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61.
In 1974, Zimm described a theory which predicts that the sedimentation coefficient of high-molecular-weight DNA will decrease as the rotor speed of measurement increases. In 1979, this theory was revised, and the new formula predicts speed-dependence effects that are substantially smaller than the predictions of the original version. This report describes the results of subjecting both the original and the revised versions of the theory to quantitative tests using a well-defined sucrose-gradient system and a DNA of known molecular weight (T4c DNA). T4c bacteriophage is a mutant, whose DNA contains the unmodified base cytosine, instead of the glucosylated hydroxymethylcytosine characteristic of the T-even bacteriophages, and has a molecular weight of 115 ± 3 × 106. The DNA of the wild-type phage (T4D+) was also used in some experiments. In addition to the quantitative tests, the experiments test for an effect first observed by Rubenstein and Leighton, which showed that the sedimentation coefficient measured for T2 DNA depended on the composition of the centrifuge tube used for the measurement (tube composition effect). It can be inferred from this observation that an interaction occurs between particle and tube wall during sedimentation, and this leads to a reduction in sedimentation velocity independent of the reduction in S described by Zimm's theory. The results show that in the range of 25,000–50,000 rpm, the original but theoretically incorrect form of the theory quite accurately describes the sedimentation behavior of both T4c and T4D+ DNA, although T4D+ was a special case in some respects. The revised (corrected) form of the theory predicts much less of a speed-dependence effect than that actually observed. The discrepancy between corrected theory and observation suggests that other factors (perhaps arising from the use of the swinging bucket rotor geometry) are causing the additional observed reduction in S20,w. However, the experiments show that the tube composition effect does not seem to be one of these. 相似文献
62.
Roger Schallreuter 《Pal?ontologische Zeitschrift》1979,53(1-2):129-135
From Upper Ordovician Öjlemyrflint erratic boulders of the Kaolinsand (Plio-/Pleistocene) of the Isle of Sylt (North Sea) a problematical microfossil is described which possibly represents an ontogenetical stage of a bilateral-symmetrical animal (? trilobite). 相似文献
63.
Roger L. Crumley 《The Western journal of medicine》1977,126(3):184-189
Treatment techniques for airway obstruction in croup and epiglottitis are reviewed in the medical literature. Series totaling 295 nasotracheal intubations, and 591 tracheostomies were reviewed. There were two deaths attributable to airway complications in 126 patients in whom nasotracheal intubation was carried out. In three patients subglottic granulation tissue and subglottic stenoses developed from short-term nasotracheal intubation. There were no subglottic stenoses or tracheal stenoses reported in the 591 tracheostomies. From this review, it would seem feasible to use nasotracheal intubation for short-term airway treatment in croup and epiglottitis. The increasing occurrence of laryngeal and tracheal complications with long-term intubation suggests that tracheostomy be considered in such cases. 相似文献
64.
Brian Greenway M J Iqbal P J Johnson Roger Williams 《BMJ (Clinical research ed.)》1983,286(6359):93-95
The detection of high activities of two sex-steroid biosynthetic enzymes—aromatase and 5-alpha-reductase—in pancreatic carcinoma tissue suggested the possibility that these enzymes may influence the circulating concentrations of sex-steroid hormones. Mean serum testosterone concentrations in 22 men and women with exocrine carcinoma of the pancreas were significantly lower than those in 20 healthy controls and 27 patients with other known malignancies, who were of similar age and sex composition. Low serum testosterone concentrations may be due to uptake by and metabolism within the tumour; alternatively, patients with low androgen concentrations may be at greater risk of developing pancreatic carcinoma. 相似文献
65.
The purpose of this study was to learn wether a number of Ca2+ antagonists were effective in reducing contractile response of the isolated ileum of the sensitized and normal guinea pig. Contractions of the normal ileum in response to LTD4, acetylcholine, histamine, and potassium chloride were obtained before and after verapamil, diltiazen and papaverine. Ovalbumin-induced contractions of the ovalbumin-sensitized ileum were obtained in the presence of the three Ca2+ antagonists. In the normal ileum, all the Ca2+ antagonists were highly effective in diminishing the contractile responses to LTD4, acetylcholine, histamine and potassium chloride. In the sensitized ileum, ovalbumin-evoked contractions, with subsequent release of a potent contractile mediator (presumably SRS-A), were Ca2+-dependent since verapamil, diltiazem and papaverine caused a concentration-related reduction of contractions. Thus, the influx of extracellular Ca2+ plays a key role in the contractile responses of the normal and sensitized guinea pig ileum when stimulated by various potent agonists acting on specific receptors or on the cell membrane. 相似文献
66.
We have previously shown that several agents which interfere with binding of ligands to the mannose-glycoprotein receptor on macrophages can inhibit zymosan-induced lysosomal enzyme secretion. Here we show that mannose only reduces the association of zymosan with macrophages during the first hour of exposure; after longer periods of uptake no effect is detectable. We have previously shown that mannose reduces surface binding of zymosan, probably by interfering selectively with binding to the mannose receptor. The present inhibition of association of zymosan with macrophages during short exposures can be entirely explained by this reduction of binding. Macrophages must therefore internalize zymosan at sites in addition to the mannose receptor. In contrast to macrophages the murine macrophage-like cell line P388D1 is lacking the mannose-glycoprotein receptor. Accordingly we find that binding of zymosan to P388D1 is much slighter than to macrophages and is unaffected by mannose or mannose-6-phosphate. The spontaneous lysosomal enzyme secretion of P388D1 is also unaffected by mannose. The data on macrophages confirm our previous suggestion that agents interfering with the mannose receptor inhibit the induction of lysosomal enzyme secretion by acting directly on the receptor. The data on P388D1 cells support this assertion by excluding effects at later steps in the secretory pathway. 相似文献
67.
W. A. Schroeder Darleen Powars Joan B. Shelton J. Roger Shelton J. B. Wilson T. H. J. Huisman Antranik A. Bedros 《Biochemical genetics》1982,20(11-12):1175-1187
After a boy of Mexican-American descent became jaundiced during treatment of a serious urinary tract infection with an oxidant drug, an extensive hematological examination was made. The important finding was the presence of Hb-Leiden to the extent of less than 3% or about a tenth of the usual percentage. Although inclusion bodies are present in the erythrocytes at all times, his hematological parameters have remained normal. The genetic basis for the unusually small amount of Hb-Leiden in the propositus may be due to the Hb-Leiden gene in an anti-Lepore configuration, that is, and Hb-Leiden gene in cis to the normal β and δ genes. 相似文献
68.
Roger Wigren Hans Elwing Ragnar Erlandsson Stefan Welin Ingemar Lundstrm 《FEBS letters》1991,280(2):225-228
It is shown that scanning force microscopy (SFM), operated in the attractive mode, can be used to obtain high resolution pictures of adsorbed fibrinogen molecules on solid surfaces, without the need for staining or special microscope grids. SFM also reveals the three-dimensional structure of the adsorbed molecules. Two forms of adsorbed fibrinogen are demonstrated on hydrophobic silicone dioxide surfaces; a trinodular about 60 nm long and a globular with about a 40 nm diameter. Polymeric networks formed after storage of the surface with adsorbed fibrinogen in PBS for 11 days are also shown. The SFM-results for the trinodular structure suggest the existence of loops or peptide chains extending outside the basic structure of the fibrinogen molecule. 相似文献
69.
70.
ORSTOM-IRRI collaborative program on nitrogen fixation 相似文献