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81.
Alistair L. Wilkins 《Phytochemistry》1977,16(12):2031-2032
The triterpenoids durvilldiol and durvillonol, isolated in earlier studies from the lichen Pseudocyphellaria berberina, syn. P. durvillei, are identified as stictane-3β,22α-diol and 22α-hydroxystictan-3-one respectively. 相似文献
82.
A method is described for the isolation of a homogeneous preparation of dense granules from procine platelets. The purified dense granule fraction contained approximately 400 nmol of 5-hydroxytryptamine/mg of protein and appeared to be homogeneous when examined by electron microscopy. Isolated dense granules transport exogenously added 5-hydroxytryptamine via two mechanisms: 1) a carrier-mediated process predominating at low substrate concentrations and 2) a diffusion-controlled process predominating at high substrate concentrations. Temperature studies revealed an apparent energy of activation of 14.9 kcal/mol for the carrier-mediated transport. Kinetic data yielded a Km of 3.3 micron and a Vmax of 0.79 nmol/min/mg of protein for the mediated transport process. Steady state uptake was sensitive to changes in medium osmotic pressure and a decline in uptake below 300 mosM was correlated with release of endogenous 5-hydroxytryptamine. The transport was inhibited by a number of structural analogs of 5-hydroxytryptamine. These results demonstrate the existence of a carrier-mediated transport system for 5-hydroxytryptamine in the membranes of the platelet dense granules. 相似文献
83.
Agneta Oskarsson Katherine S. Squibb Bruce A. Fowler 《Biochemical and biophysical research communications》1982,104(1):290-298
Gel chromatography of kidney postmitochondrial fractions from control rats 2 hr after injection of 203Pb or after in vitro incubation with 203Pb disclosed the presence of two fractionated Pb-binding components plus binding in the void volume and total volume regions. The binding of Pb to the two components, with molecular weights of 11,500 and 63,000 daltons, was markedly decreased in Pb-pretreated rats. Sodium dodecyl sulfate-gel electrophoresis and autoradiography showed the presence of one major 203Pb band with an estimated molecular weight of 60,000 daltons. The 11,500-dalton peak did not incorporate 14C-leucine nor did concomitant administration of cycloheximide with the 203Pb inhibit incorporation of 203Pb activity, suggesting that the component is a preformed constituent of the kidney. In vitro incubation of brain, liver and lung postmitochondrial supernatants with 203Pb disclosed that these two binding components were also present in brain but not in liver or lung, suggesting a target tissue-specific localization for these Pb-binding macromolecules. 相似文献
84.
85.
A J Molenaar S R Davis R J Wilkins 《The journal of histochemistry and cytochemistry》1992,40(5):611-618
We used 35S-labeled cRNA probes to localize the sites of alpha-lactalbumin, alpha-S1-casein, and lactoferrin mRNA synthesis in sheep and forcibly weaned cattle mammary tissue. Expression of alpha-lactalbumin was absent in three of four "virgin" glands studied, present in some alveoli of "pregnant" glands but not in others, despite a similar histological appearance. In the early lactating gland, expression was high in those alveoli with few fat globules in their cells and lumen and was absent in alveoli with abundant fat globules. These observations suggest either that alpha-lactalbumin gene expression is linked to the long-term secretory activity of cells and falls once cells are resting or regressing, or that there are cyclical variations in expression, or that in the lactating gland some groups of epithelial cells are synthesizing alpha-lactalbumin and some are synthesizing fat. Expression patterns of alpha-S1-casein were similar to those of alpha-lactalbumin. Lactoferrin, in contrast, was expressed almost exclusively in the "fatty alveoli" of both species. Our results show that dramatic variations in milk gene expression can occur throughout the mammary gland of sheep and cattle and that at no stage of pregnancy, lactation, or involution can the gland be considered metabolically homogeneous. 相似文献
86.
87.
