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881.
Persistence of phase coexistence in disaturated phosphatidylcholine monolayers at high surface pressures 下载免费PDF全文
Prior reports that the coexistence of the liquid-expanded (LE) and liquid-condensed (LC) phases in phospholipid monolayers terminates in a critical point have been compromised by experimental difficulties with Langmuir troughs at high surface pressures and temperatures. The studies reported here used the continuous interface of a captive bubble to minimize these problems during measurements of the phase behavior for monolayers containing the phosphatidylcholines with the four different possible combinations of palmitoyl and/or myristoyl acyl residues. Isothermal compression produced surface pressure-area curves for dipalmitoyl phosphatidylcholine (DPPC) that were indistinguishable from previously published data obtained with Langmuir troughs. During isobaric heating, a steep increase in molecular area corresponding to the main LC-LE phase transition persisted for all four compounds to 45 mN/m, at which collapse of the LE phase first occurred. No other discontinuities to suggest other phase transitions were apparent. Isobars for DPPC at higher pressures were complicated by collapse of the monolayer, but continued to show evidence up to 65 mN/m for at least the onset of the LC-LE transition. The persistence of the main phase transition to high surface pressures suggests that a critical point for these monolayers of disaturated phospholipids is either nonexistent or inaccessible at an air-water interface. 相似文献
882.
Enteropathogenic Escherichia coli (EPEC) triggers a large release of adenosine triphosphate (ATP) from host intestinal cells and the extracellular ATP is broken
down to adenosine diphosphate (ADP), AMP, and adenosine. Adenosine is a potent secretagogue in the small and large intestine.
We suspected that ecto-5′-nucleotidase (CD73, an intestinal enzyme) was a critical enzyme involved in the conversion of AMP
to adenosine and in the pathogenesis of EPEC diarrhea. We developed a nonradioactive method for measuring ecto-5′-nucleotidase
in cultured T84 cell monolayers based on the detection of phosphate release from 5′-AMP. EPEC infection triggered a release
of ecto-5′-nucleotidase from the cell surface into the supernatant medium. EPEC-induced 5′-nucleotidase release was not correlated
with host cell death but instead with activation of phosphatidylinositol-specific phospholipase C (PI-PLC). Ecto-5′-nucleotidase
was susceptible to inhibition by zinc acetate and by α,β-methylene-adenosine diphosphate (α,β-methylene-ADP). In the Ussing
chamber, these inhibitors could reverse the chloride secretory responses triggered by 5′-AMP. In addition, α,β-methylene-ADP
and zinc blocked the ability of 5′-AMP to stimulate EPEC growth under nutrient-limited conditions in vitro. Ecto-5′-nucleotidase
appears to be the major enzyme responsible for generation of adenosine from adenine nucleotides in the T84 cell line, and
inhibitors of ecto-5′-nucleotidase, such as α,β-methylene-ADP and zinc, might be useful for treatment of the watery diarrhea
produced by EPEC infection. 相似文献
883.
The development of a genetic map for meadowfoam comprised of amplified fragment length polymorphisms
Katengam S Crane JM Knapp SJ 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2002,104(1):92-96
Limnanthes alba Benth. (meadowfoam), a diploid (x=5) winter annual, produces novel very long-chain seed oils (C20 and C22) with less than 2% saturated fatty acids. The first genetic map of meadowfoam, a recently domesticated species, is described
herein. Two phenotypically diverse inbred lines, OMF40–11 (L. alba ssp. alba) and OMF64 (L. alba ssp. versicolor), were screened for amplified fragment length polymorphisms (AFLPs) using 16 primer combinations. Twenty three percent of
the AFLP bands (415 out of 1,801) were polymorphic between OMF40–11 and OMF64. One hundred (OMF40–11×OMF64)×OMF64 BC1 progeny were genotyped for 107 polymorphic AFLP markers produced by nine AFLP primer combinations. One hundred and three
AFLP loci amalgamated into five linkage groups with 14 to 28 loci per linkage group (four loci segregated independently).
