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1.
Asymmetry in the renewal of molecular classes of phosphatidylcholine in the rat-erythrocyte membrane
- 1. 1. Rat-blood phospholipids were labeled in vivo with [32P]phosphate. The erythrocytes were treated with phospholipase A2 plus sphingomyelinase to discriminate between the labeling patterns of the phospholipids from the inner and outer layer of the membrane.
- 2. 2. The specific activities of the more unsaturated classes of phosphatidylcholine were higher in the outer layer of the erythrocyte membrane than in the inner layer. The disaturated class, however, had the highest specific activity in the inner layer.
- 3. 3. After incubating 32P-labeled erythrocytes in unlabeled plasma, the labeling pattern recovered in the molecular classes of plasma phosphatidylcholine was very similar to that of the phosphatidylcholines in the outer layer of the erythrocyte membrane.
- 4. 4. It is proposed that the exchange of phosphatidylcholines between plasma and the outer layer of the erythrocyte is mainly responsible for the renewal of the unsaturated phosphatidylcholines of the erythrocyte, and that the acylation activity of the erythrocyte is directed towards the formation of disaturated phosphatidylcholines at the inside of the membrane.
Keywords: Phosphatidylcholine; Asymmetry; Molecular classes; Metabolism; Erythrocyte membrane; (Rat) 相似文献
2.
- 1. 1. Anesthetic alcohols (pentanol, hexanol and heptanol) were found to increase the fluidity of red cell membrane lipids as monitored by the fluorescence depolarization of diphenylhexatriene. The relative potency of the alcohols was found to be parallel to their relative membrane/water partition coefficients.
- 2. 2. Hexanol had biphasic effect on erythritol uptake by simple diffusion by red cells. At concentrations less than 9 mM, hexanol had no significant effect. At concentrations greater than 9 mM, there was an approximately linear increase in erythritol permeability with increasing alcohol concentration.
- 3. 3. The facilitated transport of uridine was markedly inhibited by hexanol. Hexanol at 6 mM produced a 65% inhibition of uridine (4 mM) uptake. Hexanol decreased both the apparent Km and V values for the equilibrium exchange of uridine.
- 4. 4. The facilitated transport of galactose was only slightly inhibited by hexanol.
- 5. 5. Hexanol was without effect on the passive and active fluxes of Na+ and K+ in red cells with altered cation contents. Cells that were slightly depleted of K+ and cells that were highly K+-depleted were both insensitive to hexanol.
Keywords: Anesthetic alcohol; Transport; (Human erythrocyte membrane) 相似文献
3.
4.
The human erythrocyte nucleoside and glucose transporters are both band 4.5 membrane polypeptides. 总被引:2,自引:1,他引:1
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Human erythrocyte membranes and partially purified nucleoside transporter (band 4.5 and 7) were photoaffinity labelled with 3H-labelled 6-[(4-nitrobenzyl)thio]-9-beta-D-ribofuranosylpurine under equilibrium binding conditions. Band 4.5 was the major site of radiolabelling in both preparations. These experiments provide additional evidence to implicate band 4.5 polypeptides in nucleoside permeation, proteins previously shown to be involved in hexose transport. 相似文献
5.
Dual effect of membrane cholesterol on simple and mediated transport processes in human erythrocytes
The influence of cholesterol on simple and facilitated transport processes across the membrane of intact human erythrocytes was studied after graded depletion or enrichment of membrane cholesterol by incubation of the cells in phospholipid or phospholipid/cholesterol suspensions.
- 1. 1. The carrier-mediated transfer of L-lactate and of L-arabinose proved to be enhanced by cholesterol. In the case of L-lactate, a decrease in Km seems to be involved in this effect. In contrast, the self-exchange of SO42−, mediated by the inorganic anion-exchange system, and the simple diffusion of erythritol via the lipid phase of the membrane are inhibited by cholesterol.
- 2. 2. Reversibility of these two opposite effects of cholesterol was demonstrated by measurements on cells depleted again after cholesterol enrichment and enriched again after previous depletion.
