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  • 1
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: A Sialoglycopeptide from bovine cerebral cortex cells was purified to apparent homogeneity by a procedure that included chloroform/methanol extraction, diethylaminoethyl ion exchange chromatography, wheat germ agglutinin affinity chromatography, size-exclusion HPLC, and hydrophobic interaction chromatography. The cell surface inhibitor had a molecular weight of ∼18,000, no subunit composition was detectable on reduction and polyacrylamide gel electrophoresis analysis, and the glycopeptide apparently contained sialic acid, as illustrated by its ability to bind to Limulus polyhemus lectin. Deglycosylation of the molecule, however, did not reduce its protein synthesis inhibitory activity. As little as 20 ng of the Sialoglycopeptide was capable of inhibiting protein synthesis in a wide variety of fibroblast cell lines but not in transformed cells. Mice immunized with the Sialoglycopeptide produced antibodies that, when bound to protein A-agarose gel, removed the inhibitory activity from solution. The antibodies were used to identify a single isoelectric focused band and to establish the pI of 3.0 for the molecule.
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 27 (1976), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract– The addition of a dialyzed cytosol preparation from various types of mouse tissue, guinea-pig brain, and neuroblastoma cells resulted in an increased incorporation of [3H]GTP into RNA by mouse brain nuclei. In addition to a stimulation of the incorporation of [3H]GTP into RNA. the presence of these cytosol preparations also caused a significant increase in nuclear RNA transcript size. Although all cell cytosols appeared to influence nuclear RNA metabolism to some degree, dialyzed mouse serum had little stimulatory effect on brain nuclear RNA synthesis and failed to cause an increase in RNA product size. The polyanion, heparin, was found to be highly stimulatory to brain nuclear RNA synthesis although the size of the resulting RNA products was not significantly altered. RNA synthesis by neuronal and glial nuclei, isolated from adult brain tissue, showed a differential response to the presence of brain cytosol preparations. In the absence of cytosol, RNA synthesis by neuronal nuclei was more active than that measured in glial nuclei, and when the RNA products were analyzed by sucrose gradient centrifugation, those of glial nuclei were considerably larger than those isolated from neuronal nuclei. The addition of cytosol caused a significant increase in RNA transcript size with neuronal nuclei of adult brain tissue while little, if any, change in the size of the RNA products was measured with nuclei isolated from glial cells. Although an overall increase in product size could be measured in response to the addition of dialyzed cytosol with neuronal nuclei of 2,10, 20-day old and adult (over 60 days of age) brain tissue, a greater response was measured with nuclei prepared from the brains of more mature animals where the proportion of larger RNA products (〉10S) was greatly increased.
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 18 (1971), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract— Ribosomes, isolated from brain tissue of mice of various ages, were tested for their ability to participate in cell-free protein synthesis and to bind polyuridylic acid. Although protein synthesis was markedly reduced by ribosomal preparations obtained from increasingly older animals, no significant differences could be measured with respect to template RNA binding. Similar binding properties were also measured with ribosomal subunits purified from young and mature brain cell ribonucleoprotein particles. In addition, no differences could be detected in the relative firmness of template RNA binding that could explain the maturation-dependent loss in ribosomal activity.
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 16 (1969), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract— Aminoacyl-RNA synthetase activity in mouse brain tissue was measured during the first few days after birth. Although the rate of protein synthesis rapidly diminished during this period, the activity of these specific enzymes was not reduced. In contrast, the binding of tyrosine and arginine was actually greater when the older enzyme preparations were employed. The ability of tRNA to bind amino acids during this critical stage of development was tested. Preparations of tRNA, isolated from 2-, 7-, 11- and 13-day-old, and adult brain tissue were employed with both young and old enzymes. No significant loss in binding activity was measured with these tRNA preparations.
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 26 (1976), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Incubation of brain cell suspensions with 14 mM-phenylalanine resulted in rapid alterations of amino acid metabolism and protein synthesis. Both thc rate of uptake and the final intracellular concentration of several radioactively-labelled amino acids were decreased by high concentrations oi phenylalanine. By prelabelling cells with radioactive amino acids, phenylalanine was also shown to effect a rapid loss of the labelled amino acids from brain cells. Amino acid analysis after the incubation of the cells with phenylalanine indicated that several amino acids were decreased in their intracellular concentrations with effects similar to those measured with radioisotopic experiments (large neutral 〉 small and large basic 〉 small neutral 〉 acidic amino acids). Although amino acid uptake and efflux were altered by the presence of 14 mwphenylalanine, little or no alteration was detected in the resulting specific activity of the intracellular amino acids. High levels of phenylalanine did not significantly altcr cellular catabolism of either alanine, lysine, leucine or isoleucine. As determined by the isolation of labcllcd aminoacyl-tRNA from cells incubated with and without phenylalanine, there was little or no alteration in the level of this precursor for radioactive alanine and lysine. There was, however, a detectable decrease in thc labelling of aminoacyl-tRNA for leucine and isoleucine. Only aftcr correcting for the changes of the specific activity of the precursors and thcir availability to translational events, could the effects of phenylalanine on protein synthesis be established. An inhibition of the incorporation into protein for each amino acid was approximately 20%.
