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  • 1975-1979  (5)
  • Life and Medical Sciences  (3)
  • Block-structured languages  (2)
  • 1
    Digitale Medien
    Digitale Medien
    On the time required for reference count management in retention block-structured languages. Part 2 (1978)
    Springer
    International journal of parallel programming 7 (1978), S. 91-119 
    Details
    ISSN: 1573-7640
    Schlagwort(e): Block-structured languages ; retention vs. deletion ; contour model ; stack model ; reference counts ; lifetime checks ; time estimates
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract In this paper, two implementations of generalized block-structured languages are presented and compared for time requirements. One implementation, the Lifetime Stack Model, implements the deletion strategy with lifetime checks; the other, the Partial Reference Count Contour Machine, implements the retention strategy. For a large subset of the lifetime well-stacking programs, those that run correctly on the first model, the two models are shown to require nearly the same order of magnitude of time. The use of full label values is shown to have a detrimental effect on the time efficiency of the latter model. Part 1, in Volume 7, Number 1, of this journal, gives a general description of the machines, some of their definitions, and proof of the results. Part 2, in this issue, serves as an appendix to Part 1 and contains most of the formal definitions of the machines.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00975882
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  • 2
    Digitale Medien
    Digitale Medien
    Time required for reference count management in retention block-structured languages. Part 1 (1978)
    Springer
    International journal of parallel programming 7 (1978), S. 11-64 
    Details
    ISSN: 1573-7640
    Schlagwort(e): Block-structured languages ; retention vs. deletion ; contour model ; stack model ; reference counts ; lifetime checks ; time estimates
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract In this paper, two implementations of generalized block-structured languages are presented and their time requirements compared. One implementation, the lifetime stack model (LSM), implements the deletion strategy with lifetime checks; the other, the partial reference count contour machine (PRCCM), implements the retention strategy. For a large subset of the lifetime well-stacking programs, which are precisely those that run correctly on the first model, the two models are shown to require nearly the same order of magnitude of time. The use of full-label values is shown to have a detrimental effect on the time efficiency of the latter model. Part 1, in this issue, gives a general description of the machines and part of their definitions, and proves the results. Part 2, in the next issue, serving as an appendix to Part 1, contains most of the formal definitions of the machines.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00991939
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  • 3
    Digitale Medien
    Digitale Medien
    The H+/site ratio of mitochondrial electron transport (1976)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 89 (1976), S. 595-602 
    Details
    ISSN: 0021-9541
    Schlagwort(e): Life and Medical Sciences ; Cell & Developmental Biology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Medizin
    Notizen: The number of H+ ejected during passage of 2e- through each energy-conserving site of the mitochondrial respiratory chain (the H+/site ratio) was measured in three ways. In each case transmembrane movements of endogenous phosphate were minimized. (1) Measurement of the uptake of weak acids during loading of mitochondria with Ca2+ demonstrated that 2.0 weak acid anions were accumulated per Ca2+ ion. Since 1.7 to 2.0 Ca2+ ions were taken up per site, these data correspond to an H+/site ratio of 3.5 to 4.0. (2) More direct measurement of H+ ejection using the oxygen pulse technique demonstrated that the H+/site ratio was 3.0. In these experiments phosphate movements were prevented by addition of N-ethylmaleimide to inhibit phosphate-hydroxide antiport, by washing the mitochondria to remove endogenous phosphate, or by working at 5°C to reduce the rate of phosphate transport. When phosphate movements were allowed, H+/site ratios of 2.0 were observed. (3) Measurement of the initial steady rates of oxygen consumption and H+ ejection following addition of substrate to aerobic, substrate-limited mitochondria yielded H+/site ratios of 2.0, which were elevated to 4.0 when phosphate transport was prevented as described above.Previous determinations of the H+/site ratio were thus underestimates due to the unrecognized movements of endogenous phosphate; our results show that the H+/site ratio is at least 3.0 and may be as high as 4.0.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jcp.1040890415