- 3. 3. Certain phospholipids used for preparing the lipid dispersions that are required for cholesterol variation have effects on permeability of their own, due, for example, to traces of contaminants. A discrimination of such artifacts from the effects of cholesterol is only possible by demonstrating reversibility.
- 4. 4. The opposite effects of cholesterol on various facilitated transfer processes, which have a correlation in the opposite effects of other modifications of the membrane lipid phase (Deuticke, B., Grunze, M. and Haest, C.W.M. (1979) Alfred Benzon Symposium 14, Munksgaard, Copenhagen, in the press), are indicative of different types of lipid-protein interaction in the erythrocyte membrane.
Keywords: Cholesterol; Permeability; Anion transport; Monosaccharide; Monocarboxylate (Erythrocyte membrane) 相似文献
6.
Acyclovir transport into human erythrocytes 总被引:2,自引:0,他引:2
W B Mahony B A Domin R T McConnell T P Zimmerman 《The Journal of biological chemistry》1988,263(19):9285-9291
The mechanism of transport of the antiviral agent acyclovir (ACV) into human erythrocytes has been investigated. Initial velocities of ACV influx were determined with an "inhibitor-stop" assay that used papaverine to inhibit ACV influx rapidly and completely. ACV influx was nonconcentrative and appeared to be rate-saturable with a Km of 260 +/- 20 microM (n = 8). However, two lines of evidence indicate that ACV permeates the erythrocyte membrane by means other than the nucleoside transport system: 1) potent inhibitors (1.0 microM) of nucleoside transport (dipyridamole, 6-[(4-nitrobenzyl)thio]-9-beta-D-ribofuranosylpurine, and dilazep) had little (less than 8% inhibition) or no effect upon the influx of 5.0 microM ACV; and 2) a 100-fold molar excess of several purine and pyrimidine nucleosides had no inhibitory effect upon the influx of 1.0 microM ACV. However, ACV transport was inhibited competitively by adenine (Ki = 9.5 microM), guanine (Ki = 25 microM), and hypoxanthine (Ki = 180 microM). Conversely, ACV was a competitive inhibitor (Ki = 240-280 microM) of the transport of adenine (Km = 13 microM), guanine (Km = 37 microM), and hypoxanthine (Km = 180 microM). Desciclovir and ganciclovir, two compounds related structurally to ACV, were also found to be competitive inhibitors of acyclovir influx (Ki = 1.7 and 1.5 mM, respectively). These results indicate that ACV enters human erythrocytes chiefly via the same nucleobase carrier that transports adenine, guanine, and hypoxanthine. 相似文献
7.
8.
- 1. 1. The application of the 13C-NMR technique to the study of lipid polymorphism is described for various model and biological membranes.
- 2. 2. The 13C-NMR line-width of various resonances of the lipid molecule are sensitive to the bilayer hexagonal and the bilayer ‘isotropic’ phase transition. The latter transition in some cases is accompanied by the occurrence of lipidic particles as detected by freeze-fracturing. Thus, specific 13C-labeling experiments allow the study of the individual phase behaviour of lipids in mixed lipid systems.
- 3. 3. In diet experiments using rats, the choline group of phosphatidylcholine present in erythrocyte, endoplasmic and sarcoplasmic reticulum membranes could be specifically 13C-labeled. The 13C line-widths of the resonance from the erythrocyte are typical for a lamellar arrangement of the membrane lipids. In strong contrast, the line-width observed at 37°C for the endoplasmic and sarcoplasmic reticulum membranes is much smaller, typical of the isotropic phases observed in model membranes. In isolated rat liver microsomes and liver slices, the 13C line-width is strongly temperature dependent. At lower temperatures the line-widths strongly increase towards values typical of lipids in a bilayer structure.
Keywords: 13C-NMR; Lipid polymorphism; Endoplasmic reticulum; Sarcoplasmic reticulum; (Rat liver) 相似文献