bluuebunny/crossref_metadata_2025_split huggingface dataset:
A mammalian somatic “cell cycle” mutant defective in G1
Authors: Michael Liskay R. 
Published: February 2005

AbstractVariants or “mutants” temperature‐sensitive (ts) for growth have been isolated by selection from a near‐diploid mouse cell line. Thus far. 10 ts mutants which grow normally at 33° C, but not at 39° C, have been isolated. These ts mutants were then studied to determine if any manifested their defect at a unique point or stage in the cell cycle. This type of ts mutant is termed a “cell cycle” mutant.The first screen involves observing individual cells of an asynchronous culture for residual division after a shift from 33° C (permissive temperature) to 39° (nonpermissive temperature). A cell cycle mutant should show some fraction of the cells dividing only once at a normal rate after the shift. The ts variant B54 met this first criterion for a cell cycle mutant (i.e., 50% residual division) and was further analyzed.The second screening technique monitors (1) the rate of entry into S, (2) the length of G2, and (3) the rate and duration of cells entering mitosis after a shift of an asynchronous culture to 39°. This experiment with B54 revealed that cells in G1 at the time of the shift to 39° failed to enter S while cells already into S completed the cycle at 39°. These results suggest that B54 is defective in a G1 function which is required for entry into S, but which is no longer needed once cells have entered S. Other results are presented which also support this hypothesis.In addition the ts function of B54 is apparently required for recovery from a “high density” G1 arrest.
The negatively charged protein extracted from Tetrahymena pyriformis as an attractant in Amoeba proteus chemotaxis
Authors: Nohmi Mitsuo , Tawada Katsuhisa 
Published: February 2005

AbstractWe extracted a pure protein from Tetrahymena pyriformis as the chemotactic substance in Amoeba proteus. The protein was heat‐stable, negatively charged at neutral pH (since its isoelectric point was near pH 4.5) and composed of three subunits. Its molecular weight was 3 × 8,000.
Flow microfluorometric studies of lectin binding to mammalian cells II. Estimation of the surface density of receptor sites by multiparameter analysis
Authors: Steinkamp John A. , Kraemer Paul M. 
Published: February 2005

AbstractA flow‐system multiparameter cell analyzer that simultaneously measures and processes fluorescence and cell volume signals from single cells was used to study the binding of fluorescein‐conjugated Concanavalin A (Con A–F) to the cell surface. Cells reacted with Con A–F were passed through a flow chamber where sensors measured both cell volume and fluorescence of each individual cell. Sensor signals were electronically processed by first converting the cell volume signals to two‐thirds power (proportional to surface area) and then forming the fluorescence‐to‐surface area ratio. These ratios, which were considered as estimates of the surface density of binding sites, were displayed as frequency distribution histograms using a multichannel pulse‐height analyzer for various cell populations differing in cell size. Comparisons between cell lines showed characteristic differences in binding site density. Cell cycle dependent changes were not found for CHO cells synchronized by mitotic selection. An important benefit of this analysis method was the ability to quantitate very weak cell surface fluorescence.
Myonemal contraction of Spirostomum I. Kinetics of contraction and relaxation
Authors: Hawkes R. B. , Holberton D. V. 
Published: February 2005

AbstractA microphotometric method is introduced that allows measurement of the contraction‐relaxation kinetics of Spirostomum in response to electrical stimulation. The time course of contraction includes a rapidly contracting phase of some 4–5 mS during which cells shorten at a rate in excess of 100 cell lengths sec−1. While a stimulus strength‐duration curve determines the threshold of the response, the response to above threshold stimuli of different strengths and to trains of stimuli suggest that contraction of Spirostomum may not be an all‐or‐none event. The kinetics of relaxation following high stimulating voltages and repetitive after contractions also induced by high voltages are explained by excitation‐contraction coupling through a stimulus‐dependent intermediate effector, possibly the release of calcium ions. Changes in resting membrane potential detected by intracellular recording do not influence the initiation of contraction, while microinjection of calcium buffers above 10−5 M Ca2+ invariably induces contraction.
Role of pH in fibroblast proliferation
Authors: Froehlich Jeffrey E. , Anastassiades Tassos P. 
Published: February 2005

