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61.
Acid sphingomyelinase was purified to homogeneity from human placenta in the presence of a dialyzable detergent, n-octyl-beta-D-glucopyranoside. The major steps in the procedure included column chromatographies with Con A-Sepharose, sphingosylphosphorylcholine-Sepharose 4B, hexyl-agarose, and Mono P. The purified enzyme with pI 7.4 had a specific activity of approx 170,000 units/mg protein with a yield of 3.6%. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed a single protein band of Mr 62,000. Gel filtration with a Superose 12 column gave a single peak, and the enzyme in the presence 50 mM n-octyl-beta-D-glucopyranoside was of Mr 123,000, indicating that the native enzyme occurs in a dimeric form. The optimal pH was 5.5 with both sphingomyelin and an artificial substrate, 2-N-hexadecanoylamino-4-nitrophenylphosphorylcholine. The Km values were 55 microM with sphingomyelin and 340 microM with the artificial substrate. The enzyme activity was not affected by Mg2+ (1-5 mM), confirming that the enzyme is acid sphingomyelinase. The enzyme was stable at -80 degrees C for more than 4 months. In addition to the enzyme with pI 7.4, the Mono P chromatofocusing gave two peaks (pI 7.0 and 6.7) possessing the enzymatic activity. 相似文献
62.
本文共记述盲蝽科叶盲蝽亚科(Phylinae)新种两个,计为:宽束盲蝽 Pilophorus latus sp.nov.和黄平盲蝽 Zanchius vitellinus sp.nov.。两新种的模式产地均为云南。并记录了6个中国新纪录种,计为:棕二带束盲蝽 Pilophorus alstoni Schuh、长黑束盲蝽 Pilophorus dailahn Schuh、细毛束盲蝽 Pilophorus setulosus Horvath、朝束盲蝽 Pilophorus koreanus Josifov、褐束盲蝽 Pilophorusgallicus Remane、亮束盲椿 Pilophorus lucidus Linnavuori。 相似文献
63.
64.
We have identified two estradiol-dependent single-stranded DNA binding proteins in the nucleus and cytoplasm of chicken hepatocytes that bind the sequence 5'TCACCTTCGCTATG3' in the first exon of the chicken vitellogenin gene. As judged by chromatography on heparin-Sepharose and by proteolytic clipping bandshift assay, the two proteins are different. Furthermore, they only bind to the oligonucleotide corresponding to the upper strand. Depurination and depyrimidination interference experiments with the cytoplasmic protein show that the bases CCTT-G are involved in the protein-DNA interaction. An RNA corresponding to the upper strand of the gene between nucleotide positions -73 and +53 competes for binding to the single-stranded DNA. UV cross-linking experiments performed with bromouridine-substituted single-stranded RNA reveal that an estradiol-dependent hepatocyte cytoplasmic protein with a Mr of 71,000 binds to the mRNA-like single-stranded RNA. 相似文献
65.
Cholera toxin as a mucosal adjuvant. Glutaraldehyde treatment dissociates adjuvanticity from toxicity 总被引:3,自引:0,他引:3
Cholera toxin (CT), either mixed with or conjugated to unrelated protein Ag, is known to enhance the intestinal IgA response of rodents toward the unrelated Ag. Although relatively low doses of CT exert this gut mucosal adjuvant effect, the inherent toxicity of CT is a hindrance to its use in humans. Our report demonstrates that CT treated with 20 mM glutaraldehyde retains adjuvant properties but exhibits more than 1000-fold lower toxicity than untreated toxin. Glutaraldehyde was also used in a one-stage conjugation procedure to couple CT covalently to Sendai virus. Again, toxicity was reduced more than 1000-fold. This drop in toxicity is consistent with an observed 100-fold loss in binding capacity of the CT B subunit and a 20- to 50-fold reduction in adenylate cyclase activation by the CT A subunit. Oral administration of this virus-toxoid conjugate resulted in increased gut antiviral IgA titers compared with oral administration of either virus alone or of virus mixed with glutaraldehyde-treated toxin. This marked decrease in toxicity may afford a practical approach for the use of CT as a mucosal adjuvant. 相似文献
66.
