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  • 1
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 67 (1996), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Phospholipase D activity of rat brain neuronal nuclei, measured with exogenous phosphatidylcholine as substrate, was characterized. The measured activity of neuronal nuclei was at least 36-fold greater than the activity in glia nuclei. The pH optimum was 6.5, and unsaturated but not saturated fatty acids stimulated the enzyme. The optimal concentration of sodium oleate for stimulation of the enzyme activity was 1.2 mM in the presence of 0.75 mM phosphatidylcholine. This phospholipase D activity was cation independent. In the absence of NaF, used as a phosphatidic acid phosphatase inhibitor, the principal product was diglyceride; whereas in the presence of NaF, the principal product was phosphatidic acid. The phospholipase D, in addition to having hydrolytic activity, was able to catalyze a transphosphatidylation reaction. Maximum phosphatidylethanol formation was seen with 0.2–0.3 M ethanol. GTPγS, ATPγS, BeF2, AIF3, phosphatidic acid, and phosphatidylethanol inhibited the neuronal nuclei phospholipase D activity. The addition of the cytosolic fraction of brain, liver, kidney, spleen, and heart to the incubation mixtures resulted in inhibition of the phospholipase D activity. Phospholipase D activity was detectable in nuclei prepared from rat kidney, spleen, heart, and liver.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 45 (1985), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The phospholipase D of the rat brain synaptic membrane possesses the highest activity of this enzyme of any mammalian tissue examined. The synaptic phospholipase D activity is latent and barely detectable in the absence of 4 mM sodium oleate. Several other fatty acids were either less effective or ineffective as stimulators of activity compared to this monounsaturated fatty acid. The activity was decreased by hemicholinium-3, an inhibitor of choline uptake and slightly activated by neostigmine, an acetylcholinesterase inhibitor. Incubation of synaptosomes in the presence of sodium oleate and acetyl-coenzyme A resulted in the formation of a product chromatographing with acetylcholine. Acetylcholine formation was nearly undetectable in the absence of sodium oleate or acetyl-coenzyme A. These results implicate synaptosomal phospholipase D in releasing choline from phosphatidylcholine for acetylcholine formation.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 42 (1984), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Rat brain microsomes were preincubated with S-adenosylmethionine (SAM), MgCl2, and CaCl2, then re-isolated, and the activity of Na+,K+-ATPase determined. SAM inhibited the Na+,K+-ATPase activity compared with microsomes subjected to similar treatment in the absence of SAM. A biphasic inhibitory effect was observed with a 50% decrease at a SAM concentration range of 0.4 μM-3.2 μM and a 70% reduction at a concentration range above 100 μM. Inclusion of either S-adenosylhomocysteine or 3-deazaadenosine in the preincubations prevented the SAM inhibition of Na+,K+-ATPase activity. The inhibition by SAM appeared to be Mg2+- or Ca2+-dependent.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 39 (1982), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The hydrolytic and transphosphatidylation activities of rat brain microsomal phospholipase D were highly latent in the absence of an appropriate activator. The most suitable surfactants for this activation were oleate and palmitoleate. Besides the bile acids and unsaturated fatty acids, other naturally occurring surfactants, such as lysophospholipids, acidic phospholipids, acyl-CoA's, and gangliosides, were inactive. Taurodeoxycholate, at optimal concentration, produced a profound inhibition of oleate activation. Phospholipase D activity was detectable in all rat tissues investigated. The optimal incubation temperature for phospholipase D was 30°C, with a break point at 16.1°C in an Arrhenius plot.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 60 (1993), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The biosynthesis of phosphatidylserine in mammalian tissues is catalyzed by the serine base exchange enzyme. The activity of this membrane-bound enzyme can be manipulated by amphiphiles. Amphiphilic cations, such as oleylamine, W-7, chlorpromazine, and didodecyldimethylamine, stimulate the serine base exchange activity. Amphiphilic anions, such as bis(2-ethylhexyl) hydrogen phosphate and cholesterol sulfate, inhibit the serine base exchange activity. These effects are more pronounced at pH 7.0 than at the pH optimum of 8.5 for this enzyme. Both the stimulators and the inhibitors alter the Vmax values without changing the Km value for serine, suggesting that their mechanism of action is related to interactions of the membrane-bound cosubstrate, phosphatidylethanolamine, with the membrane-bound enzyme. The optimal concentration of stimulator varies with the amount of membrane protein present; however, supraoptimal concentrations cause inhibitions. It is proposed that the amphiphilic cations enhance the interaction of the phosphorylethanolamine moiety of the membrane-bound cosubstrate with the enzyme and the amphiphilic anions interfere with such an interaction. Some of the pharmacological properties of these amphiphilic cations, employed clinically as antidepressants, may be mediated by modulation of the serine base exchange enzyme activity.