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排序方式: 共有684条查询结果,搜索用时 15 毫秒
1.
Gustav Schwab 《Planta》1936,25(4):579-606
Ohne ZusammenfassungMit 1 Textabbildung.Dissertation der Philosophischen Fakultät der Universität Leipzig. 相似文献
2.
Lipolysis of LDL with phospholipase A2 alters the expression of selected apoB-100 epitopes and the interaction of LDL with cells 总被引:2,自引:0,他引:2
Y Kleinman E S Krul M Burnes W Aronson B Pfleger G Schonfeld 《Journal of lipid research》1988,29(6):729-743
To assess the effects of perturbing the surface of low density lipoprotein (LDL) on the conformation of apoB-100, LDL (d 1.030-1.050 g/ml) isolated from normal subjects were treated with phospholipase A2 (PL-A2) for 0.5 to 15 min. The resulting P-LDL and concurrent control LDL (C-LDL) incubated without PL-A2 were isolated by gel permeation chromatography. Approximately 50% of LDL-phosphatidylcholine was hydrolyzed in 2 min and approximately 85% in 5 min. Lysophosphatidylcholine compounds (LPC) and free fatty acids (FFA) accumulated during lipolysis but most of the LPC and all of FFA could be removed by adding FFA-free albumin to the lipolysis mixtures. Immunoreactivities of P-LDL and C-LDL were evaluated in competitive radioimmunoassays, using a library of anti-human LDL monoclonal antibodies directed against the major regions of apoB-100 (the T4, T3, and T2 thrombin fragments). One epitope defined by monoclonal antibody 465B6C3 and localized near the carboxyl end of the apoB-100 molecule became less immunoreactive (ED 50s increased); three other epitopes on the T2 fragment near the LDL receptor recognition site and four epitopes localized towards the middle (T3) and amino terminal (T4) regions did not change. Altered immunoreactivities were not related to LPC and FFA contents. Thus, the conformation of apoB-100 was selectively altered by phospholipolysis. The interactions of P-LDL with cultured fibroblasts were grossly altered: P-LDL were bound nonspecifically to fibroblasts of both normal and homozygous familial hypercholesterolemic subjects and P-LDL were not degraded. LPC and FFA retained in LDL did not explain these alterations, nor did changes of epitope expression near the LDL receptor recognition site. It is likely that the apoB-100 aberrant cell interaction is due to loss of surface phospholipids and "uncovering" of core lipids that react nonspecifically with cell surface components. 相似文献
3.
Aortic accumulation and plasma clearance of beta-VLDL and HDL: effects of diet-induced hypercholesterolemia in rabbits 总被引:6,自引:0,他引:6
To assess the role of beta-VLDL in diet-induced atherogenesis, the in vivo metabolism and aortic accumulation of 125I-labeled beta-VLDL were investigated in cholesterol-fed rabbits and chow-fed controls. 125I-labeled HDL and 125I-labeled albumin were studied for comparison. The fractional catabolic rate of 125I-labeled beta-VLDL was reduced in cholesterol-fed rabbits (0.011 vs 0.139 hr-1), but due to the high endogenous pool, the total beta-VLDL flux was very high (13.1 vs less than 1.1 mg/kg per 24 hr). These results suggest that elevated levels of beta-VLDL during cholesterol feeding were due to an enhanced rate of synthesis, a finding confirmed in hypercholesterolemic rabbits subjected to plasmapheresis. Following acute reduction of plasma cholesterol by plasmapheresis, the quantitative increases in beta-VLDL cholesterol concentrations (210 to 364 mg/dl) over the subsequent 24 hr were in agreement with the rise calculated from the plasma clearance kinetics of 125I-labeled beta-VLDL (378 mg/dl per 24 hr). Aortic accumulation of beta-VLDL in hypercholesterolemic rabbits was increased greater than 15-fold over controls. Accumulation was predominantly in the intimal atheromatous lesions. The fractional catabolic rate of 125I-labeled HDL was increased during cholesterol feeding (0.037 vs 0.021 hr-1). A decreased rate of synthesis appeared to be responsible for the markedly depleted plasma HDL. HDL accumulation within the aorta was attenuated greater than 9-fold in cholesterol-fed rabbits compared to those fed normal chow. Plasma kinetics and aortic accumulation of 125I-labeled albumin were similar in hypercholesterolemic and control rabbits.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
4.
