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1.
Free and polymerized tubulin in cultured bone cells and Chinese hamster ovary cells: the influence of cold and hormones 总被引:1,自引:1,他引:0
A low pH method of liposome-membrane fusion (Schneider et al., 1980, Proc. Natl. Acad. Sci. U. S. A. 77:442) was used to enrich the mitochondrial inner membrane lipid bilayer 30-700% with exogenous phospholipid and cholesterol. By varying the phospholipid-to- cholesterol ratio of the liposomes it was possible to incorporate specific amounts of cholesterol (up to 44 mol %) into the inner membrane bilayer in a controlled fashion. The membrane surface area increased proportionally to the increase in total membrane bilayer lipid. Inner membrane enriched with phospholipid only, or with phospholipid plus cholesterol up to 20 mol %, showed randomly distributed intramembrane particles (integral proteins) in the membrane plane, and the average distance between intramembrane particles increased proportionally to the amount of newly incorporated lipid. Membranes containing between 20 and 27 mol % cholesterol exhibited small clusters of intramembrane particles while cholesterol contents above 27 mol % resulted in larger aggregations of intramembrane particles. In phospholipid-enriched membranes with randomly dispersed intramembrane particles, electron transfer activities from NADH- and succinate-dehydrogenase to cytochrome c decreased proportionally to the increase in distance between the particles. In contrast, these electron- transfer activities increased with decreasing distances between intramembrane particles brought about by cholesterol incorporation. These results indicate that (a) catalytically interacting redox components in the mitochondrial inner membrane such as the dehydrogenase complexes, ubiquinone, and heme proteins are independent, laterally diffusible components; (b) the average distance between these redox components is effected by the available surface area of the membrane lipid bilayer; and (c) the distance over which redox components diffuse before collision and electron transfer mediates the rate of such transfer. 相似文献
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Dipl. Landw. Wilhelm Hartmann Dr. Kurt Zschau 《Archives Of Phytopathology And Plant Protection》2013,46(6):523-538
In den Jahren 1987 bis 1989 wurden die Auswirkungen und Effekte eines kombinierten Befalls des Winterweizens mit Sitobion avenae (Fabr.) und Puccinia recondita Rob.ex Desm. f.sp.tritici Erikss. untersucht. Dabei wurde das Verhalten der Schaderregerpopulationen und die Einflußnahme auf das Ertragsgeschehen bei separatem und simultanem Befall erfaßt. Während bei starkem Befall der oberen Blattetagen mit P.recondita eine Förderung der Aphidenpopulation an den Ähren der befallenen Pflanzen registriert werden konnte, war bei schwachem Braunrostbefall keine Einflußnahme auf die Blattläuse nachweisbar. Durch das kombinierte Auftreten beider Schaderreger kann es zu Reduktionen bei der Kornmasse/Ähre und bei der Tausendkornmasse kommen, die größer sind, als die Summe der Verluste bei Einzelbefall. Ähren stark braunrostbefallener Winterweizenpflanzen wurden zeitiger von S.avenae angeflogen und schneller besiedelt als diese von gesunden Kontrollpflanzen. Als Ursache für die Förderung der Populationsentwicklung von S.avenae werden durch P.recondita induzierte Veränderungen im Angebot an freien Aminosäuren in der Wirtspflanze diskutiert. 相似文献
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With the help of a ribonucleoprotein it is possible to precipitate collagen in a layer of fibers with a 700 Å period. As collagen is a constituent of many membrane systems in the body, it seemed interesting to investigate the permeability of ions and water through a native collagen membrane.The experiments were carried out with the help of an acryl glass apparatus, where an osmotic pressure, a hydrostatic pressure difference or both can be maintained between the two bulk phases separated by the membrane. The diffusion coefficients for NaCl and KCl were found to be comparable with those in other biological membranes (Ds = 9 · 10−7cm2 · s−1) whereas there is difference of more than three orders of magnitude in the hydraulic permeability (Lp = 6 cm4 · J−1 · s−1).Volume flow measurements caused by an osmotic gradient indicated that the reflection coefficient for NaCl and KCl is very small. In hydrostatic pressure experiments, the membrane shows a preferred direction for volume flows which seems to have something to do with the mode of preparation of the membrane. 相似文献
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M Str?ssle G Stark M Wilhelm 《International journal of radiation biology and related studies in physics, chemistry, and medicine》1987,51(2):287-302
Planar lipid membranes in the presence of the ion carriers valinomycin or nonactin were irradiated with 14 MeV electrons from a linear accelerator. A large increase of the membrane conductance by up to more than two orders of magnitude was found. The effect is virtually abolished either at high pH, or in the absence of oxygen, or in the presence of the radical scavenger ethanol. A further prerequisite for the effect is the presence of unsaturated fatty acid residues. A kinetic analysis of the carrier transport model based on current-voltage curves and on voltage-jump relaxation experiments was performed as a function of radiation dose. Only the translocation rate constant, kMS, of the charged carrier-ion complex was found to be influenced by irradiation. The effect is interpreted as an increase of the polarity (dielectric constant) of the membrane interior induced by the presence of polar products of lipid peroxidation. A combined action of OH- and HO2-radicals seems to be responsible for the phenomena. At large radiation doses (greater than or equal to 10(3) Gy) a reduction of the membrane conductance was observed. This is interpreted as an increased microviscosity, possibly caused by cross-linking of fatty acid residues. Ion carriers represent sensitive probes of radiation induced membrane damage. 相似文献
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The content of fluorescing products of lipid peroxidation (LFP) and hormone-stimulated lipolytic activity were determined in rat epididymal adipose tissue during a 29-day interval after whole-body gamma irradiation. An increase in LFP was accompanied by a decrease in lipolytic activity. It is suggested that these effects are interrelated and that the decrease in lipolysis in irradiated, semi fasting rats is an additional deteriorating factor leading to death in some animals. 相似文献