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  • 1990-1994  (3)
  • 1970-1974  (10)
  • 1
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: : “Flooding” amino acid pools with high doses of labeled amino acids of low specific activity has been proposed to minimize the effects of recycling of amino acids derived from protein degradation on the specific activity of the amino acid precursor pool for protein synthesis. We have examined the influence of recycling on the precursor pool for protein synthesis under conditions in which plasma valine concentrations were normal (0.19 mM) and “flooded” (10-28 mM) by comparing the steady-state specific activity of the tRNA-bound valine with that of the plasma valine. Under normal and “flooding” conditions, the relative contributions of valine from protein degradation to the precursor pool were 63 and 26%, respectively; “flooding” with a plasma level of 28 mM raised the brain acid-soluble pool level to 3.1 mM but was no more effective in decreasing the relative contribution of valine from protein degradation to the precursor pool than “flooding” with a plasma level of 17 mM valine, which raised the brain acid-soluble level only to 2.3 mM. The results of these studies show that “flooding” amino acid pools does indeed reduce the effect of recycling on the precursor amino acid pool for protein synthesis, but it does not totally eliminate it.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The quantitative autoradiographic L-[1–14C]leucine method for the determination of regional rates of cerebral protein synthesis in vivo takes into account recycling of unlabeled leucine derived from protein degradation into the precursor pool for protein synthesis. We have evaluated the degree of recycling by measuring the ratio of the apparent steady-state leucine specific activity in the precursor amino acid pool (tRNA-bound leucine) to that in the arterial plasma. In the whole brain of the conscious rat this ratio (λWB) equals 0.58. The equivalent ratio for leucine in the acid-soluble pool in whole brain (ΨWB) is 0.49. A first-degree polynomial equation for λWB as a function of ΨWB was fitted from paired determinations. To determine the degree of recycling in local regions of the brain, we have measured in individual brain regions (i) Ψi and calculated λi assuming that the fitted equation also applies to these localized regions. Our results indicate that the degree of recycling into the precursor pool does vary regionally; λi in the individual regions varies from 0.62 in the hypoglossal nucleus to 0.50 in the globus pallidus. Local rates of protein synthesis were then determined by the autoradiographic technique with regional corrections for recycling of unlabeled leucine. Rates of leucine incorporation into protein averaged 6.1 nmol/g of tissue/min in the brain as a whole, with the rates in gray matter about twice those in white matter.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 22 (1974), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract— Chronic ethanol ingestion in rats leads to a slow rise in brain alcohol dehydrogenase activity which levels off after 2 weeks at approximately twice the initial activity. The half-time of the rise is approximately 8 days. Abrupt withdrawal of the ethanol is followed by a rapid decline of the brain alcohol dehydrogenase activity to the normal level with a half-time of approximately 15 h. The difference in time constants between the rise in enzyme activity during ethanol-feeding and its decline following withdrawal suggests that the increased enzyme activity is at least in part the result of a reduced rate constant of enzyme degradation in the presence of ethanol. The effect of ethanol on brain alcohol dehydrogenase activity is not altered by supplementation of the diet with carbohydrate or vitamins. The effect is seen only in the cerebral hemispheres and not in the brain-stem. Acquisition of tolerance to ethanol during chronic ethanol ingestion and its extinction following withdrawal follow almost the same time courses as the changes in brain alcohol dehydrogenase activity.
    Type of Medium: Electronic Resource
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  • 4
    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: Abstract— Blood flow was measured quantitatively in 35 structures of the brains of dogs of various ages from birth to maturity. In general, values were low at birth and rose to maximal levels between 3 and 7 weeks of postnatal age; declines from the peak levels then followed until values characteristic of maturity were attained by 13 weeks of postnatal age. From relatively uniform perfusion rates throughout the brain at birth there gradually emerged a marked heterogeneity, in parallel with the structural and functional maturation and differentiation known to occur in the brain during this period of life. Our observations may reflect the summation of the changes in energy demands associated on the one hand with biosynthetic processes essential for growth and development and with the support for progressively increasing functional activities on the other.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 22 (1974), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 21 (1973), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract— Microsomes from rat brain exhibited protein kinase activity which was stimulated by cyclic AMP when assayed in the presence of exogenous protein substrate, such as thymus histone. In the absence of exogenous substrate some phosphorylation of microsomal protein occurred, but no stimulation by cyclic AMP could be discerned, probably because of limitations of substrate. The maximal activity of microsomal protein kinase observed in the presence of saturating concentrations of histone and the optimal concentration (5 μm) of cyclic AMP remained essentially unchanged from birth to early adulthood, but the magnitude of the stimulation by cyclic AMP was significantly higher at birth than at 30 days of age. Brain ribosomal proteins could be phosphorylated by the cyclic AMP-dependent brain protein kinase. Their total capacity for acceptance of phosphate by means of this phosphorylation reaction remained unchanged throughout the postnatal development of the brain. Our results are consistent with the possibility that phosphorylation of ribosomal protein mediated by cyclic AMP-dependent protein kinase may play a a role in the postnatal regulation of cerebral protein synthesis, as a result of the changes in the levels of cyclic AMP known to occur in brain during postnatal maturation.