Peter O. Wilkins 《Archives of microbiology》1982,132(2):211-215
A shift in the growth temperature of Streptococcus faecalis from 37 to 10°C resulted in an 18% increase in the proportion of unsaturated fatty acids. Electron spin resonance spectra of spin-labeled membranes and extracted phospholipids indicated viscosity changes consistent with the alterations in fatty acid composition. Growth temperature had no significant effect on the active transport of leucine and alanine; uptake rates assayed at 10 or 35°C were essentially the same in cells grown at either 10 or 37°C. The relative rapidity of amino acid transport, which presumably contributes to the ability of S. faecalis to thrive in cold environments, is evidently unrelated to adaptive changes in the viscosity of membrane lipids.Abbreviations doxyl
4-4-dimethyloxazolidine-N-oxyl
- proxyl
2,2-disubstituted 5,5-dimethylpyrrolidine-N-oxyl 相似文献
88.
Summary The characteristics of the photosynthetic apparatus of 11 Hawaiian Euphorbia species, all of which possess C4 photosynthesis but range from arid habitat, drought-deciduous shrubs to mesic or wet forest evergreen trees and shrubs, were investigated under uniform greenhouse conditions. Nine species exhibited CO2 response curves typical of C4 plants, but differed markedly in photosynthetic capacity. Light-saturated CO2 uptake rates ranged from 48 to 52 mol m-2 s-1 in arid habitat species to 18 to 20 mol m-2 s-1 in mesic and wet forest species. Two possessed unusual CO2 response curves in which photosynthesis was not saturated above intercellular CO2 pressures [p(CO2)] of 10 to 15 Pa, as typically occurs in C4 plants.Both leaf (g1) and mesophyll (gm) conductances to CO2 varied widely between species. At an atmospheric p(CO2) of 32 Pa, g1 regulated intercellular p(CO2) at 12–15 Pa in most species, which supported nearly maximum CO2 uptake rates, but did not result in excessive transpiration. Intercellular p(CO2) was higher in the two species with unusual CO2 response curves. This was especially apparent in E. remyi, which is native to a bog habitat. The regulation of g1 and intercellular p(CO2) yielded high photosynthetic water use efficiencies (P/E) in the species with typical CO2 response curves, whereas P/E was much lower in E. remyi.Photosynthetic capacity was closely related to leaf nitrogen content, whereas correlations with leaf morphological characteristics and leaf cell surface area were not significant. Thus, differences in photosynthetic capacity may be determined primarily by investment in the biochemical components of the photosynthetic apparatus rather than by differences in diffusion limitations. The lower photosynthetic capacities in the wet habitat species may reflect the lower light availability. However, other factors, such as reduced nutrient availability, may also be important. 相似文献
89.
Replication of bacteriophage lambda DNA. Examination of variants containing double origins and observation of a bias in directionality 总被引:1,自引:0,他引:1
Maria Schnös Katherine J. Denniston Frederick R. Blattner Ross B. Inman 《Journal of molecular biology》1982,159(3):441-455
Bacteriophage λ variants have been constructed that possess two λ ori sites. Replicative intermediates resulting from infection with these phages have been investigated. We find that initiation of replication from the ori site on an EcoRI fragment (containing all the DNA sequences from within the red gene to the middle of gene O) cloned in the inverted orientation is predominantly bidirectional but occurs at a decreased frequency. Double initiations were observed at low frequency. However, a second cloned ori fragment (carrying two large deletions and a small insertion) cloned in the normal orientation demonstrated insignificant levels of replication from the cloned site unless the normal ori had already initiated.A bias in directionality of λ replication has been observed. Molecules that replicate unidirectionally propagate to the right more often than to the left. If the cloned ori-containing EcoRI fragment is inserted with reversed polarity, then the bias is towards the left. Bidirectional λ replicative intermediates also appear to show a similar bias but this is superimposed on a large, apparently random, effect that results in asymmetric growing-point propagation. 相似文献
90.
Simon E. Moroney Kathlyn J. Ronaldson Alistair L. Wilkins T.G.Allan Green P.W. James 《Phytochemistry》1981,20(4):787-789
A new lichen depsidone was isolated, in the form of its triacetate derivative from the acetylated extracts of Nephroma antarcticum and has been demonstrated to be hypoconstictic acid-triacetate. Two related depsidones, hypostictic acid hyposalazinic acid, were isolated from N. australe. 相似文献