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911.
Induced release and metabolism of arachidonic acid from myeloid cells by purified colony-stimulating factor 总被引:1,自引:0,他引:1
V A Ziboh A M Miller M C Wu A A Yunis J Jimenez G Wong 《Journal of cellular physiology》1982,113(1):67-72
The in vitro incubation of cells from turpentine-induced rat myeloid hyperplastic marrow and peritoneal monocyte/macrophage with 14C-arachidonic acid resulted in the incorporation of the radiolabel into the particulate phospholipids. Challenge of the radiolabeled cells with a highly purified type I CSF (CSF I) from human pancreatic carcinoma cells in continuous culture resulted in the hydrolysis and release of the 14C-arachidonic acid from the cellular phospholipids. The simultaneous challenge of the prelabeled cells with CSF-I and its specific antibody (anti-CSF-I antibody) inhibited the CSF-I induced hydrolysis of 14C-arachidonic acid from the cells. These results confer a specificity on the CSF-I induced release of arachidonic acid from the cellular phospholipids. Our data also demonstrated that the 14C-arachidonic acid released from the cellular phospholipids was further transformed into products of the cyclooxygenation and lipoxygenation pathways by cellular enzyme systems in both populations of cells. Interestingly, our data also indicate that the challenge of the granulocytic hyperplastic marrow cells and the monocyte/macrophage cells with purified CSF-I resulted in a higher generation of lipoxygenase products in the predominantly granulocytic cell population than in the population rich in monocyte/macrophage cells. The biological significance of this observation remains to be further explored. Thus, the CSF-I induced release of cellular arachidonic acid explains, at least in part, the presence of prostaglandins and other metabolites of arachidonic acid that are found in the media of hemopoietic cells incubated with a variety of CSF preparations. 相似文献
912.
Mitotic gene conversion in the D7 strain of Saccharomyces cerevisiae was significantly enhanced by exposure to non-enzymatic browning reaction products. These products were formed during the heating of sugar (caramelization reaction) or sugar-amino acid mixtures (Maillard reaction) at temperatures normally used during the cooking of food. Several modulating factors of this convertogenic activity were identified. These factors included two main groups: (1) trace metals which are widely distributed in the environment; and (2) several cellular enzymatic systems. The convertogenic activities of a heated glucose-lysine mixture and a commercial caramel powder were completely suppresses when yeast were concurrently exposed to these products and to either FeIII or CuII. Equimolar concentrations of MnII or sodium selenite had no effect on the convertogenic activity of the products of either model system. Horse-radish peroxidase, beef liver catalase and rat liver S9 preparations each decreased the frequency of gene conversion induced by the caramel powder and the heated glucose-lysine products. This modulating activity of the enzymes was lost if they were heat-inactivated. These studies indicate the presence of a variety of protective mechanisms which can modify genotoxic components in complex food mixtures. 相似文献
913.
Do benzodiazepines bind at adenosine uptake sites in CNS? 总被引:6,自引:0,他引:6
Benzodiazepines inhibit adenosine uptake into rat cerebral cortical synaptosomes and their potency as inhibitors of adenosine uptake is closely correlated with therapeutic efficacy. Agents which possess “benzodiazepine like” activities such as CL218,872, zopiclone and fominoben and which displace benzodiazepine binding to brain cell membranes, are also inhibitors of adenosine uptake into brain synaptosomes. The IC50 values of all these compounds as inhibitors of adenosine uptake are in close agreement with the IC50 values obtained for the displacement of benzodiazepine binding to the brain receptors. Adenosine uptake inhibitors (dipyridamole, hexobendine, papaverine, 6-(2-hydroxy-5-nitrobenzyl)thioguanosine) which competitively inhibit adenosine uptake, presumably by blocking adenosine binding to its carrier-protein, are competitive inhibitors of diazepam binding to the brain membrane receptors. The finding of a pronounced correlation between inhibition of benzodiazepine binding and inhibition of adenosine uptake further supports the proposal that benzodiazepines may exert part of their pharmacological action through the inhibition of adenosine uptake. 相似文献
914.
915.
