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  • 1
    Electronic Resource
    Electronic Resource
    The Uptake of Pyrimidine Nucleosides in Tetrahymena. I. Uridine (1976)
    Oxford, UK : Blackwell Publishing Ltd
    The @journal of eukaryotic microbiology 23 (1976), S. 0 
    Details
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SYNOPSIS. Uridine uptake was examined in Tetrahymena pyriformis GL-7 in defined medium under conditions where food vacuole formation is not a significant factor in solute acquisition by the cell. The results indicate the presence of a saturable mechanism which follows Michaelis-Menten kinetics. When corrected for diffusion the apparent Km for the carrier is 2.3 ± 0.6 μM and the Vmax is 7.3 ± 0.2 × 10−7 nmoles/cell/min. It is evident from nucleotide pool analysis that most of the radioactivity of externally supplied [3H]uridine appears in UMP with the remainder in UTP. Uridine is apparently phosphorylated immediately upon entry into the cell and neither uridine-cytidine kinase activity nor RNA synthesis are rate-limiting in the uptake process. Uridine transport is competitively inhibited by a variety of ribo- and deoxyribonucleosides as well as several nucleoside analogs. Neither uracil nor ribose or deoxyribose are effective inhibitors of uridine transport indicating the carrier is specific for the nucleoside. There is little difference between the Ki values for ribo- as opposed to deoxyribonucleosides except in the case of deoxyguanosine which is much less effective as an inhibitor under the conditions of this study, than all the other nucleosides, including guanosine.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1550-7408.1976.tb03814.x
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    The Effects of Temperature and Heavy Water on Cell Division in Heat-Synchronized Cells of Tetrahymena (1972)
    Oxford, UK : Blackwell Publishing Ltd
    The @journal of eukaryotic microbiology 19 (1972), S. 0 
    Details
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SYNOPSIS. A study was undertaken of the rates of cell division of heat-synchronized cells of Tetrahymena pyriformis GL at various temperatures in water and 20, 30 and 40% heavy water. The results suggest that division rate is limited by a protein which undergoes both high and low temperature denaturation and that this protein is partially stabilized against heat-denaturation while becoming more susceptible to cold denaturation in the presence of heavy water. Thus, the optimum temperature for division shifts upward as the heavy water concentration is increased, with a maximum shift of 1 C occurring in 40% heavy water. In addition, division activity occurs in heavy water at 34 C, a temperature at which cells kept in water are blocked. Furthermore, the sharp increase in slope seen in the low temperature portion of Arrhenius plots of the data, occurs at higher temperatures when heavy water is present. Finally, at virtually all temperatures, except the highest, heavy water has a depressive effect on division rate indicating a general inhibitory influence of deuterium-substituted water on rate processes within the cell.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1550-7408.1972.tb03484.x
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  • 3
    Electronic Resource
    Electronic Resource
    RNA Synthesis and Cell Division in Heat-Synchronized Populations of Tetrahymena pyriformis (1965)
    Oxford, UK : Blackwell Publishing Ltd
    The @journal of eukaryotic microbiology 12 (1965), S. 0 
    Details
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SYNOPSIS. The incorporation of H3-uridine during the pretransition period of heat-synchronized cells of Tetrahymena pyriformis occurs in two peaks, one at 20 and the other at approximately 40 min following the end of the last synchronizing heat treatment (EH). Although Actinomycin D tends to produce substantial inhibition of both peaks it has a significant effect on cell division only if applied before or during the first peak of incorporation. It appears that the production of new RNA is required for the first synchronous division and that it is synchronized with the division process. Actinomycin D seems to increase, slightly, the degree of incorporation of H3-uridine into RNA when applied at 0 and 10 min past EH. This effect may be correlated with the positive excess delays of division which result when cells are exposed to the inhibitor at these times. A similar effect of Actinomycin on incorporation at 30 or 40 minutes past EH, however, does not appear to be associated with any strong effects of the inhibitor on division.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1550-7408.1965.tb03249.x
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  • 4
    Electronic Resource
    Electronic Resource
    RNA synthesis and cell division in cold-synchronized cells of Tetrahymena pyriformis (1966)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 67 (1966), S. 217-223 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Cells of Tetrahymena pyriformis have been cold-synchronized using a repetitive cycle of six, two-hour cold shocks (9.5°C) alternating with decreasing periods (60-30 minutes) at 28°C. This system gives a maximum division index of 70-80% occurring at 90 minutes from the end of the last synchronizing cold-treatment (EC). Examination of the division sensitivity of these cells to actinomycin D applied continuously at ten-minute intervals from EC reveals that division is essentially blocked until approximately 40 minutes past EC, after which a rapid decrease is sensitivity to the inhibitor occurs. Coinciding with this period of high sensitivity is the occurrence of a peak of C14 uridine incorporation at 40 minutes past EC. Inhibition of this peak is correlated with an inhibition of division, whereas strong inhibition of RNA synthesis beyond 60 minutes past EC has little effect on division activity. The similarity of these findings with those of the heat-synchronized system is discussed with the suggestion that both heat- and cold-synchronizing treatments result in the synchronous resynthesis of a division-associated fraction of RNA.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1040670203
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  • 5
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    RNA synthesis and cell division in cold-synchronized cells ofTetrahymena pyriformis (1966)
    Wiley
    Details
    Publication Date: 1966-04-01
    Print ISSN: 0021-9541
    Electronic ISSN: 1097-4652
    Topics: Biology , Medicine
    Published by Wiley
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