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排序方式: 共有318条查询结果,搜索用时 46 毫秒
1.
Quantitation of free sphingosine in liver by high-performance liquid chromatography 总被引:10,自引:0,他引:10
A H Merrill E Wang R E Mullins W C Jamison S Nimkar D C Liotta 《Analytical biochemistry》1988,171(2):373-381
Conditions were established for the extraction of free sphingosine from liver and the separation and quantitation of this and other long-chain (sphingoid) bases (e.g., sphingosine, sphinganine, phytosphingosine, and homologs) by reverse-phase high-performance liquid chromatography (HPLC). The long-chain bases were extracted with chloroform and methanol and then treated with base to remove interfering lipids. After preparation of the o-phthalaldehyde derivatives, the long-chain bases could be separated using C18 columns eluted isocratically with methanol:5 mM potassium phosphate, pH 7.0 (90:10). The HPLC analyses took 15 to 20 min per sample and had lower limits of detection in the picomole range. Quantitation was facilitated by using a 20-carbon long-chain base homolog as an internal standard. The utility of the method was demonstrated with rat liver, providing the first quantitation of free sphingosine in this tissue of approximately 7 nmol/g wet wt. 相似文献
2.
NIH/3T3 cells transfected with human tumor DNA containing activated ras oncogenes express the metastatic phenotype in nude mice. 总被引:20,自引:4,他引:16
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U P Thorgeirsson T Turpeenniemi-Hujanen J E Williams E H Westin C A Heilman J E Talmadge L A Liotta 《Molecular and cellular biology》1985,5(1):259-262
NIH/3T3 cells transfected with DNA from malignant human tumors produced experimental and spontaneous metastases in nude mice. In contrast, parent or spontaneously transformed NIH/3T3 cells failed to metastasize. The transfected clones contained either activated c-Harvey-ras or N-ras oncogenes. A representative clone (T71-17SA2) which was used to assess selected cellular and host factors relevant to the metastatic process produced lung metastases in 100% of the NIH nude mice recipients, secreted augmented levels of type IV collagenase, and invaded human amnion basement membrane in vitro. Expression of the metastatic phenotype was not related to decreased sensitivity to natural killer cells or macrophage-mediated cytotoxicity. Analysis of the cellular DNA from the T71-17SA2 transfectant and its corresponding metastases, both of which contained activated N-ras oncogenes, revealed a twofold increase in the N-ras-specific DNA sequences in the metastatic cells. Thus, transfection with human tumor DNA containing activated ras oncogenes can induce the complete metastatic phenotype in NIH/3T3 cells by a mechanism apparently unrelated to immune cell killing. 相似文献
3.
Purification and characterization of a murine basement membrane collagen-degrading enzyme secreted by metastatic tumor cells 总被引:13,自引:0,他引:13
A type IV collagen-degrading enzyme activity secreted by a highly metastatic mouse tumor was purified by concanavalin A- and type IV collagen-agarose affinity chromatographies followed by gel filtration on Bio-Gel A-0.5 m. The apparent molecular weight of the enzyme was 160,000 but about 70,000 when Triton X-100 was added to the column buffer. The purified enzyme protein was resolved on sodium dodecyl sulfate-polyacrylamide gel electrophoresis into two polypeptide chains of about 68,000 and 62,000 daltons. The enzyme activity could be increased by preincubation with trypsin and it is possible that the two chains represent latent and active enzyme forms. The enzyme activity was not reduced in the presence of dithiothreitol, it had a pH optimum of 7.6 and was inhibited by EDTA but not N-ethylmaleimide, phenylmethylsulfonyl fluoride, or Trasylol. The inhibition with EDTA was reversible. The pro-alpha 1(IV) and pro-alpha 2(IV) chains of the type IV procollagen substrate were both degraded at a similar rate to form two pairs of degradation fragments corresponding in molecular weights to about 70 and 30% of the original size chains. The presence of Triton X-100 increased slightly the activity of the enzyme and diminished the reduction of its activity upon freezing, indicating that the enzyme is a hydrophobic protein. 相似文献
4.
