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排序方式: 共有89条查询结果,搜索用时 15 毫秒
1.
THE METABOLISM OF CHYLOMICRON CHOLESTERYL ESTER IN RAT LIVER : A Combined Radioautographic-Electron Microscopic and Biochemical Study 总被引:13,自引:1,他引:12 下载免费PDF全文
Olga Stein Yechezkiel Stein Dewitt S. Goodman Noel H. Fidge 《The Journal of cell biology》1969,43(3):410-431
Chylomicrons containing labeled cholesterol, mainly (70%) present as cholesteryl ester, were injected intravenously into intact rats, and samples of liver were obtained 27–210 min later. Most (58–75%) of the injected label was recovered in the liver after 27–75 min. Hepatic uptake occurred without hydrolysis of the labeled cholesteryl ester. In separate experiments, in vitro perfusion of livers of similarly treated rats for 30–35 min washed out only 3–9% of the labeled sterol. Samples of liver and small intestine were prepared for electron microscopy with Aquon as the dehydrating agent. Good retention (70% or more) of labeled cholesterol and satisfactory preservation of ultrastructure were obtained. After 30 min, the radioautographic reaction was localized mainly over the region of the cell boundary of the parenchymal liver cells, with fewer grains being present over intracellular organelles. At later time intervals, when considerable hydrolysis of the labeled cholesteryl ester had occurred, the radioautographic reaction was more evenly distributed. Phagocytosed labeled lipid was seen in Kupffer cells after the larger lipid load; phagocytosis by parenchymal cells was not seen. In other experiments, cholesteryl ester hydrolase activity was found in all subcellular fractions, the microsome and plasma membrane fractions showing the highest activity per mg protein. The mechanism of cholesteryl ester transport into the liver cell may involve: (1) hydrolysis at the cell surface; or (2) slow entry of intact molecules followed by intracellular hydrolysis of the ester bond. 相似文献
2.
DNA sequences were determined for three to five alleles of the bride-of-
sevenless (boss) gene in each of four species of Drosophila. The product of
boss is a transmembrane receptor for a ligand coded by the sevenless gene
that triggers differentiation of the R7 photoreceptor cell in the compound
eye. Population parameters affecting the rate and pattern of molecular
evolution of boss were estimated from the multinomial configurations of
nucleotide polymorphisms of synonymous codons. The time of divergence
between D. melanogaster and D. simulans was estimated as approximately 1
Myr, that between D. teissieri and D. yakuba as approximately 0.75 Myr, and
that between the two pairs of sibling species as approximately 2 Myr. (The
boss genes themselves have estimated divergence times approximately 50%
greater than the species divergence times.) The effective size of the
species was estimated as approximately 5 x 10(6), and the average mutation
rate was estimated as 1-2 x 10(-9)/nucleotide/generation. The ratio of
amino acid polymorphisms within species to fixed differences between
species suggests that approximately 25% of all possible single-step amino
acid replacements in the boss gene product may be selectively neutral or
nearly neutral. The data also imply that random genetic drift has been
responsible for virtually all of the observed differences in the portion of
the boss gene analyzed among the four species.
相似文献
3.
Hybertson Brooks M.; Bursten Stuart L.; Leff Jonathan A.; Lee Young M.; Jepson Eric K.; Dewitt Chris R.; Zagorski John; Cho Hyun G.; Repine John E. 《Journal of applied physiology》1997,82(1):226-232
Hybertson, Brooks M., Stuart L. Bursten, Jonathan A. Leff,Young M. Lee, Eric K. Jepson, Chris R. Dewitt, John Zagorski, Hyun G. Cho, and John E. Repine. Lisofylline prevents leak, but not neutrophil accumulation, in lungs of rats given IL-1intratracheally. J. Appl. Physiol.82(1): 226-232, 1997.Interleukin-1 (IL-1) is increased in lunglavages from patients with the acute respiratory distress syndrome, andadministering IL-1 intratracheally causes neutrophil accumulation and aneutrophil-dependent oxidative leak in lungs of rats. In the presentstudy, we found that rats pretreated intraperitoneally with lisofylline[(R)-1-(5-hydroxyhexyl)-3,7-dimethylxanthine (LSF)], an inhibitor of lysophosphatidic acid acyl transferase, which reduces the production of unsaturated phosphatidic acid species,did not develop the lung leak or the related ultrastructural abnormalities that occur after intratracheal administration of IL-1.However, rats pretreated with LSF and then given IL-1 intratracheally did develop the same elevations of lung lavage cytokine-induced neutrophil chemoattractant (CINC) levels and the same increased numbersof lung lavage neutrophils as rats given IL-1 intratracheally. Lungs ofrats given IL-1 intratracheally also had increased unsaturated phosphatidic acid and free acyl (linoleate, linolenate) concentrations compared with untreated rats, and these lipid responses were prevented by pretreatment with LSF. Our results reveal that LSF decreases lungleak and lung lipid alterations without decreasing neutrophil accumulation or lung lavage CINC increases in rats given IL-1 intratracheally. 相似文献
4.