    Type of Medium: Electronic Resource
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  • 7
    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: Abstract— The enzymes catalysing ethanol metabolism, alcohol dehydrogenase (EC 1.l.1.1) and aldehyde dehydrogenase (EC 1.2.1.3), were assayed in a variety of neural and somatic tissues of the rat, the human counterparts of which are known to be vulnerable to excessive ethanol. The activity of alcohol dehydrogenase was assayed by the coupled oxidation of ethanol and reduction of lactaldehyde, a method which we have recently found to be sufficiently sensitive and specific to measure the relatively low levels of activity in whole brain. Detectable activities of these enzymes were found in peripheral nerve, skeletal muscle, retina, optic nerve and various regions of brain, as well as in a variety of non-neural tissues. The levels of the enzymic activities in all tissues were markedly lower than those of liver, but probably sufficient to perform a local function in the metabolism of ethanol or other endogenous substrates. The activity of alcohol dehydrogenase in the various tissues, like that of liver, was confined to the cytosol and exhibited kinetic properties and responses to inhibitors almost identical to those of the liver enzyme. We consider the results to be consistent with the hypothesis that the pathological effects of alcohol may be related, at least in part, to local mechanisms for the metabolism of alcohol.
    Type of Medium: Electronic Resource
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  • 8
    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: Abstract— The continuous exposure of newborn rats to 70–80 per cent oxygen at atmospheric pressure throughout the iirst 9 days of life significantly inhibited the growth of the brain which normally occurs during this period of life. The accumulations of DNA, RNA, total protein, and proteolipid protein which accompany brain growth during this period were all approximately proportionately depressed by the oxygen-enriched atmosphere. RNA/DNA and protein/DNA ratios were unaffected. The increase in brain mass in the first week of life reflects mainly cell proliferation, and since the decreased DNA accumulation occurred with no changes in RNA/DNA and protein/DNA ratios, we conclude that the effect of oxygen was to inhibit cellular division. We estimate that the oxygen exposure caused an approximately 7 per cent deficit in the cell population of the brain. These results indicate that the use of elevated concentrations of oxygen may have serious deleterious effects on the growth and development of the brain.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 17 (1970), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract— A significant level of alcohol dehydrogenase activity has been demonstrated in the soluble fraction of rat brain. The pH optimum, kinetic properties and response to inhibitors are similar to those of liver alcohol dehydrogenase. The nutritional state of the animal, such as that associated with feeding or fasting, appeared to have no effect on the levels of the alcohol dehydrogenase activities in either liver or brain. A cerebral mechanism for the metabolism of ethanol may be involved in local biochemical adjustments in tissues during exposure to alcohol and may play a significant role in the pathogenesis of the neural disorders which can accompany chronic alcohol ingestion or acute withdrawal.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract— The activity of d(-)-β-hydroxybutyrate dehydrogenase, a mitochondrial enzyme involved in ketone body metabolism, was found to be low in rat brain at birth, to rise. progressively to a peak during the first 3 weeks of postnatal life, and to decline after weaning to the low levels characteristic of the mature brain. Hyperthyroidism, induced from birth by administration of exogenous thyroxine, accelerated the postnatal development of the enzymic activity in brain and shifted the entire pattern of maturation to approximately 2 days earlier. The effects on the activity of the enzyme were the same with excessive doses of thyroxine which exaggerated the catabolic effects of the hormone and retarded brain and body growth or with lesser doses which had no apparent effects on brain and body growth or on the contents of nucleic acids and proteins in the brain. The accumulation of proteolipid protein in brain was also enhanced in hyperthyroidism. These results suggest that biochemical maturation of the brain is accelerated in hyperthyroidism.
    Type of Medium: Electronic Resource
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