M C Blaufuss J I Gordon G Schonfeld A W Strauss D H Alpers 《The Journal of biological chemistry》1984,259(4):2452-2456
We have examined the biosynthesis of rat apolipoprotein C-III in the small intestine and liver. The primary translation product of its mRNA was recovered from wheat germ and ascites cell-free systems. Comparison of its NH2-terminal sequence with the NH2 terminus of plasma high density lipoprotein-associated apolipoprotein C-III showed that apo-C-III was initially synthesized as a preprotein with a 20 amino acid long NH2-terminal extension: Met-X-X-X-Met-Leu-Leu-X-X-Ala-Leu-X-Ala-Leu-Leu-Ala-X-Ala-X-Ala. Co-translational cleavage of the cell-free translation product by signal peptidase generated a polypeptide with the same NH2 terminus as the mature protein (X-Glu-X-Glu-Gly-Ser-Leu-Leu-Leu-Gly-Ser-Met). Therefore, this apolipoprotein does not undergo post-translational proteolytic processing like two other high density lipoprotein-affiliated proteins, proapo-A-I and proapo-A-II. The mRNA encoding apolipoprotein C-III comprises 0.4% of the translatable RNA species in adult rat liver and 0.14% of the translatable RNA species in small intestinal epithelium. Acute fat feeding with a triglyceride meal resulted in a 2-fold increase in intestinal preapo-C-III mRNA accumulation but no change in the levels of preproapo-A-I mRNA. Thus, the acute response of the apo-A-I and C-III genes to triacylglycerol absorption differs. 相似文献
5.
Amira Klip Denise Walker Kathleen J. Ransome Dean W. Schroer Gustav E. Lienhard 《Archives of biochemistry and biophysics》1983,226(1):198-205
The glucose transporter in the plasma membrane of rat skeletal muscle has been identified by two approaches. In one, the transporter was detected as the polypeptide that was differentially labeled by photolysis with [3H]cytochalasin B in the presence of l- and d-glucose. [3H]Cytochalasin B is a high-affinity ligand for the transporter that is displaced by d-glucose. In the other, the transporter was detected by means of its reaction with rabbit antibodies against the purified glucose transporter from human erythrocytes. By both procedures, the transporter was found to be a polypeptide with a mobility corresponding to a molecular weight of 45,000–50,000 upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis. 相似文献
6.
Differential reactivity of human low density lipoproteins with monoclonal antibodies 总被引:1,自引:0,他引:1
The immunoreactivities of LDL (low density lipoprotein) samples obtained from a variety of subjects were analyzed by comparing their capacities to compete with 125I-labeled LDL for binding to various monoclonal anti-LDL antibodies in competitive binding assays. A marked variation in epitope expression was observed. In comparison to an LDL standard, different preparations exhibited immunoreactivities (expressed as apparent apoB content) ranging from 30 to 400% of the LDL standard. Some epitopes were much more uniformly expressed than others. The number of epitopes expressed in different LDL preparations appeared to be related to the percentage composition of various lipid constituents in LDL. The results support the hypothesis that the epitope expression of apoB is modulated by the composition of the lipids associated with it. 相似文献
7.