Evidence for the Presence of CDP-Ethanolamine: 1,2-diacyl-sn-glycerol Ethanolaminephosphotransferase in Rat Central Nervous System Myelin 总被引:3,自引:3,他引:0
Highly purified rat brain myelin isolated by two different procedures showed appreciable activity for CDP-ethanolamine: 1,2-diacyl-sn-glycerol ethanolaminephosphotransferase (EC 2.7.8.1). Specific activity was close to that of total homogenate and approximately 12-16% that of brain microsomes. Three other lipid-synthesizing enzymes, cerebroside sulfotransferase, lactosylceramide sialyltransferase, and serine phospholipid exchange enzyme, were found to have less than 0.5% the specific activity in myelin compared with microsomes. Washing the myelin with buffered salt or taurocholate did not remove the phosphotransferase, but activity was lost from both myelin and microsomes by treatment with Triton X-100. It resembled the microsomal enzyme in having a pH optimum of 8.5 and a requirement for Mn2+ and detergent, but differed in showing no enhancement with EGTA. The diolein Km was similar for the two membranes (2.5-4 x 10(-4) M), but the CDP-ethanolamine Km was lower for myelin (3-4 x 10(-5) M) than for microsomes (11 - 13 x 10(-5 M). Evidence is reviewed that this enzyme is able to utilize substrate from the axon in situ. 相似文献
916.
Gangliosides were compared with glycoproteins as potential receptors for Sendai virus by incorporating measured amounts of the glycoconjugates into lecithin-cholesterol liposomes and measuring binding by a hemagglutination assay with sheep erythrocytes. HeLa cell gangliosides showed no binding activity toward the virus up to 15 micrograms of sialic acid per 5 mumol of lecithin-cholesterol, whereas HeLa cell glycoproteins incorporated into similar liposomes caused avid virus binding below 1 microgram of sialic acid. These sialoglycoproteins could be separated from the bulk of cell proteins by multiple chloroform-methanol extractions. Purified rat brain gangliosides at a level of 120 micrograms of sialic acid in liposomes did not bind virus, whereas chloroform-methanol-extracted rat brain proteins caused only marginal binding. Bovine brain gangliosides differed slightly from the rat brain mixture in showing weak binding properties. Our results thus indicate that glycoproteins, rather than gangliosides, are the natural receptors for Sendai virus and that tissues differ as to the quantity of such protein receptors. 相似文献
917.
918.
Ordered conformation of polypeptides and proteins in acidic dodecyl sulfate solution 总被引:17,自引:0,他引:17
The conformation of some polypeptides and proteins in sodium dodecyl sulfate (NaDodSO4) solutions was studied by circular dichroism. The type and extent of induced structure depend on their helix- and beta-forming potential. Anionic side groups in segments of helix or beta form tend to destabilize the ordered structure unless they are protonated. beta-Endorphin has one Glu inside a predicted helical segment; its helicity in a NaDodSO4 solution is enhanced at pH below 4. alpha-Melanocyte-stimulating hormone having a Glu in a beta segment undergoes a pH-induced coil to beta transition in 1.25 mM NaDodSO4 (excess surfactant will disrupt the beta form). Reduced somatostatin assumes a beta form in 2 mM NaDodSO4 and a partial helix in 25 mM NaDodSO4, both of which are unchanged in acidic pH because it lacks -COOH groups. The unordered gastrin with five consecutive Glu's becomes helical in a NaDodSO4 solution at pH 4. Neurotensin with one Glu has no structure-forming potential and is unordered in both neutral and acidic NaDodSO4 solutions. This charge effect also manifests in segments of ordered structure for polypeptides and proteins such as glucagon, cytochrome c, parvalbumin, ribonuclease A, and lysozyme. The effect is especially predominant in tropomyosin that is rich in clusters of anionic side groups. Its more than 90% helicity is reduced to about one-half in a neutral NaDodSO4 solution, but most of it can be restored by lowering the pH to 2.4. 相似文献
919.
A new method is described for the immobilization of enzymes and other proteins onto hydrophobic gels. Trypsin, for example, can be quantitatively immobilized by reaction with sodium cyanoborohydride and dodecyladehyde-coated Octyl-Sepharose. Noncovalent interactions between the hydrophobic gel and approximately 10 resulting dodecylamino groups in the modified enzyme bind it very strongly but do not affect its ability to hydrolyze benzolarginine ethyl ester. The same procedure can also be used to immobilize E. Coli asparaginase and yeast alcohol dehydrogenase in high yield. 相似文献
920.