AbstractSecondary cultures of human diploid fibroblasts were used to study the effect of pH on cellular proliferation. In nonconfluent cultures, the growth rate at pH 7.1 was similar to that at pH 7.7 regardless of serum concentration. However, the saturation density achieved at pH 7.7 at any serum concentration was always 2–4 times that achieved at pH 7.1, although the greatest differences in saturation density were observed at the higher serum levels. The results suggest that the effect of pH on saturation density is due to two factors. One, cells at pH 7.1 seem to have a greater ability to undergo contact‐inhibition than at pH 7.7, independent of any serum functions; and, two, confluent cells in medium at pH 7.1 are somewhat less sensitive to growth stimulation by increasing serum concentration than are confluent cells raised in medium at pH 7.7.
A temperature‐sensitive cell cycle mutant of the BHK cell line
Authors: Burstin Stuart J. , Meiss Harriet K. , Basilico Claudio 
Published: February 2005

AbstractA temperature‐sensitive growth mutant derived from the BHK 21 cell Line, ts AF8, was found to have greatly reduced DNA synthesis at the nonpermissive temperature. This reduction is mainly due to a decrease in the frequency of cells synthesizing DNA. Upon shift up, ts AF8 becomes blocked in the G1 phase of the cell cycle. The cells acquire elevated cAMP levels and a unimodal distribution of DNA content, equivalent to that of G1 cells at the permissive temperature, Ts AF8 cells blocked at the G1/S boundary with hydroxyurea will enter S when shifted to the nonpermissive temperature. On the other hand, ts AF8 cells arrested m G1 by serum deprivation and shifted to the nonpermissive temperature at the moment of serum addition do not enter S, while those synchronized by isoleucine deprivation and shifted at the time of isoleucine addition will enter S. These data suggest that the cycle arrest point of the ts AF8 mutation is located in G1 between the blocks induced by serum starvation and isoleucine deprivation.The reduction in DNA synthesis caused by the ts AF8 mutation is not reversed by infection or transformation with Polyoma virus. Mitochondrial DNA continues to be synthesized at wild‐type levels at the nonpermissive temperature.
The distribution of pyridine nucleotides between nucleus and cytoplasm
Authors: Rechsteiner Martin 
Published: February 2005

AbstractFollowing enucleation of a portion of human culture cells containing 3H‐pyridine nucleotides, autoradiography revealed no difference in the grain density over enucleated and whole cells. These results provide evidence that the concentration of pydine nucleotides does not differ by more than threefold between nucleus and cytoplasm and probably does not vary at all.
Synthesis of glycolipids and phospholipids in hamster cells: Dependence on cell density and the cell cycle
Authors: Hirschberg Carlos B. , Wolf Barbara Anne , Robbins P. W. 
Published: February 2005

AbstractSakiyama et al. ('72) reported the isolation of a line of hamster cells (NIL 1c1) which contains only three glycolipids, hematoside, ceramide monohexoside and ceramide dihexoside. The incorporation of radiolabeled palmitate into hematoside during 24 hours was three fold higher in normal confluent, non growing cells than sparse, growing ones. Polyoma transformed cells did not exhibit this effect.We have continued studies with the untransformed cell line and have found that the higher incorporation of radiolabeled palmitate into hematoside by normal confluent cells is not due to a higher rate of turnover of hematoside at confluence but represents a true chemical increase. We have also found that this increase is not a gradual process during cell growth but instead occurs only when the cells become confluent and stop growing. The increase of hematoside at confluence is not due to a higher rate of synthesis of hematoside during G1, relative to the other phases of the cell cycle. We found the rate of synthesis of hematoside to be constant throughout the cell cycle.The rate of synthesis of phosphatidyl choline, phosphatidyl ethanolamine, phosphatidyl serine, phosphatidyl inositol and sphingomyelin was also studied as a function of the cell cycle. We found no large differences in the synthetic rate of any given phospholipid species throughout the cell cycle although the rate of synthesis of the glycerophospholipids was somewhat higher during late G1 and S. We did, however, find major differences in the rates of synthesis of the different phospholipid species.
Synthesis of glycolytic and peroxisomal enzymes in Tetrahymena following a change in culture conditions
Authors: Levy Michael R. 
Published: February 2005

AbstractThe specific activity of a peroxisomal enzyme, lactate oxidase, and of pyruvate kinase and lactate dehydrogenase, which are not peroxisomal, increased rapidly when shaken cultures of Tetrahymena were transferred to conditions of oxygen restriction and supplemented with glucose. Two other peroxisomal enzymes, catalase and TPN‐linked isocitrate dehydrogenase, did not increase substantially, nor did succinate dehydrogenase. The increases were reduced if glucose was not added at the time of transfer, and were prevented by actinomycin D or cycloheximide, but not by chloramphenicol. The results suggest an involvement of peroxisomes in the metabolism of glycolytic endproducts when the availability of oxygen to the cell is limiting.
Slow phase hemolysis in hypotonic electrolyte solutions
Authors: Chan T. K. , Lacelle P. L. , Weed R. I. 
Published: February 2005