HETEROGENEOUS DISTRIBUTION OF ENZYMES IN SUBMICROSOMAL MEMBRANE FRAGMENTS 总被引:14,自引:9,他引:5
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Peter R. Dallman Gustav Dallner Anders Bergstrand Lars Ernster 《The Journal of cell biology》1969,41(2):357-377
Microsomal membranes are postulated to contain either a homogeneous arrangement of individual enzymes or groupings of functionally related enzymes. In the present study we attempt to distinguish between these hypotheses in subfractions of rough microsomes from rat liver. After sonication, the individual vesicles that make up the rough-membrane fraction average less than 1/100 of their previous mass. The vesicles in the sonicated suspension are fractionated roughly according to size on a continuous sucrose gradient. Enzyme activity or concentration in fractions of the gradient is expressed on a phospholipid basis. Fractions containing primarily small vesicles differ from those containing larger vesicles in a manner suggesting a certain degree of separation of NADH-linked from NADPH-linked enzymes. NADH-ferricyanide reductase, NADH-cytochrome c reductase and cytochrome b5 are most concentrated within the large vesicles in the lowest third of the gradient. In contrast, NADPH-cytochrome c reductase and cytochrome P-450 are found in highest concentration in the small vesicles that make up the upper third of the gradient. The results suggest a nonrandom distribution of these two enzyme groups in the membranes of the endoplasmic reticulum. 相似文献
8.
Ohne Zusammenfassung
Mit 12 Textabbildungen 相似文献
9.
Lipid Composition in Scrapie-Infected Mouse Brain: Prion Infection Increases the Levels of Dolichyl Phosphate and Ubiquinone 总被引:1,自引:0,他引:1
Zhizhong Guan Magnus Söderberg Pavel Sindelar Stanley B. Prusiner †Krister Kristensson Gustav Dallner 《Journal of neurochemistry》1996,66(1):277-285
Abstract: The neutral and phospholipid composition of mouse brain infected with scrapie prions was investigated. During the later stages of this disease, the level of dolichol decreased by 30% whereas the level of dolichyl phosphate increased by 30%. In terminally ill mice, there was also a 2.5-fold increase in both total ubiquinone and its reduced form. Furthermore, α-tocopherol was elevated at this stage by 50%. In contrast, no changes were observed in phospholipid amount, in phospholipid composition, and in phosphatidylethanolamine plasmalogen content during the entire disease process. The fatty acid and aldehyde composition of individual phospholipids remained unaltered as well. No modifications could be detected in cholesterol content. Thus, the majority of membrane lipids in scrapie-infected mouse brain are modified in neither quantity nor structure, but specific changes occur to a few polyisoprenoid lipids. This specificity indicates that, although prions accumulate in lysosomes, the infection process is not associated with a general membrane destruction caused by lysosomal enzyme leakage. 相似文献
10.
Jrn Elsner Johannes Norgauer Gustav J. Dobos Andreas Emmendrffer Erwin Schpf Alexander Kapp Joachim Roesler 《Journal of cellular physiology》1993,157(3):637-643
Flow cytometric analyses were performed to study intracellular single-cell calcium transients ([Ca2+]i) in suspended human neutrophils during the initial phase of N-formyl peptide stimulation. Thereby, two neutrophil populations became apparent. Early maximally Ca2+-responding (high fluorescence) neutrophils and not-yet Ca2+-responding (low fluorescence) neutrophils, but no neutrophils with intermediate levels of [Ca2+]i, were detected. Within 7 s the number of low fluorescence neutrophils decreased and the number of high fluorescence neutrophils increased maximally. This suggests that [Ca2+]i transients occurred abruptly in individual neutrophils within a time interval below 1 s. At lower N-formyl peptide concentrations the lag times of individual neutrophils and the interval time of maximal activation of the [Ca2+]i-responding neutrophil population increased, however the percentage of [Ca2+]i-responding cells decreased. Surprisingly, no influence of the N-formyl peptide concentration on the [Ca2+]i-induced fluorescence signal of the individual cell was observed: it was always in an almost maximal range or not responding. In parallel, binding studies performed with fluorescein-labeled N-formyl peptide revealed that the heterogeneity of [Ca2+]i-responding cells cannot be explained by different receptor occupancy. In summary, this study demonstrates that [Ca2+]i transients induced by N-formyl peptides in suspended individual human neutrophils occur very rapidly in an almost “all-or-none manner” and that the mean increasing fluorescence signal of a calcium indicator within a whole neutrophil population results from varying lag times of the individual cells, rather than from the mean simultaneous progress of many cells. © 1993 Wiley-Liss, Inc. 相似文献