The contractile basis of amoeboid movement: V. The control of gelation, solation, and contraction in extracts from dictyostelium discoideum 总被引:29,自引:22,他引:7 下载免费PDF全文
Motile extracts have been prepared from Dictyostelium discoideum by homogenization and differential centrifugation at 4 degrees C in a stabilization solution (60). These extracts gelled on warming to 25 degrees Celsius and contracted in response to micromolar Ca++ or a pH in excess of 7.0. Optimal gelation occurred in a solution containing 2.5 mM ethylene glycol-bis (β-aminoethyl ether)N,N,N',N'-tetraacetate (EGTA), 2.5 mM piperazine-N-N'-bis [2-ethane sulfonic acid] (PIPES), 1 mM MgC1(2), 1 mM ATP, and 20 mM KCI at ph 7.0 (relaxation solution), while micromolar levels of Ca++ inhibited gelation. Conditions that solated the gel elicited contraction of extracts containing myosin. This was true regardless of whether chemical (micromolar Ca++, pH >7.0, cytochalasin B, elevated concentrations of KCI, MgC1(2), and sucrose) or physical (pressure, mechanical stress, and cold) means were used to induce solation. Myosin was definitely required for contraction. During Ca++-or pH-elicited contraction: (a) actin, myosin, and a 95,000-dalton polypeptide were concentrated in the contracted extract; (b) the gelation activity was recovered in the material sqeezed out the contracting extract;(c) electron microscopy demonstrated that the number of free, recognizable F-actin filaments increased; (d) the actomyosin MgATPase activity was stimulated by 4- to 10-fold. In the absense of myosin the Dictyostelium extract did not contract, while gelation proceeded normally. During solation of the gel in the absense of myosin: (a) electron microscopy demonstrated that the number of free, recognizable F- actin filaments increased; (b) solation-dependent contraction of the extract and the Ca++-stimulated MgATPase activity were reconstituted by adding puried Dictyostelium myosin. Actin purified from the Dictyostelium extract did not gel (at 2 mg/ml), while low concentrations of actin (0.7-2 mg/ml) that contained several contaminating components underwent rapid Ca++ regulated gelation. These results indicated : (a) gelation in Dictyostelium extracts involves a specific Ca++-sensitive interaction between actin and several other components; (b) myosin is an absolute requirement for contraction of the extract; (c) actin-myosin interactions capable of producing force for movement are prevented in the gel, while solation of the gel by either physical or chemical means results in the release of F-actin capable of interaction with myosin and subsequent contraction. The effectiveness of physical agents in producting contraction suggests that the regulation of contraction by the gel is structural in nature. 相似文献
5.
Geigert J Neidleman SL Liu TN Dewitt SK Panschar BM Dalietos DJ Siegel ER 《Applied and environmental microbiology》1983,45(3):1148-1149
The relative activity of Flavobacterium whole cells on the enzymatic synthesis of epoxides from alpha,beta-chlorohydrins, -bromohydrins, and -iodohydrins is described. 相似文献
6.
Henry C. Orr Kyle H. Sibinovic Peter G. Probst H. Donald Hochstein Dewitt C. Littlejohn 《In vitro cellular & developmental biology. Plant》1975,11(4):230-233
Summary Bacteriological tests were made on 24 lots of unfiltered calf serum collected for subsequent use as a component of tissue
culture media. The examination included the isolation and identification of bacteria, assay of phages, and demonstration of
endotoxin material. Only Gram-positive bacteria were isolated and 96% of the sera were contaminated with bacteria. The prevalent
strains of bacteria found wereBacillus species and streptococci and 63% of the sera coagulatedLimulus amebocyte lysate. More than 90% of the lots contained phages demonstrable with the C-3000 strain ofEscherichia coli. Only one lot of the serum was found to be free from bacteria, phages, and endotoxin by the tests used. 相似文献
7.