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 48 (1987), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Phosphatidylethanol (Peth) formation catalyzed by the transphosphatidylation activity of phospholipase D was demonstrated to occur in a rat brain synaptosomal enriched preparation. The optimal pH was determined to be 6.5, and the optimal ethanol concentration was determined to be 0.3–0.4 M with an apparent Km of 0.2 M. Peth formation was barely detectable in the absence of an appropriate activator and several unsaturated fatty acids were found to be effective activators. The concentrations of oleic acid required for maximum activation varied with the concentration of exogenous phosphatidylcholine present in the incubation mixtures. All detergents tested were significantly less active than the unsaturated fatty acids and divalent ions were not required for Peth formation. Phosphatidylcholine was the most effective phosphatidyl donor of the phospho-lipids tested. Peth forming activity was greatest in the synap-tic membrane fraction of the various brain subfractions examined. The 12,000 g-100,000 g paniculate fraction of lung, heart, and adipose tissue had activities similar to that of brain.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 46 (1986), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The effect of the presence of nitrogenous bases in the growth medium of fetal rat brain aggregating cell cultures was investigated. The presence of either N-dimethylethanolamine (MME) or N,N-dimethylethanolamine (DME) in the growth medium resulted in significant increase of the corresponding phospholipid, phosphatidyl-N-monomethylethanolamine (PMME) or phosphatidyl-N,N-dimethylethanolamine (PDME). They represented 28% and 32% of the total phospholipids, respectively. The presence of the new phospholipids was accompanied by a significant decrease of phosphatidyl ethanolamine (PE) and phosphatidylcholine (PC). Cells grown in the presence of ethanolamine or choline had only barely detectable amounts of PMME and PDME. Intact cells previously grown with the bases were incubated with [methyl-3H]methionine. Incubation of cells previously grown in presence of the bases MME and DME resulted in a marked increase of radioactivity in the corresponding phospholipids possessing one additional methyl group, PDME and PC respectively. The incorporation of S-adenosyl[methyl−3H]methionine (AdoMet) was examined in cell homogenates incubated in presence or absence of either PMME or PDME acceptors. The addition of these exogenous phospholipids caused a three or fourfold stimulation of radioactivity incorporated into the total phospholipids of cells grown in the absence of nitrogen bases. The cells grown in presence of either MME or DME in the culture medium did not show an increased incorporation of methyl groups from AdoMet into the total phospholipids after addition of exogenous acceptors. This work suggests that MME and DME incorporated into the corresponding phospholipids function as effective substrates for phospholipid-N-methylation.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Rat CNS myelinated axons were fractionated by sucrose density gradient centrifugation with a zonal rotor. Fraction VI, obtained at 28–30% sucrose, appeared, on the basis of the presence of related marker enzymes, to be enriched in axolemma. Phospholipid-N-methyltransferases (PMTs) and base-exchange enzymes were associated with fraction VI. PMT activity was significantly stimulated by the addition of either phosphatidylmonomethylethanolamine or phosphatidyldimethylethanolamine but the PMT activity of the homogenate or the myelinated axons was unresponsive. Recoveries of the ethanolamine, serine, and choline base-exchange activities were 14.4%, 13.8%, and 3.4%, respectively, of that present in the myelinated axons. The myelin-rich fraction obtained simultaneously seems contaminated with other membrane fractions.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 40 (1983), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: An axolemma-enriched fraction prepared from a purified myelinated axon fraction isolated from rat CNS was found to contain phospholipase D at a specific activity similar to that of a microsomal fraction isolated from whole brain. There was a concomitant threefold enrichment in the specific activity of phospholipase D and acetylcholinesterase in the axolemma-enriched fraction compared with the specific activities of these enzymes in the starting white matter whole homogenate. This axonal phospholipase D may be involved in remodeling of phospholipid, which in turn may affect axonal functions such as ion translocation.
    Type of Medium: Electronic Resource
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