钐在小鼠肝脏细胞中的动态观察 总被引:8,自引:0,他引:8
It is generally considered that the rare earth compounds are plasma membrane-impermeable, thus affecting the cells only on their surface. Recently, we found that after repeated injections to mice of large dose of samarium trichloride, a soluble compound of rare earth, samarium aggregates appeared in Kupffer cells and hepatocytes of liver. In this study, we aimed at observing the route by which samarium enters the liver cells and the process of the formation of samarium aggregates. Samarium trichloride was given to Swiss mice at one dose of 70 mg/kg intravenously. Thereafter, at different intervals from 15 min to 48 h after the injection, the samarium in liver was traced dynamically by electron microscopy and X ray microanalysis. From 15 min to 2 h both Kupffer cells and hepatocytes endocytosed samarium-containing particles and formed phagosomes, in which the ingested particles were progressively concentrated. Besides, the small phagosomes fused with each other. Phagocytosis was especially active in Kupffer cells. During the 4 h to 24 h many Kupffer cells were degenerated and broken. In hepatocytes the phagosomes gathered mostly around the bile canaliculi. Groups of highly electron-dense particles were found in the lumen of bile canaliculi, implying the excretion of samarium by bile. At the 48 h, the samarium-containing phagosomies were found still in both kinds of cells in the liver. 相似文献
67.
68.
P C Babbitt G L Kenyon B M Martin H Charest M Slyvestre J D Scholten K H Chang P H Liang D Dunaway-Mariano 《Biochemistry》1992,31(24):5594-5604
We have deduced the nucleotide sequence of the genes encoding the three components of 4-chlorobenzoate (4-CBA) dehalogenase from Pseudomonas sp. CBS-3 and examined the origin of these proteins by homology analysis. Open reading frame 1 (ORF1) encodes a 30-kDa 4-CBA-coenzyme A dehalogenase related to enoyl-coenzyme A hydratases functioning in fatty acid beta-oxidation. ORF2 encodes a 57-kDa protein which activates 4-CBA by acyl adenylation/thioesterification. This 4-CBA:coenzyme A ligase shares significant sequence similarity with a large group of proteins, many of which catalyze similar chemistry in beta-oxidation pathways or in siderophore and antibiotic synthetic pathways. These proteins have in common a short stretch of sequence, (T,S)(S,G)G(T,S)(T,E)G(L,X)PK(G,-), which is particularly highly conserved and which may represent an important new class of "signature" sequence. We were unable to find any proteins homologous in sequence to the 16-kDa 4-hydroxybenzoate-coenzyme A thioesterase encoded by ORF3. Analysis of the chemistry and function of the proteins found to be structurally related to the 4-CBA:coenzyme A ligase and the 4-CBA-coenzyme A dehalogenase supports the proposal that they evolved from a beta-oxidation pathway. 相似文献
69.
Comparisons of the site specific binding of nitrobenzylthioinosine (NBMPR) to intact and lysed red cells from various mammalian and avian species suggest the presence of a cytoplasmic pool of nucleoside transporters. In some species the cytoplasmic pool is about 50% of the total (mouse). On the average, the cytoplasmic pool is approx. 20% of the surface pool of NBMPR-binding sites. In sheep reticulocytes, both pools disappear in an energy-dependent manner during the maturation of the reticulocyte in vitro. 相似文献
70.
Age-specific mortality rates were studied at two adult density levels in four inbred lines of Drosophila melanogaster. In experimental populations, adult densities were maintained at constant levels throughout the experiment by replacing dead flies with live, marked mutants. In control populations, densities declined naturally as the cohorts aged. For all experimental populations the best mortality model is the two-stage Gompertz model, with slower mortality acceleration at older ages. Flies in the experimental populations generally lived longer than flies in control populations, regardless of sex, genotype, or initial density level. The data demonstrate that deceleration of age-specific mortality rates at older ages is not caused by declining cohort densities. Mortality deceleration is a real phenomenon that raises serious questions about the evolution of senescence. 相似文献