of Chinese hamster ovary cells with an altered leucyl‐tRNA synthetase. Plating efficiency and growth studies showed that increasing the leucine concentration allows cells to survive at normally non‐permissive high temperatures and conversely decreasing the leucine concentration enhances the adverse effects of high temperature. A similar but smaller effect was noted with isoleucine. It is suggested that this observation may form the basis of a rapid test, useful in directing the investigation of the lesion in similar mutants to pathways involving specific amino acids.
The effects of ouabain on the cell mitotic cycle of mouse lymphoblasts
Authors: Cuff Joyce M. , Lichtman Marshall A. 
Published: February 2005

AbstractThe inhibition of cell proliferation by ouabain has been analyzed with respect to the cell cycle. Three lines of evidence indicate that growth rate is modified by altering to different degrees the rate of progress through stages of the cell cycle: (1) a three hour lag occurs between the time of ouabain addition and the inhibition of proliferation; (2) ouabain must be present at least two to four hours prior to the mitotic burst of synchronized cells for inhibition of mitosis to occur; (3) parasynchrony is observed when cells are resuspended in ouabain‐free medium after 12 hours of exposure to ouabain.Analysis of the distribution of cells in each of the stages of the cell cycle at various times during ouabain treatment reveals a progressive increase in the fraction of cells in S with a concomitant decrease in the percent of cells in each of the other stages. These results indicate that the prolongation of the cell cycle time in the presence of ouabain is due primarily to an S stage block.
The effect of insulin on basal and hormone‐induced elevations of cyclic AMP content in cultured human fibroblasts
Authors: Rosenthal Judith W. , Goldstein Samuel 
Published: February 2005

AbstractStudies were carried out on confluent cultures of human fibroblasts to explore the effect of insulin on basal and hormone‐induced elevations of intracellular cyclic AMP content during short‐term incubations in serum‐free medium. Insulin tended to decrease basal levels of cyclic AMP but this was not statistically significant. Similarly, insulin was unable to block the elevations of intracellular cyclic AMP content induced by PGE1, epinephrine and glucagon. Paradoxically, when cells were preincubated with insulin, PGE1‐stimulated cyclic AMP elevation was potentiated, possibly because insulin was conserving factors needed for a maximal PGE1 stimulus or retarding the leakage of cAMP itself. The results indicate that insulin has little or no direct effect on cyclic AMP metabolism in cultured human fibroblasts and is consistent with the known insensitivity of these cells to insulin for other parameters.
Conditionally lethal mutations in Chinese hamster cells. Characterization of a cell line with a possible defect in the krebs cycle
Authors: Defrancesco L. , Werntz D. , Scheffler I. E. 
Published: February 2005

AbstractA variant Chinese hamster cell line has been isolated from a mutagenized population that has a markedly reduced ability to oxidize a variety of substrates via the Krebs cycle. The production of 14CO2 from 14C‐labeled compounds was measured using pyruvate, acetate, β‐hydroxybutyrate, palmitate and glutamate, and in all cases it was negligible in the mutant. In contrast to this, significant amounts of 14CO2 were produced from 14C‐aspartate and 14C‐succinate which suggests that some reactions of the Krebs cycle can take place and this conclusion is supported by tracer experiments with labeled compounds. The rate of respiration measured with a Clark oxygen electrode in the mutant was compared to several normal Chinese hamster cell lines and was found to be only 8%. Mitochondria appear to be present in normal numbers and with only minor differences in morphology. The measurement of difference spectra between oxidized and reduced states permits us to conclude that the cytochromes are all present and functional. These results lead us to believe that there may be a defect in the Krebs cycle between α‐ketoglutarate and succinate. Alternatively a defect in a structural component of the mitochondria or in the electron‐transport chain itself may be causing pleiotropic effects in the Krebs cycle and respiration.
Acetylcholine‐induced initiation of thymic lymphoblast DNA synthesis and proliferation
Authors: Macmanus J. P. , Boynton A. L. , Whitfield J. F. , Gillan D. J. , Isaacs R. J. 
Published: February 2005

AbstractLow (5 × 10−9 M to 10−7 M) acetylcholine concentrations cause a calcium‐independent stimulation of the initiation of DNA synthesis and proliferation of lymphoblasts which are part of rat thymocyte populations suspended in vitro. A much higher (5 × 10−5 M) acetylcholine concentration also stimulates lymphoblast DNA synthesis and proliferation, but this action is calcium‐dependent. This proliferogenic response to acetylcholine is however not clearly mediated by either cyclic GMP or cyclic AMP.
The effect of the herbicide 2,4,5 trichlorophenoxy acetic acid (245T) on the growth and metabolism of Tetrahymena pyriformis
Authors: Silberstein Gary B. , Hooper Alan B. 
Published: February 2005