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  • 4
    Digitale Medien
    Digitale Medien
    Increased PRPP synthetase activity in cultured rat hepatoma cells containing mutations in the hypoxanthine-guanine phosphoribosyltransferase gene (1976)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 88 (1976), S. 331-342 
    Details
    ISSN: 0021-9541
    Schlagwort(e): Life and Medical Sciences ; Cell & Developmental Biology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Medizin
    Notizen: Nine independently derived clones of mutagenized rat hepatoma cells selected for resistance to 6-mercaptopurine (6-MP) or 6-thioguanine (6-ThioG) have been isolated. Each has severely reduced catalytic activity of hypoxanthine-guanine phosphoribosyltransferase (HPRT) and seven of them possess significantly increased activities of phosphoribosylpyrophosphate (PRPP) synthetase. The degrees of elevations of PRPP synthetase activities do not correlate with the degrees of deficiencies of HPRT activities.The cells from one of these clones, 1020/12, possess 40% of the normal HPRT catalytic activity and overproduce purines. We have extensively examined the cells from this clone. Immunotitration studies of 1020/12 cells indicate that there is a mutation in the structural gene for HPRT. Although they possess increased specific catalytic activities of the enzyme, PRPP synthetase, the catalytic parameters, heat stability, and isoelectric pH of PRPP synthetase from 1020/12 cells are indistinguishable from those of the enzyme from wild-type cells.The cause of purine overproduction by 1020/12 cells appears to be the elevated PRPP synthetase activity, rather than a PRPP “sparing” effect stemming from reduced HPRT activity. Support for this idea is provided by the observation that the complete loss of HPRT activity in a clone derived from 1020/12 cells does not further enhance the levels of PRPP synthetase or purine overproduction.We propose that the elevated levels of PRPP synthetase activity in these HPRT deficient cells result from a mutational event in the structural gene for HPRT, and that this causes the disruption of a previously undescribed regulatory function of this gene on the expression of the PRPP synthetase gene.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jcp.1040880309
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  • 5
    Digitale Medien
    Digitale Medien
    Abnormal regulation of de novo purine synthesis and purine salvage in a cultured mouse T-cell lymphoma mutant partially deficient in adenylosuccinate synthetase (1979)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 99 (1979), S. 139-151 
    Details
    ISSN: 0021-9541
    Schlagwort(e): Life and Medical Sciences ; Cell & Developmental Biology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Medizin
    Notizen: The isolation and characterization of a mutant murine T-cell lymphoma (S49) with altered purine metabolism is described. This mutant, AU-100, was isolated from a mutagenized populatio of S49 cells by virtue of its resistance to 0.1 mM 6-azauridine in semisolid agarose. The AU-100 cells are resistant to adenosine mediated cytotoxicity but are extraordinarily sensitive to killing by guanosine.High performance liquid chromatography of AU-100 cells extracts has demonstrated that intracellular levels of GTP, IMP, and GMP are all elevated about 3-fold over those levels found in wild type cells. The AU-100 cells also contain an elevated intracellular level of pyrophosphoribosylphosphate (PPriboseP), which as in wild type cells is diminished by incubation of AU-100 cells with adenosine. However AU-100 cells synthesize purines de novo at a rate less than 35% of that found in wild type cells.In other growth rate experiments, the AU-100 cell line was shown to be resistant to 6-thioguanine and 6-mercaptopurine. Levels of hypoxanthine-guanine phosphoribosyltransferase (HGPRTase) measured in AU-100 cell extracts, however, are 50-66% greater than those levels of HGPRTase found in wild type cell extracts. Nevertheless this mutant S49 cell line cannot efficiently incorporate labeled hypoxanthine into nucleotides since the salvage enzyme HGPRTase is inhibited in vivo.The AU-100 cell line was found to be 80% deficient in adenylosuccinate synthetase, but these cells are not auxotrophic for adenosine or other purines. The significant alterations in the control of purine de novo and salvage metabolism caused by the defect in adenylosuccinate synthetase are mediated by the resulting increased levels of guanosine necleotides.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jcp.1040990115
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