The elastin receptor shows structural and functional similarities to the 67-kDa tumor cell laminin receptor 总被引:10,自引:0,他引:10
R P Mecham A Hinek G L Griffin R M Senior L A Liotta 《The Journal of biological chemistry》1989,264(28):16652-16657
Laminin- and elastin-binding proteins were isolated by ligand affinity chromatography from plasma membranes of fetal bovine auricular chondroblasts and human A2058 melanoma cells. From both cell types, a 67-kDa protein was identified which bound to either elastin or laminin affinity resins. Structural and functional similarities between the elastin and laminin-binding proteins were suggested by 1) cross-reactivity between antibodies directed against the two proteins; 2) elution of the laminin receptor from laminin columns with soluble elastin peptides; and 3) modulation of substrate binding by galactoside sugars. In addition, extraction properties indicate that both receptors are peripheral membrane proteins whose association with the cell surface is mediated by their lectin properties. Mapping of the binding site on laminin suggests that the 67-kDa chondroblast receptor interacts with a hydrophobic elastin-like sequence in domain V of the B1 chain, and chemotaxis studies indicate that cell migration to elastin peptides and laminin involves the same receptor. 相似文献
5.
C W Slife E Wang R Hunter S Wang C Burgess D C Liotta A H Merrill 《The Journal of biological chemistry》1989,264(18):10371-10377
Long-chain (sphingoid) bases may serve as another category of "lipid second messenger" because they inhibit protein kinase C and affect multiple cellular functions. Free sphingosine has been found in rat liver (Merrill, A. H., Jr., Wang, E., Mullins, R. E., Jamison, W. C. L., Nimkar, S., and Liotta, D. C. (1988) Anal. Biochem. 171, 373-381); hence, this study determined if liver plasma membranes contain free long-chain bases and have the ability to form them from endogenous enzymes and substrates. Isolated plasma membranes contained 0.45 nmol of sphingosine/mg of protein which, based on the recovery of the membranes, was equivalent to 3.5 +/- 1.2 nmol/g of liver and at least half of the total free sphingosine in liver. When the membranes were incubated at 37 degrees C, the amount increased at an initial rate of 5-25 pmol/min/mg, resulting in a 2-3-fold increase over an hour. Sphingosine formation required divalent cations, was optimal at neutral to alkaline pH, and was temperature-dependent. Activities with these characteristics were not identified in microsomes or lysosomes (lysosomal activities with acidic pH optima were detected, however); hence, they appear to reflect a separate plasma membrane system. Sphingosine formation was stimulated by ceramides either added exogenously or formed endogenously by treating the membranes with sphingomyelinase (but not endoglycoceramidase). Sphingomyelin hydrolysis to ceramide was also observed during incubation of the plasma membranes alone. Some of the properties of this system resembled the neutral sphingomyelinase and ceramidase activities of liver. While the physiological significance of this endogenous sphingosine is not known, this system has the appropriate subcellular location to provide sphingosine as a participant in signal transduction. 相似文献
6.
Nielsen J; Peixoto AA; Piccin A; Costa R; Kyriacou CP; Chalmers D 《Molecular biology and evolution》1994,11(6):839-853
The region of the clock gene period (per) that encodes a repetitive tract
of threonine-glycine (Thr-Gly) pairs has been compared between Dipteran
species both within and outside the Drosophilidae. All the non-
Drosophilidae sequences in this region are short and present a remarkably
stable picture compared to the Drosophilidae, in which the region is much
larger and extremely variable, both in size and composition. The
accelerated evolution in the repetitive region of the Drosophilidae appears
to be mainly due to an expansion of two ancestral repeats, one encoding a
Thr-Gly dipeptide and the other a pentapeptide rich in serine, glycine, and
asparagine or threonine. In some drosophilids the expansion involves a
duplication of the pentapeptide sequence, but in Drosophila pseudoobscura
both the dipeptide and the pentapeptide repeats are present in larger
numbers. In the nondrosophilids, however, the pentapeptide sequence is
represented by one copy and the dipeptide by two copies. These observations
fulfill some of the predictions of recent theoretical models that have
simulated the evolution of repetitive sequences.
