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1.
Partition coefficients of the insecticide γ-1,2,3,4,5,6-hexachlorocyclohexane (trivially, lindane) were determined in model and native membranes. Partition in egg phosphatidylcholine bilayers decreases linearly with temperature, over a range (10–40°C) at which the lipid is in the liquid-crystalline state. Addition of 50 mol% cholesterol dramatically decreases partition (2100 falls to 100, at 10°C) and abolishes the temperature dependence. First-order phase transitions of dimyristoyl-, dipalmitoyl- and distearoylphosphatidylcholines (DMPC, DPPC and DSPC) are accompanied by a sharp increase in lindane partition. Apparently, the insecticide is easily accommodated in bilayers of short-aliphatic-chain lipids, since the partitions were 2450, 600 and 50 in DMPC, DPPC and DSPC, respectively, at temperatures 10 Cdeg below the midpoint of their transitions. The lindane partition sequence in native membranes is as follows: mitochondria, sarcoplasmic reticulum, myelin, brain microsomes and erythrocytes. This sequence correlates reasonably well with the relative content of cholesterol and is similar in liposomes of total extracted lipids, although the absolute partitions showed decreased values. Therefore, the presence of proteins in native membranes contributes to the insecticide partition, probably by favouring its interaction with lipids. 相似文献
2.
Partition of DDT in synthetic and native membranes 总被引:3,自引:0,他引:3
Partition of DDT (2,2-bis(p-chlorophenyl)-1,1,1-trichloroethane) was determined in artificial and native membranes. Partition in egg phosphatidylcholine of about 260 000 is independent of temperature over the range from 10 to 40 degrees C, in which the lipid is in the liquid-crystalline state. Incorporation of 50 mol% cholesterol decreases DDT partition to about 120 000. First-order phase transitions of dimyristoyl-, dipalmitoyl- and distearoylphosphatidylcholines (DMPC, DPPC and DSPC) are accompanied by a sharp increase in DDT partitioning. Partition decreases symmetrically in the temperature ranges to both sides of the phase transition. The insecticide is preferentially accommodated in bilayers of short-aliphatic-chain lipids, since the partitions were 336 000, 180 000 and 88 000 in DMPC, DPPC and DSPC, respectively, at temperatures 10 Cdeg below the midpoint of their transitions. Partition values in native membranes decrease sequentially as follows: sarcoplasmic reticulum, mitochondria, myelin, brain microsomes and erythrocytes. This sequence is similar to that observed in related liposomes of total extracted lipids, although the absolute partitions showed decreased values. Partition of DDT in native membranes exhibits a negative temperature coefficient not apparent in related lipid dispersions. The effect of intrinsic membrane cholesterol on partition of DDT was also investigated. 相似文献
3.
Effect of short-chain primary alcohols on fluidity and activity of sarcoplasmic reticulum membranes 总被引:1,自引:0,他引:1
Intramolecular excimer formation with the fluorescent probe 1,3-di(1-pyrenyl)propane, differential scanning calorimetry, and X-ray diffraction were used to assess the effect of ethanol, 1-butanol, and 1-hexanol on the bilayer organization in model membranes, sarcoplasmic reticulum (SR) lipids and native SR membranes. These alcohols have fluidizing effects on membranes and lower the main transition temperature of dimyristoylphosphatidylcholine (DMPC), but only 1-hexanol alters the cooperativity of the phase transition and significantly increases the thickness of DMPC bilayers. The interaction of the three alcohols with the SR Ca2+ pump was also investigated. Hydrolysis of ATP and coupled Ca2+ uptake are differently sensitive to the three alcohols. Whereas ethanol and 1-butanol inhibited the Ca2+ uptake, 1-hexanol stimulated it. Nevertheless, the energetic efficiency of the pump (Ca2+/ATP) is not significantly affected by ethanol or 1-hexanol, but uncoupling was observed with 1-butanol at high concentrations. The different effects of alcohols on the activity of SR membranes rule out an unitary mechanism of action on the basis of fluidity changes induced in the lipid bilayer. Depending on the chain length, the alcohols interact with the SR membranes in different domains, perturbing differently the Ca2+-pump activity. 相似文献
4.
B A Chapman J S Wilson P W Colley R C Pirola J B Somer 《Biochemical and biophysical research communications》1983,115(3):771-776
Stimulation of the exocrine pancreas is associated with marked changes in pancreatic phospholipid metabolism. It has been previously established that de novo synthesis of phospholipids constitutes part of this "phospholipid effect". This study has demonstrated that in vitro stimulation of the rat pancreas utilising bethanecol and pancreozymin results in increased incorporation of labelled glucose into phosphatidyl inositol and, to a lesser extent, other phospholipids, suggesting increased de novo synthesis of these compounds. However, secretin which is believed to act via a different intracellular pathway, did not exert such an effect. The relevance of this animal model is indicated by the demonstration of increased incorporation of labelled glucose into phospholipids of human pancreas stimulated in vitro by bethanecol or sincalide (the active carboxy terminal octapeptide of pancreozymin). 相似文献
5.
B A Pirola F Mayer I A Borthwick G Srivastava B K May W H Elliott 《European journal of biochemistry》1984,144(3):577-579
The structure of chick embryo liver 5-aminolaevulinate synthase has been examined by electron microscopic studies using negative staining. From the different projections of the enzyme particles observed in electron micrographs, a model for the enzyme molecule has been proposed. In this model, an enzyme molecule consists of two curved and identical subunits associated in opposite polarities. From the dimensions of an enzyme molecule subunit measured from electron micrographs, the relative molecular mass of each subunit is estimated to be 70 000. 相似文献
6.