The map was 698.5-cM long with a mean interlocus spacing of 6.7 cM and no dense clustering of loci. The segregation ratios
for 25 loci (23.2%) were significantly distorted. Twenty one of the distorted loci (84%) had an excess of L. alba ssp. versicolor (recurrent parent) alleles. The distorted loci, apart from one locus on linkage group 4, were distally clustered on both
ends of linkage groups 1, 4 and 5. The development of the map was facilitated by the small chromosome number, an abundance
of restriction site polymorphisms between the two subspecies (23%), and a high multiplex ratio of the AFLP markers (112 per
primer combination).
Received: 16 October 2000 / Accepted: 18 April 2001 相似文献
884.
Else Marie Friis Kaj Raunsgaard Pedersen Peter R. Crane 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2010,365(1539):369-382
In the second half of the nineteenth century, pioneering discoveries of rich assemblages of fossil plants from the Cretaceous resulted in considerable interest in the first appearance of angiosperms in the geological record. Darwin''s famous comment, which labelled the ‘rapid development’ of angiosperms an ‘abominable mystery’, dates from this time. Darwin and his contemporaries were puzzled by the relatively late, seemingly sudden and geographically widespread appearance of modern-looking angiosperms in Late Cretaceous floras. Today, the early diversification of angiosperms seems much less ‘rapid’. Angiosperms were clearly present in the Early Cretaceous, 20–30 Myr before they attained the level of ecological dominance reflected in some mid-Cretaceous floras, and angiosperm leaves and pollen show a distinct pattern of steadily increasing diversity and complexity through this interval. Early angiosperm fossil flowers show a similar orderly diversification and also provide detailed insights into the changing reproductive biology and phylogenetic diversity of angiosperms from the Early Cretaceous. In addition, newly discovered fossil flowers indicate considerable, previously unrecognized, cryptic diversity among the earliest angiosperms known from the fossil record. Lineages that today have an herbaceous or shrubby habit were well represented. Monocotyledons, which have previously been difficult to recognize among assemblages of early fossil angiosperms, were also diverse and prominent in many Early Cretaceous ecosystems. 相似文献
885.
886.
887.
A double layer of protein in mitochondrial cristae 总被引:2,自引:0,他引:2
888.
F. L. Crane H. Roberts A. W. Linnane H. Löw 《Journal of bioenergetics and biomembranes》1982,14(3):191-205
Both respiratory-competent and respiratory-deficient yeast cells reduce external ferricyanide. The reduction is stimulated by ethanol and inhibited by the alcohol dehydrogenase inhibitor, pyrazole. The reduction of ferricyanide is not inhibited by inhibitors of mitochondrial or microsomal ferricyanide reduction. Cells in exponential-phase growth show a much higher rate of ferricyanide reduction. The reduction of ferricyanide is accompanied by increased release of protons by the yeast cells. We propose that the ferricyanide reduction is carried out by a transmembrane NADH dehydrogenase. 相似文献
889.
890.
The role of catalase in lipid metabolism has been studied by means of a comparison of the turnover characteristics of the major lipid classes in the normal mouse with those of animals in which the catalase activity had been inhibited and blocked by aminotriazole and allylisopropylacetamide. Double isotope ratios were determined in the lipid fractions of several tissues following the injection of labeled glycerol, and a number of significant differences were identified between these treatments. Since catalase is recognized as an integral component of the peroxisomal pathway of fatty acid oxidation, these results may be taken as indicating that interruption of the process of peroxisomal beta-oxidation in this manner cause extensive perturbations of lipid metabolism in the living animal, and these perturbations extend well beyond those tissues where the predominant localization of these organelles occurs. The concept which derives from these data--that of a significant regulatory role of peroxisomes in relation to the overall balance of lipid metabolism in the animal body--is described and discussed. 相似文献