V KW Wong T Li B YK Law E DL Ma N C Yip F Michelangeli C KM Law M M Zhang K YC Lam P L Chan L Liu 《Cell death & disease》2013,4(7):e720
Autophagy is an important cellular process that controls cells in a normal homeostatic state by recycling nutrients to maintain cellular energy levels for cell survival via the turnover of proteins and damaged organelles. However, persistent activation of autophagy can lead to excessive depletion of cellular organelles and essential proteins, leading to caspase-independent autophagic cell death. As such, inducing cell death through this autophagic mechanism could be an alternative approach to the treatment of cancers. Recently, we have identified a novel autophagic inducer, saikosaponin-d (Ssd), from a medicinal plant that induces autophagy in various types of cancer cells through the formation of autophagosomes as measured by GFP-LC3 puncta formation. By computational virtual docking analysis, biochemical assays and advanced live-cell imaging techniques, Ssd was shown to increase cytosolic calcium level via direct inhibition of sarcoplasmic/endoplasmic reticulum Ca2+ ATPase pump, leading to autophagy induction through the activation of the Ca2+/calmodulin-dependent kinase kinase–AMP-activated protein kinase–mammalian target of rapamycin pathway. In addition, Ssd treatment causes the disruption of calcium homeostasis, which induces endoplasmic reticulum stress as well as the unfolded protein responses pathway. Ssd also proved to be a potent cytotoxic agent in apoptosis-defective or apoptosis-resistant mouse embryonic fibroblast cells, which either lack caspases 3, 7 or 8 or had the Bax-Bak double knockout. These results provide a detailed understanding of the mechanism of action of Ssd, as a novel autophagic inducer, which has the potential of being developed into an anti-cancer agent for targeting apoptosis-resistant cancer cells. 相似文献
8.
High rate of DNA loss in the Drosophila melanogaster and Drosophila virilis species groups 总被引:6,自引:3,他引:3
We recently proposed that patterns of evolution of non-LTR
retrotransposable elements can be used to study patterns of spontaneous
mutation. Transposition of non-LTR retrotransposable elements commonly
results in creation of 5' truncated, "dead-on-arrival" copies. These
inactive copies are effectively pseudogenes and, according to the neutral
theory, their molecular evolution ought to reflect rates and patterns of
spontaneous mutation. Maximum parsimony can be used to separate the
evolution of active lineages of a non-LTR element from the fate of the
"dead-on-arrival" insertions and to directly assess the relative
frequencies of different types of spontaneous mutations. We applied this
approach using a non-LTR element, Helena, in the Drosophila virilis group
and have demonstrated a surprisingly high incidence of large deletions and
the virtual absence of insertions. Based on these results, we suggested
that Drosophila in general may exhibit a high rate of spontaneous large
deletions and have hypothesized that such a high rate of DNA loss may help
to explain the puzzling dearth of bona fide pseudogenes in Drosophila. We
also speculated that variation in the rate of spontaneous deletion may
contribute to the divergence of genome size in different taxa by affecting
the amount of superfluous "junk" DNA such as, for example, pseudogenes or
long introns. In this paper, we extend our analysis to the D. melanogaster
subgroup, which last shared a common ancestor with the D. virilis group
approximately 40 MYA. In a different region of the same transposable
element, Helena, we demonstrate that inactive copies accumulate deletions
in species of the D. melanogaster subgroup at a rate very similar to that
of the D. virilis group. These results strongly suggest that the high rate
of DNA loss is a general feature of Drosophila and not a peculiar property
of a particular stretch of DNA in a particular species group.
相似文献
9.
The costs and limits of phenotypic plasticity are thought to have important ecological and evolutionary consequences, yet they are not as well understood as the benefits of plasticity. At least nine ideas exist regarding how plasticity may be costly or limited, but these have rarely been discussed together. The most commonly discussed cost is that of maintaining the sensory and regulatory machinery needed for plasticity, which may require energy and material expenses. A frequently considered limit to the benefit of plasticity is that the environmental cues guiding plastic development can be unreliable. Such costs and limits have recently been included in theoretical models and, perhaps more importantly, relevant empirical studies now have emerged. Despite the current interest in costs and limits of plasticity, several lines of reasoning suggest that they might be difficult to demonstrate. 相似文献