V M Madeira 《Biochimica et biophysica acta》1977,499(2):202-211
1. Plasma membranes were isolated from ascites hepatoma AH-130 and rat livers with or without partial hepatectomy or bile duct ligation. Reciprocal manifestations of two marker enzymes for plasma membranes were observed in these membrane preparations; alkaline phosphatase activity was found much higher in the hepatoma membrane than in any preparations of the liver membranes, whereas 5'-nucleotidase activity was much lower in the former than in the latter. 2. Effects of lectins and anti-plasma membrane antiserum on these two marker enzymes were examined. The results showed that about 50% of apparent activity of 5'-nucleotidase found in the hepatoma membrane was exhibited by alkaline phosphatase. 3. Localizations of alkaline phosphatase and 5'-nucleotidase in polyacrylamide gels after electrophoresis were demonstrated using 5'-AMP and 5-Br, 4-Cl-indoxylphosphate as substrate. There was a difference in electrophoretic mobility between the alkaline phosphatase of the hepatoma and that of the liver. 相似文献
7.
V M Madeira 《Archives of biochemistry and biophysics》1979,193(1):22-27
The pH indicator, bromothymol blue, was incorporated into sarcoplasmic reticulum vesicles which bind more than 90% of the total added dye. The sequestered dye does not respond to changes in external pH upon addition of acid to the medium, since the decrease of absorbance at 616 nm is very slow. The absorbance of sequestered dye at 616 nm increases suddenly after triggering the transport of Ca2+ by ATP at a rate much higher than that of Ca2+ uptake, and declines when Ca2+ has been accumulated. When the uptake of Ca2+ is followed in the presence of oxalate, the absorbance of the indicator declines after the first phase of Ca2+ uptake. The results suggest that a transient alkalinization occurs rapidly inside the vesicles and reflects the formation of a transmembrane proton gradient responsible for sustaining the Ca2+ transport. 相似文献
8.
The translational diffusion of bovine rhodopsin, the Ca2+-activated adenosinetriphosphatase of rabbit muscle sarcoplasmic reticulum, and the acetylcholine receptor monomer of Torpedo marmorata has been examined at a high dilution (molar ratios of lipid/protein greater than or equal to 3000/1) in liquid-crystalline phase phospholipid bilayer membranes by using the fluorescence recovery after photobleaching technique. These integral membrane proteins having molecular weights of about 37 000 for rhodopsin, about 100 000 for the adenosinetriphosphatase, and about 250 000 for the acetylcholine receptor were reconstituted into membranes of dimyristoylphosphatidylcholine (rhodopsin and acetylcholine receptor), soybean lipids (acetylcholine receptor), and a total lipid extract of rabbit muscle sarcoplasmic reticulum (adenosinetriphosphatase). The translational diffusion coefficients of all the proteins at 310 K were found to be in the range (1-3) X 10(-8) cm2/s. In consideration of the sizes of the membrane-bound portions of these proteins, this result is in agreement with the weak dependence of the translational diffusion coefficient upon diffusing particle size predicted by continuum fluid hydrodynamic models for the diffusion in membranes [Saffman, P. G., & Delbrück, M. (1975) Proc. Natl. Acad. Sci. U.S.A. 72, 3111-3113]. Lipid diffusion was also examined in th same lipid bilayers with the fluorescent lipid derivative N-(7-nitro-2,1,3-benzoxadiazol-4-yl)dimyristoylphosphatidylethanolamine. The translational diffusion coefficient for this lipid derivative was found to be in the range (9-14) X 10(-8) cm2/s at 310 K. In consideration of the dimensions of the lipid molecule, this value for the lipid diffusion coefficient is in agreement with the continuum fluid hydrodynamic model only if a near-complete slip boundary condition is assumed at the bilayer midplane. Alternatively, kinetic diffusion models [Tr?uble, H., & Sackmann. E. (1972) J. Am. Chem. Soc. 94, 4499-4510] may have to be invoked to explain the lipid diffusion behavior. 相似文献
9.
10.
Rates of nutrient release byMysis relicta in Lake Michigan were measured on five nights at a 45-m station near Milwaukee, Wisconsin, U.S.A., in the summer of 1977. Nocturnal vertical migrations of the mysids were monitored with both echosounder tracings and vertical net tows. Estimates of the total areal dry mass of the mysids ranged from 600 to 1 820 mg m–2. Rates of release of dissolved reactive phosphorus, total phosphorus, ammonia, and urea were measured in dark incubations on shipboard. Excretion experiments were initiated immediately after mysids were collected from each of several vertical net hauls. The depths of maximum mysid densities corresponded approximately with a deep phytoplankton peak located in the vicinity of the thermocline. Semiquantitative demands for N and P by phytoplankton within this peak were obtained from14C estimates of primary production from a previous study, assuming a constant C:N:P ratio for the algae. These algal nutrient demands were compared to potential N and P release by the mysids to obtain a first approximation of the relative rates of nutrient supply and demand for the field phytoplankton populations. Our analysis indicates that mysids may directly supply about 1–10% of the daily N and P demands of the phytoplankton in the deep peak. However, indirect interactions betweenMysis relicta and other organisms, such as small zooplankton and fishes, could be major factors in nutrient recycling within the metalimnion and subthermocline region of Lake Michigan.Contribution No. 238, Center for Great Lakes Studies, University of Wisconsin-Milwaukee, Wisconsin.Contribution No. 238, Center for Great Lakes Studies, University of Wisconsin-Milwaukee, Wisconsin. 相似文献