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141.
The action of the tumor promoter, phorbol 12,13-dibutyrate (PDBu), on rabbit peritoneal and human neutrophils is associated
with stimulation of14C-arachidonic acid incorporation into phospholipids within 1–2 min. Stimulated14C-arachidonate incorporation was relatively selective for phosphatidylinositol (PI) in rabbit neutrophils. In contrast, the
secretory response of human neutrophils to PDBu coincided with stimulated label incorporation into phosphatidylserine (PS),
phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidic acid (PA) and PI. Significant increases in label incorporation
were observed with PDBu concentrations as low as 2 nM, and the dose response of stimulated label incorporation paralleled
that of evoked lysozyme secretion. A parallel, but partial, inhibition of PDBu-stimulated PI labeling and enzyme release was
observed after exposing rabbit neutrophils to calcium-deprived medium, whereas calcium deprivation failed to significantly
depress either of these stimulant actions of PDBu in human neutrophils. Further, in rabbit neutrophils PDBu elicited an increase
in cell associated45Ca. However, PDBu was unable to promote the incorporation of32P orthophosphate into PI or enhance phospholipase A2 activity in broken cells. These findings suggest that one expression of the interaction between phorbol esters and their
receptors on neutrophils involves the turnover of arachidonic acid in phospholipids. This stimulated turnover of arachidonate
may be a critical step in the cascade of events associated with neutrophil activation. 相似文献
142.
143.
144.
Bracken,Pteridium aquilinum, exerts a strong dominance over associated plants throughout much of its worldwide range. Associated plants are often severely inhibited or even excluded from dense stands of the fern. This study investigated the various aspects of herb suppression in bracken stands and assessed the contribution of the various forms of interference between plants to the establishment and maintenance of bracken dominance. It was shown that competition for soil moisture, light, and nutrients could not account for the lack of herbs in bracken stands. Further, uniformity of soil pH, texture, water-holding capacity, and organic matter content ruled out variability in physical factors as a cause. Baiting and trapping experiments showed that the higher concentration of animal activity inside the bracken stands contributed significantly to the pattern of herb suppression, but only against select species. The maintenance of this pattern in the animal-free Santa Cruz Island stands indicates the importance of another factor, allelopathy. It was found that phytotoxins leached from the dead, standing bracken fronds with the first few rains of the wet season were largely responsible for herb suppression. These toxins were isolated in raindrip and from soil inside the fern stands. Removal of the fronds from the stand before the rains could leach them resulted in reinvasion by the herbs after several seasons, and, conversely, placing fronds over the herbs in the grassland brought about herb inhibition. A number of known allelopathic chemicals were tentatively identified from bracken leachates. The importance of the interaction of allelopathy with other factors of plant interference is illustrated by bracken. 相似文献
145.
The thermal regeneration of activated carbons loaded with p-nitrophenol (PNP) and other aromatic compounds was studied using a thermal balance. After pyrolysis of the adsorbates in nitrogen at 700°C, the residues were gasified with oxygen at 415 to 500°C or with steam at 840 to 920°C. Residues from PNP were several times more reactive to oxygen than the base carbons and also showed greater chemisorption of oxygen. For steam gasification, only small differences between spent and fresh carbons were found. 相似文献
146.
现代科学技术,尤其是生物技术和计算机技术的飞速发展和广泛应用,给化妆品行业带来了全新的发展机遇,赋予化妆品以一定的功效性是新世纪化妆品发展的重要趋势.近20年来,人们对化妆品的要求已从洁肤、润肤为目的的基础护肤品向美白、祛皱为目的的功效性化妆品方向发展. 相似文献
147.
A colorimetric determination of fatty acids as a new assay of lipases in reverse micelles 总被引:3,自引:0,他引:3
Peter Walde 《Journal of the American Oil Chemists' Society》1990,67(2):110-115
A new simple spectrophotometric method is described for the determination of the free fatty acid content in triglyceride oils
or other lipophilic samples. The method utilizes phenol red as fatty acid indicator, which is solubilized phenol red as fatty
acid indicator, which is solubilized in reverse micelles formed by AOT [sodiumbis(2-ethylhexyl) sulfosuccinate] in isooctane. Fatty acid determinations in vegetable oils can be carried out rapidly with oil
samples of less than 100 mg. The acid value of three different oils tested agreed quite well with the acid value obtained
for the same samples with another colorimetric determination using cupric acetate.
The method can be extended to a continuous determination of fatty acids which are released during the initial stage of a lipase
catalyzed hydrolysis of triglyceride substrates in reverse micelles. This new sensitive lipase assay has been applied for
a lipase ofPseudomonas bacteria with lipase concentrations as low as 0.1 μg/ml. Using trioctanoylglycerol as substrate in 50 mM AOT/isooctane with
wo=[H2O]/[AOT]=11.1 (pH 9.0), the apparent overall Michaelis-Menten constant (Km′app,ov) is 27 mM and the turnover number (kcat) 44 sec−1. 相似文献
148.
The subliquidus miscibility gap in the system K2 O-B2 O3 -SiO2 has been determined for compositions with molar ratios SiO2 /B2 O3 <2 and T≥550°C. The shape of the miscibility gap is an elongated dome similar in form to, but less extensive than those in the lithium and sodium borosilicate systems. The consolute composition (molar) and temperature are estimated to be 4 ± 1 K2 O -30±8 B2 O3 -66±8 SiO2 and 629±5°C, respectively . 相似文献
149.
Cloud computing is an elastic computing model where users can lease computing and storage resources on demand from a remote infrastructure.It is gaining popularity due to its low cost,high reliability,... 相似文献
150.
Dr. H. K. Verma 《Acta Mechanica》1966,2(4):392-397
Summary The mixed boundary-values problem of elasticity with parabolic boundary when the prescribed displacement is parabolic has been reduced to the solution of the non-homogeneous Hilbert problem following the method of complex variable. The result has been compared with that obtained byParia [5] for parabolic boundary with prescribed constant displacement as a particular case.
Zusammenfassung Das gemischte Randwertproblem der Elastizitätstheorie wird für parabolische Berandung auf die Lösung des inhomogenen Hilbert-Problems unter Benützung der komplexen Methode zurückgeführt. Die Randverschiebung wird durch ein Polynom zweiten Grades dargestellt. Das Ergebnis wird mit dem vonParia [5] verglichen, das als Sonderfall konstante Verschiebungen am parabolischen Rand vorschreibt.相似文献