AbstractWhen a population of erythrocytes is partially hemolyzed the time course of hemolysis can be divided into a fast phase and a slow phase. The slow phase occurs with both rapid and gradual addition of the hypotonic medium (rapid and gradual hemolysis). There is no difference in the osmotic fragility of erythrocytes remaining at 60 minutes after rapid or gradual hemolysis.Erythrocytes near their critical hemolytic volume have an equimolar ouabain‐insensitive sodium‐potassium exchange. Critical non‐hemolytic swelling with resulting stress on the membrane appears requisite to slow phase hemolysis since more non‐penetrant sucrose is required to prevent slow phase lysis rather than that which would be predicted from the intracellular colloid osmotic pressure due to hemoglobin. Sucrose protection from slow phase hemolysis thus depends not only on counter‐balancing the colloid osmotic pressure, but also removal of sufficient intracellular water to prevent critical membrane strain. This model is consistent with that proposed by Katchalsky.Irreversible membrane changes associated with hypotonic stress manifested by persistent stomatocytic shape change and membrane wrinkling on return of cells to isotonicity appear to be due to critical changes in membrane components. Such cells, having normal indices and specific gravity are less deformable than control cells in 2.8 μm pore size polycarbonate filters.
Effect of chloramphenicol on replication of mitochondria in Tetrahymena
Authors: Gleason Florence K. , Ooka Mary P. , Cunningham William P. , Hooper Alan B. 
Published: February 2005

AbstractTetrahymena pyriformis ST (3 × 104 cells/ml) was treated with 0.1 mg/ml chloramphenicol (CAP). Cell division ceased after 1.5 divisions with no decreased viability. Total mitochondrial volume and succinic dehydrogenase (SDH) activity/liter increased 1.7‐fold and 3‐fold, respectively. SDH activity/cell decreased whereas malate dehydrogenase activity/cell and respiratory control ratios and P: O ratios of isolated mitochondria were unchanged in treated cells. During 12 hours of growth in CAP the total surface area of mitochondrial inner and outer membrane was essentially unchanged or increased 4‐fold, respectively. Mitochondria from cells treated with chloramphenicol had decreased size, buoyant density and protein: lipid ratio in the membranes. The membrane ubiquinone: protein ratio was unchanged.Tetrahymena cells contained 3.6 × 10−12 g of mitochondrial DNA and 6,800 mitochondria in a volume of 41,000 μ3. A 4‐hour treatment with CAP caused a 4‐fold increase in the number of mitochondria/cell and a 10‐fold increase in mitochondria/liter in contrast to a 4‐fold increase in number of mitochondria/liter in control cells. Thus CAP stimulated division of mitochondria. Individual mitochondria of treated cells had one‐tenth the volume of control mitochondria. The rate of increase of mitochondrial DNA/liter was the same in control and CAP‐treated cultures. The amount of DNA/mitochondrion decreased 75% in CAP‐treated cells due to the rapid division of mitochondria. The cell volume, cell protein content and mitochondrial DNA content/cell decreased with growth of control cultures.
Influence of mono‐ and multivalent cations on the electrokinetic properties of Rana pipiens kidney cells
Authors: Kiremidjian L. , Stotzky G. 
Published: February 2005

AbstractChanges in the cation composition of the ambient cell environment, at constant ionic strengths, altered the electrokinetic properties of the surface of normal adult Rana pipiens kidney cells in a manner which reflected more the physiochemical properties and binding affinities of the cation than its valence. The effect was expressed in the changes of the magnitude of the net surface charge, at any pH, and in the shift of the isoelectric point of the cell surface.
Variant HeLa cells selected for their resistance to ouabain
Authors: Rosenberg Howard M. 
Published: February 2005

