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61.
Characterization and Stability of Ribosomes from Mesophilic and Thermophilic Bacteria 总被引:4,自引:1,他引:3 下载免费PDF全文
Ribosomes were isolated from three mesophilic and three thermophilic strains of Bacillus. The ribosomes consisted of about 55% protein and 45% ribonucleic acid. Average ratios for the absorbance at 260/235 and 260/280 mmu were 1.77 and 1.92 for the mesophiles and 1.63 and 1.84 for the thermophiles. Ultracentrifugation revealed mainly components with sedimentation coefficients of about 30, 50, 70, 100, and 120S. All the preparations were shown to contain a ribonuclease which, in the presence of ethylenediaminetetraacetic acid, led to ribosome breakdown as measured by the increase in acid-soluble nucleotides. The stability of the ribosomes from the thermophiles was consistently greater than that of the ribosomes from the mesophiles. After 5 hr at 37 C, the breakdown was about 80% for the ribosomes from the mesophiles and 55 to 70% for those from the thermophiles. At 60 C, the ribosomes from the mesophiles were broken down slightly more and at a faster rate than those from the thermophiles. At temperatures above 60 C, the breakdown was again more pronounced for the ribosomes from the mesophiles. 相似文献
62.
63.
绕茧蜂属Ropalophorus Curtis,1837是茧蜂科中的一个小属,迄今世界上仅记载有2种。一种为R.clavicornis(Wesmael),1835,分布于欧州及日本,寄生于云杉八齿小蠹Ips typographus及I.amitinus成虫体内;另一种为R.wisconsinensis Shenefelt,1960,仅分布于美国,由于该种是用诱捕器捕到的,因此,其奇主不详,但有可能为I.pini(Shenefelt,1960)。 相似文献
64.
Lumenal hydrolysis of menhaden and rapeseed oils and their fatty acid methyl and ethyl esters in the rat 总被引:4,自引:0,他引:4
Simple alkyl (ethyl) esters of polyunsaturated fish oil fatty acids have been proposed as dietary supplements, but their relative efficiency of digestion and absorption have not been determined. Using stomach tubes, we gave rats menhaden or rapeseed oils, or the corresponding methyl and ethyl esters, and determined by chromatographic methods the lipid classes and molecular species recovered from the lumen of the jejunum during the first 1 to 2.5 h of digestion. Hydrolysis of menhaden oil resulted in a preferential retention of a high proportion of the polyunsaturated long chain acids in the sn-2-monoacylglycerols and in the residual triacyglycerols, while digestion of rapeseed oil led to a preferential release of free long chain monounsaturated fatty acids. In contrast, hydrolysis of the alkyl (methyl and ethyl) esters of the fatty acids of either menhaden or rapeseed oil resulted in a composition of free fatty acids which was much more representative of the original esters. It was therefore concluded that the differential lumenal liberation of the long chain and polyunsaturated (three or more double bonds) fatty acids from fish and rapeseed oil is largely due to their characteristic distribution between the primary and secondary positions in the glycerol molecule, and to a much lesser extent to a chain length discrimination by pancreatic lipase. This study also shows that the methyl and ethyl esters are hydrolyzed about 4 times more slowly than the corresponding triacylglycerols, which is sufficient to maintain a saturated micellar solution of fatty acids in the intestinal lumen during absorption. 相似文献
65.
The fetal rat binding protein for insulin-like growth factors is expressed in the choroid plexus and cerebrospinal fluid of adult rats 总被引:2,自引:0,他引:2
L Y Tseng A L Brown Y W Yang J A Romanus C C Orlowski T Taylor M M Rechler 《Molecular endocrinology (Baltimore, Md.)》1989,3(10):1559-1568
The biological effects of the insulin-like growth factors, IGF-I and IGF-II, on their receptors are modulated by IGF-binding proteins. Recently, we isolated a cDNA clone for one member of the family of IGF-binding proteins, BP-3A, a 30 kilodalton (kDa) protein synthesized by the BRL-3A rat liver cell line. BP-3A is related to but distinct from two other cloned IGF-binding proteins, the human amniotic fluid binding protein and the glycosylated binding subunit of the 150 kDa IGF-binding protein complex in serum. It is expressed in multiple nonneural tissues and in serum in the fetal rat and decreases after birth, similar to the developmental pattern of IGF-II expression. IGF-I, IGF-II, and their receptors are expressed in brain. The present study examines the expression of BP-3A in the rat central nervous system. By Northern blot analysis, BP-3A mRNA is present at high levels in brain stem, cerebral cortex, and hypothalamus from 21-day gestation rats and, like IGF-II mRNA, persists in adult rat brain. The site of BP-3A mRNA synthesis was localized by in situ hybridization to coronal sections of adult rat brain using 35S-labeled oligonucleotides, 48 bases in length, complementary and anticomplementary to the coding region of BP-3A. Specific hybridization of the BP-3A probe was observed exclusively to the choroid plexus extending from the level of the medial preoptic nucleus to the arcuate nucleus of the hypothalamus, similar to the previously reported preferential localization of IGF-II mRNA to the choroid plexus. Synthesis of BP-3A mRNA by choroid plexus suggested that BP-3A might be secreted into the cerebrospinal fluid. A 30 kDa IGF-binding protein was demonstrated in rat cerebrospinal fluid that is recognized by antibodies to BP-3A and, like purified BP-3A, has equal affinity for IGF-I and IGF-II. By analogy with other transport proteins synthesized by the choroid plexus, BP-3A may facilitate the secretion of IGF-II to the cerebrospinal fluid and modulate its biological actions at distant sites within the brain. 相似文献
66.