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 23 (1974), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: —The elucidation of the translational regulatory events which function during the critical fetal and neonatal period is an important prerequisite to our understanding of normal, as well as abnormal, brain growth and differentiation. Brain cell suspensions and cell-free homogenates were employed to study the protein synthetic activity during the maturation of fetal- neural tissue. The results clearly demonstrated that while neural tissue from 1-day postnatal mice was 10 times more active in protein synthesis than brain tissue from adult mice, the former was many fold less active in translational events than fetal neural tissue from 13-day post-zygotic mice. Fetal polypeptide synthetic activity was found to decrease from the 13th day to the 19th day post-zygotic. This decrement in the translational activity was not due to amino acid availability or pools, or to differences, quantitatively or qualitatively, in polysome concentrations. The enhanced rate of protein synthetic activity measured with neural tissue from 13-day post-zygotic mice was shown to be due to an increase in rate of protein synthesis and not to an enhanced rate of protein degradation.
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 23 (1974), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract— The activity and kinetic characteristics of tRNA methyltransferases were measured with enzyme preparations obtained from neonatal and adult mouse brain tissue. Both neonatal and mature brain enzyme preparations were shown to contain a considerable amount of protein methylase activity which could interfere with the measurement of the tRNA methyltransferases. When increasing amounts of the unfractionated enzymes from young and adult neural tissue were added to reaction mixtures, the saturation kinetics were found to be considerably different. However, fractionation of the samples by precipitation at pH 5 resulted in an increase in the enzyme activity of preparations obtained from adult brain. Although the precipitation at pH 5 allowed a quantitative recovery of the enzyme activity of immature brain samples, this partial purification step led to an apparent activation of the tRNA methyltransferases in adult preparations. This activation was shown to be independent of differential changes in the thermolability of the enzymes but rather to be associated with an increase in the sites methylated and the measured affinity of the adult enzyme preparations with the tRNA substrate. Nicotinamide, a potent inhibitor of tRNA methyltransferase activity in other tissues, was shown to be ineffective in modulating brain tRNA methyltransferase activity. The results are discussed in light of the possible modulation of the activity of specific enzyme species and the alterations in the synthesis of nucleic acid precursors during neural development.
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 20 (1973), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract— The level of tRNA in mouse brain tissue was measured at various stages of postnatal development. The amount of tRNA per unit of brain wet weight was little, if at all, altered during the first 22 days after birth and decreased by 26 and 32 per cent by 56 days and maturity, respectively. On a DNA or cellular basis, there was no maturation-dependent decrease in tRNA content. The total amino acid acceptor activity of tRNA for seven different amino acids was measured during neural development. There were considerable differences in the tRNA acceptor activities of individual amino acids within an age group; however on a DNA basis, there was little difference between tRNA preparations obtained from newborn and adult mouse brain tissue. The in vivo levels of aminoacylated-tRNA for the seven amino acids of interest, were measured in brain tissue of 1–, 9–, 34, 70–day-old and adult (over 9 months old) mice. Alterations in tRNA level, total tRNA acceptor activity, for each amino acid, and the levels of in uivo aminoacylation of tRNA were shown to be independent of developmental alterations in brain amino acid pool sizes. The results are discussed with regard to the availability of cellular amino acids for translational events during early mammalian brain development.
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 19 (1972), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: —The regulation of protein synthesis by ribosomes isolated from mouse brain tissue was studied using a cell-free polyphenylalanine synthesizing system. Polypeptide synthesis was followed by assaying translocation and analysing the reaction products by BD-cellulose chromatography. The brain ribosomal activity could be divided by these methods into two distinct steps : binding of aminoacyl-tRNA to the ribosome and active translocation leading to subsequent polyphenylalanine synthesis. In comparison to initial binding of aminoacyl-tRNA, translocation in the cell-free system increased the incorporation of labelled phenylalanine by 10-fold. An analysis of the reaction products clearly showed active ribosomal synthesis of oligophenylalanine from [3H]phe-tRNA. Ribosomes isolated from neonatal brain tissue were 2–4 times as active as those obtained from adult brain tissue in polypeptide synthesis. In addition, polypeptides synthesized on the more active ribosomes from neonates tended to be of greater chain length than those from adult. Therefore, the maturation-dependent decrease in ribosomal protein synthetic activity during neural development was shown to be directly associated with the ribosome particles.
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 18 (1971), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The ability of brain ribosomes, isolated from mice of various ages, to bind phenylalanyl-tRNA was measured under various reaction conditions. In the presence of template RNA (polyuridylic acid) the binding could be measured by both enzymic and non-enzymic assays. In general, the binding requirements for the brain system were similar to those previously described for microbial and eukaryotic systems. Although previous studies have shown that ribosomes obtained from increasingly older mow brain tissue were less active in polyphenylalanine synthesis, no significant differences in phenylalanyl-tRNA binding to polysome complexes could be detected. The binding of phenylalanyl-tRNA by ribosomes isolated from both neonatal and mature mouse brain tissue was similar with regard to GTP and polyuridylic acid dependence, magnesium ion concentration and reaction kinetics. Similar binding of phenylalanyl-tRNA by young and mature brain ribosomes was also measured with ribonucleoprotein particles previously stripped with puromycin. The results are discussed in light of the rapid alteration of macromolecular synthesis during postnatal brain development and the possible role of the interaction between ribosomes and tRNA.
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