AbstractThe cardiac glycoside, ouabain, normally kills HeLa cells at concentrations of about 10−7 m or greater. By treating a population of HeLa cells with increasingly higher concentrations of the drug, a variant population was obtained of HeLa cells capable of growing in medium containing 10−4 M ouabain.Inhibition of volume regulation of cells subjected to hypotonic shock was used as a measure of inhibition of active transport of Na across the plasma membrane. In that way dose‐response curves for the rapid effects of ouabain and other inhibitors of active Na transport were obtained with both the original, ouabain‐sensitive (OS) and the variant, ouabain‐resistant (OR) cells. Three other cardiac glycosides (digoxin, digitoxin and hellebrin) and two aglycones (digitoxigenin and strophanthidjn) were found to be equally as effective as ouabain in inhibiting volume regulation of the OS cells; the concentration which produced half‐maximum inhibition, I(max/2), was about 6 × 10−7 M in each case.Similar inhibition of the OR population by ouabain was observed only when the concentration exceeded 10−4 m [I(max/2)∼2.5 × 10−4 m], and the other steroid compounds had no effect on the variant cells at the highest concentrations tested (∼2 × 10−5 m). OR and OS cells differed also in their sensitivities to the cardioactive erythrophleum alkaloid, coumingine; I(max/2) for OS and OR cells was 5 × 10−8 m and 6 × 10−7 M, respectively.These results, in addition to results of ouabain binding experiments and measurements of the rates of reversal of inhibition of volume regulation, suggest that a major reason for the differential sensitivities of the two phenotypes to these drugs is different affinities of their sodium pumps for inhibitors of active transport.
Characterization of the ATP‐phosphohydrolase activity of bovine spermatozoa flagellar extracts
Authors: Young Leona G. , Smithwick Eleanor B. 
Published: February 2005

AbstractThe ATP‐phosphohydrolase activity of extracts prepared from bovine spermatozoa flagella (BSFE), was characterized with respect to enzyme, substrate, activator ion and salt concentration, temperature dependence and time stability. BSFE required the presence of a divalent cation for activity: Mg++ or Ca++ could function as activator; Mn++, Zn++ and Cd++ could not. EDTA, but not EGTA, was inhibitory to enzymatic activity. Ca++ inhibited the Mg++ stimulated activity. ATP was dephosphorylated more rapidly than GTP>CTP>ITP, and ADP was dephosphorylated at 40% of the rate of ATP. The magnesium activated ATPase was stimulated by potassium and inhibited by sodium ions. Activation of BSFE ATP‐phosphohydrolase was maximal in the presence of Mg++ and ATP in equimolar concentrations and K+ (0.05–0.3 m) at 30°C. Although the enzymatic activity of the extract was found to decrease rapidly with time, it could be maintained for up to three days by the addition of 2‐β‐mercaptoethanol to the bovine spermatozoa flagellar extracts.
Exposure of an arginine‐rich protein at surface of cells in S, G2, and M phases of the cell cycle
Authors: Stein Sylvia M. , Berestecky John M. 
Published: February 2005

AbstractPhenylglyoxal (PG) is shown to be a cell surface probe specific for arginine moieties in protein: (1) It does not enter the cell as evidenced by lack of PG in the cytoplasm. (2) It does not cause excessive cell leakage as measured by release of 51Cr. (3) It reacts with positively‐charged groups in proteins at the cell surface but not with those of phospholipids at the surface; since pronase removes PG from the surface, but phospholipase C does not. (4) Under the conditions used in these experiments, it reacts virtually exclusively with arginine moieties in protein (Freedman et al., '68; Takahashi, '68; Werber and Sokolovsky, '72).Synchronized cells were exposed to radioactive PG to assess quantity of arginine moieties in protein at the surface. There is a sharp decrease in arginine at the cell surface at entry into G1 phase from M and a 24‐fold increase upon entry into S phase. There is a slight drop in exposed arginine in late S phase followed by an increase to 26 times the G1 level immediately prior to mitosis. Lactoperoxidase‐catalyzed iodination of tyrosine moieties in protein at the surface of synchronized cells shows a very gradual increase in protein as the cells move through the cycle and increase in size. Since the increase in arginine moieties in protein at the surface does hot reflect a similar increase in total protein at the surface, an arginine‐rich protein appears to be exposed at the cell surface during the division‐related phases of the cell cycle.
Requirement of bromodeoxyuridine for the maintenance of “transformed” characteristics in bromodeoxyuridine dependent cells
Authors: Horn Diane , Davidson Richard L. 
Published: February 2005