相似文献
7.
Evolutionary origin of human and primate malarias: evidence from the circumsporozoite protein gene 总被引:8,自引:1,他引:7
We have analyzed the conserved regions of the gene coding for the
circumsporozoite protein (CSP) in 12 species of Plasmodium, the malaria
parasite. The closest evolutionary relative of P. falciparum, the agent of
malignant human malaria, is P. reichenowi, a chimpanzee parasite. This is
consistent with the hypothesis that P. falciparum is an ancient human
parasite, associated with humans since the divergence of the hominids from
their closest hominoid relatives. Three other human Plasmodium species are
each genetically indistinguishable from species parasitic to nonhuman
primates; that is, for the DNA sequences included in our analysis, the
differences between species are not greater than the differences between
strains of the human species. The human P. malariae is indistinguishable
from P. brasilianum, and P. vivax is indistinguishable from P. simium; P.
brasilianum and P. simium are parasitic to New World monkeys. The human P.
vivax-like is indistinguishable from P. simiovale, a parasite of Old World
macaques. We conjecture that P. malariae, P. vivax, and P. vivax-like are
evolutionarily recent human parasites, the first two at least acquired only
within the last several thousand years, and perhaps within the last few
hundred years, after the expansion of human populations in South America
following the European colonizations. We estimate the rate of evolution of
the conserved regions of the CSP gene as 2.46 x 10(-9) per site per year.
The divergence between the P. falciparum and P. reichenowi lineages is
accordingly dated 8.9 Myr ago. The divergence between the three lineages
leading to the human parasites is very ancient, about 100 Myr old between
P. malariae and P. vivax (and P. vivax-like) and about 165 Myr old between
P. falciparum and the other two.
相似文献
8.
Photosynthetic enhancement studies performed at 619 nm (excitation of Systems I and II) and at 446 nm (mainly excitation of System I) revealed an 18% photosynthetic enhancement simultaneously with a 31% reduction in glycolate excretion. This observation supports the hypothesis that some glycolate may be consumed in an oxidation process associated with System I when System II is poorly excited and the supply of electrons from the water splitting process of photosynthesis is low. 相似文献
9.
Comparative metabolic clearance rates of beta-endorphin and beta-lipotropin in humans 总被引:1,自引:0,他引:1
In normal human subjects under basal conditions, we have reported that molar concentrations of immunoreactive β-lipotropin (IR-β-LPH) are approximately threefold greater than those of IR-β-endorphin (β-Ep). Following acute stimulation, there is a further two- to threefold disproportionate rise in plasma concentrations of IR-β-LPH as compared to those of IR-β-Ep. To begin to assess the possible factors involved in such altered IR-β-LPH/IR-β-Ep ratios in plasma, the metabolic clearance rate (MCR), volume of distribution (Vd), fractional rate of disappearance (Kd), and half-life () of these peptides were determined by means of bolus injection of highly purified human β-LPH and synthetic human β-Ep in normal human subjects. β-Ep was found to have an MCR and a Kd greater than that of β-LPH, and a shorter . These differences, however, although they may in part be contributory, cannot solely account for the greater ratio of IR-β-LPH to IR-β-Ep in plasma, or for the disproportionate rise in plasma concentrations of these peptides after acute stimulation. 相似文献
10.
Marina Giuliano Mauro Andreotti Giuseppe Liotta Haswell Jere Jean-Baptiste Sagno Martin Maulidi Sandro Mancinelli Ersilia Buonomo Paola Scarcella Maria F. Pirillo Roberta Amici Susanna Ceffa Stefano Vella Leonardo Palombi Maria Cristina Marazzi 《PloS one》2013,8(7)