Enantiomers of diastereomeric benzo[a]pyrene (BP) diol-epoxides, r-7,t-8-dihydroxy-t-9,10-epoxy-7,8,9,10-tetrahydro-BP (BP 7,8-diol-anti-9,10-epoxide), r-7,t-8-dihydroxy-c-9,10-epoxy-7,8,9,10-tetrahydro-BP (BP 7,8-diol-syn-9,10-epoxide), r-9,t-10-dihydroxy-t-7,8-epoxy-7,8,9,10-tetrahydro-BP (BP 9,10-diol-anti-7,8-epoxide), and several 7,8,9,10-tetrahydroxy-7,8,9,10-tetrahydrobenzo[a]pyrenes (BP tetrols) were resolved by high-performance liquid chromatography (HPLC) using columns packed with either (R)-N-(3,5-dinitrobenzoyl)phenylglycine[(R)-DNBPG] or (S)-N-(3,5-dinitrobenzoyl)leucine [(S)-DNBL], which is either ionically or covalently bonded to gamma-aminopropylsilanized silica. Resolution of enantiomers was confirmed by ultraviolet-visible absorption and circular dichroism spectral analyses. Resolved enantiomers of BP diol-epoxides were each hydrolyzed in acidic solution to a pair of diastereomeric tetrols which were separated by reversed-phase HPLC. Absolute stereochemistries of enantiomeric diol-epoxides were deduced by the absolute configuration of their hydrolysis products. 相似文献
67.
68.
The objectives of the present study were: 1) to develop a simple and more efficient technique for sperm microinjection than is currently available, using the rabbit as a model, and 2) to evaluate the development of rabbit oocytes fertilized by single or multiple sperm microinjection. Hyperosmotic sucrose in phosphate-buffered saline (SPBS) was employed to dehydrate oocytes to increase the perivitelline space for sperm microinjection and prevent possible injury to the vitellus. In the first experiment, 58% (n = 29) oocytes treated with 0.5 M SPBS developed to morulae following multiple sperm microinjection compared, respectively, to 47% (n = 34) and 60% (n = 15) for control IVF with or without sucrose exposure (P greater than 0.05). Blastocyst development from microinjected oocytes, however, was much lower (P less than 0.05) than that of controls (14% vs. 42% and 40%, respectively). Sham operation by puncturing the zona pellucida of the sucrose-treated oocytes with the microinjection pipette did not increase parthenogenesis (P greater than 0.05). In Experiment 2 a smaller-size injection pipette and shorter sucrose exposure time after sperm microinjection resulted in 41% (n = 42) of the oocytes developing into blastocysts for the microinjection group, whereas only 21% (n = 24) developed to blastocysts in the control IVF group (P less than 0.05). When relatively older oocytes (17 hr post ovulation injection) were used to test if microinjection could reduce the time to fertilization and cleavage (Expt. 3), an average of 27% (n = 63) blastocysts resulted from microinjection vs. 0% (n = 28) for the control IVF group. 相似文献
69.
Dissociated embryonic chick dorsal root ganglion (DRG) neurons maintained in culture exhibit a mixed Na+/Ca2+ action potential. The characteristic "shoulder" on the repolarizing phase is due to the relatively prolonged inward Ca2+ current. DRG neurons grown in an elevated K+ medium (25 versus. 5 mM) lack the plateau phase of the action potential. Voltage-clamp analysis showed that this plastic change in action potential duration is not due to the loss of the inward Ca2+ current but is partly due to the appearance of a Ca2(+)-dependent, 4-aminopyridine-(4-AP)-sensitive transient outward current. Faster activation of the purely voltage-dependent delayed rectifier outward current also contributes to the rapid repolarization observed in neurons cultured in elevated K+ medium. 相似文献
70.
Long-chain unsaturated fatty acids (UFA) having up to six double bonds are derivatized to 2-substituted 4,4-dimethyloxazolines (DMOX) and then analyzed by combined in-beam electron impact (IBEI)-B/E-linked scan mass spectrometry. This technique provides highly characteristic mass spectra and may serve as an auxiliary means for direct structure determination of individual UFA in mixtures. 相似文献