AbstractA bromodeoxyuridine (BUdr) dependent cell line, called B4, which requires BUdr not only for optimal growth but also for the maintenance of the non‐contact inhibited state was described previously. We have now shown that contact inhibition in the B4 cells in the absence of BUdr is associated with a marked decrease in the percent of cells synthesizing DNA. The transition to the contact inhibited state in the absence of BUdr does not seem to be due to changes in cyclic AMP levels. It has also been shown that several but not all of the characteristics which distinguish transformed from untransformed cells also distinguish B4 cells grown in the presence of BUdr from B4 cells grown in the absence of BUdr. In addition to being contact inhibited, B4 cells grown in the absence of BUdr have a higher serum requirement, grow less well in soft agar, and are less agglutinable by wheat germ agglutinin than B4 cells grown in the presence of BUdr. Agglutinability by concanavalin A, however, is the same for B4 cells grown in the presence and absence of BUdr. Dependent cells maintained in the presence of BUdr do not form tumors and it is not yet clear how the transformed characteristics of the dependent cells are related to malignancy.
The pattern of density dependent growth inhibition in murine fibroblasts
Authors: Canagaratna Mary C. P. , Riley P. A. 
Published: February 2005

AbstractObservations on the pattern of nuclear incorporation of 3H‐TdR in long term (8‐day) and short term (3‐day) 3T3 cultures with local cell densities between 0.2 × 104 and 6.2 × 104 cells/cm2 are reported. Contrary to a number of previous studies our observations indicate that density dependent inhibition is exhibited in relatively sparse cultures, commencing at 0.5 × 104 cells/cm2. Various possible mechanisms which could have caused the observed pattern of density‐dependent regression in labelling index are discussed.
Glutamine synthetase activity in WI‐38 cells
Authors: Viceps Dace , Cristofalo V. J. 
Published: February 2005

AbstractIn the presence of complete growth media (Eagle's MEM), human diploid WI‐38 cells have a low level of glutamine synthetase activity. The activity could be increased by depriving the cells of exogenous glutamine; addition of hydrocortisone to either glutamine‐deficient or complete medium had no effect on the activity of the enzyme. Cell growth ceased under conditions that enhanced glutamine synthetase activity, and hydrocortisone could not reverse this inhibition.
Studies on the regulation of the three enzymes of the leloir pathway in cultured mammalian cells. I. Effect of substitution of galactose for glucose as the sole hexose in the medium in human diploid cell strains and in a rat hepatoma line
Authors: Stern Elizabeth Sell , Krooth Robert S. 
Published: February 2005

AbstractIn human diploid cell strains, the substitution of galactose for glucose as the sole hexose in the medium had no measurable effect on the specific activity of the cell protein for any of the three enzymes of the Leloir pathway. These enzymes are galactokinase, α‐D‐galactose‐1‐phosphate:UDP glucose uridylyl transferase and UDP galactose 4‐epimerase. A cell strain from a patient with galactosemia had no detectable activity for the transferase. The substitution of galactose for glucose in the medium of these cells (which has been shown to cause the cells to accumulate galactose‐1‐phosphate) also failed to affect cellular activity for the three enzymes. Similarly, the three activities failed to respond to the substitution of galactose for glucose in cultures of a rat hepatoma line. Cells of this line have been shown by others to perform a number of the tissue‐specific functions of liver.The failure of galactose to stimulate increased cellular activity for the three enzymes represents a striking difference between the behavior of these enzymes in human diploid cell strains and their behavior in E. coli.
Induction of hyaluronic acid synthetase activity in rat fibroblasts by medium change of confluent cultures
Authors: Tomida Mikio , Koyama Hideki , Ono Tetsuo 
Published: February 2005

AbstractHyaluronic acid synthesis in cultured cells usually occurs during the growth phase. The relation between hyaluronic acid synthetase activity and cell proliferation is studied. The synthetase activity in rat fibroblasts is high during the growth phase, but low in the stationary phase. When the old medium of stationary cultures is renewed with fresh medium containing 20% calf serum, DNA synthesis occurs synchronously between 12 and 20 hours, followed by cell division. Under these conditions, the hyaluronic acid synthetase activity is significantly induced within two hours, reaching a maximum level at 5–8 hours, and then decreases gradually. This induction of the synthetase, which shows a high turnover rate, requires continued synthesis of both RNA and protein. Furthermore, the induction of both DNA and hyaluronic acid synthesis is found to be caused by calf serum added in the medium. However, dialysis and ultrafiltration of the serum permit us to concentrate an active fraction with a high molecular weight, which induces the synthetase activity, but not DNA synthesis.