AbstractThe herbicide 2,4,5 trichlorophenoxy acetic acid (245T) at concentrations from 0.5 to 0.9 mM, was found to inhibit respiration and then growth in exponentially growing cultures of Tetrahymena pyriformis. Cell division was stopped for periods up to 60 minutes after which the cells recovered and division resumed. Recovery of oxygen utilization and cell division occurred in the presence of 245T. 245T was shown to inhibit mitochondrial oxygen utilization. Mitochondria from cells that had recovered from 245T treatment lost their sensitivity to low concentrations of the herbicide and sedimented deeper in a sucrose gradient than mitochondria from control cells.
Differentiation of erythroleukemic cells in vitro: Irreversible induction by dimethyl sulfoxide (DMSO)
Authors: Preisler Harvey D. , Giladi Miriam 
Published: February 2005

AbstractThe inclusion of DMSO in the media of suspension cultures of Friend erythroleukemia cells results in the erythroid differentiation of these cells. The studies reported here were directed towards answering two questions: (1) How long an exposure to DMSO is necessary to induce the differentiation of these cells; and (2) What is the fate of the differentiating cells when DMSO is removed from the medium. Exposure to DMSO for less than 24 hours failed to produce any detectable evidence of erythroid differentiation. On the other hand, culture in the presence of DMSO for 24 hours followed by culture in DMSO‐free medium for four additional days produced a small but detectable increment in the proportion of benzidine positive cells in the culture. Once the differentiation of an individual cell was initiated, the process continued after removal of DMSO from the medium. The cell became progressively more differentiated as evidenced by increases in the intensity of benzidine staining as well as in the rate of heme synthesis and heme content. However, when cells which had been induced to differentiate by DMSO were cultured in DMSO‐free medium for more than 3–4 days, they became vacuolated and apparently died. This latter phenomenon, as well as the more rapid proliferation of the undifferentiated cells in the culture, accounts for the observation that when new cultures are established from cultures which have been grown in the presence of DMSO for several days, the culture which results ultimately contains only differentiated cells.
Incorporation of fucose and glucosamine into cell bound and medium released macromolecules
Authors: Herrmann Heinz , Havaranis Amalia S. , Doetschman Thomas C. 
Published: February 2005

Abstract(1) Determinations were carried out on the incorporation of fucose‐6‐[3H] and glucosamine‐6‐ [3H] into trichloracetic acid insoluble macromolecules which remained bound to the cells or were released into the medium of chick embryo muscle cell cultures. The radioactivity determined in the medium was corrected for unspecific binding of label to components of the medium. (2) During an incorporation period of six hours the incorporation per microgram DNA with fucose as label into cell bound macromolecules is about twice as high as the incorporation into macromolecules released into medium. With glucosamine about twice as much is incorporated into medium released than into the cell bound macromolecules. (3) The incorporation per microgram DNA increases during a culture period of three days but the increase ceases at different times during this culture period when determined with fucose or glucosamine or for cell bound and medium released material. (4) An increase in cell density increases the incorporation per DNA of fucose and to a much slighter extent that of glucosamine. Reduction of cell density by addition of cytosine arabinoside to the medium does not decrease the incorporation per microgram DNA. (5) The effect of changes of fibroblast/myoblast ratios on the incorporation of fucose and glucosamine were examined. No significant effect was observed for a ratio of 10–30% fibroblasts when control cultures or cultures after cell sedimentation were maintained in complete medium. Marked changes were observed after culture in medium without protein components. Under these conditions an increase in the fibroblast/myoblast ratios were observed as well as an increase in the incorporation of label into medium released and a decrease into cell bound macromolecules.
Myonemal contraction of spirostomum. II. Some mechanical properties of the contractile apparatus
Authors: Hawkes R. B. , Holberton D. V. 
Published: February 2005

AbstractIn several respects, notably the high velocity of shortening, Ca2+ dependence, and ATP independence, contraction of Spirostomum resembles the spasmonemal mechanism of the peritrich ciliates. In this report further mechanical properties of the contractile apparatus are described that extend this comparison. The velocity‐load characteristic is more appropriate to an elastomer than to a muscle where contraction force is load‐dependent. Active tension is found to relate linearly to cell length for extensions up to and beyond resting length (lr), an elastic limit is reached around 1.5 lr. At resting length this tension, measured by the deformation of a glass microbalance, is similar to that predicted from consideration of the hydrodynamic forces normally resisting shortening. The tension‐length relation for the unstimulated (passive) cell is also linear between lr and the elastic limit, but is displaced from the active tension‐length curve and is of reduced stiffness. Kinetic studies suggest that maximum tension and maximum velocity coincide. Calculations are presented that support a model of contraction in Spirostomum in which the myonemes behave as a mechanochemical engine powered directly by the chemical potential of Ca2+.