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281.
Discrete resource polymorphisms occur in various vertebrate species and probably occur more frequently than is generally appreciated. They are manifested in a number of ways, including morphological, behavioral and life history characters. Research on a number of unrelated taxa suggests that resource polymorphisms may be underestimated as a diversifying force and potentially play important roles in population divergence and initial steps in speciation. In an ecological context, they are important in resource partitioning and reducing intraspecific competition. Recent research suggests that the mechanisms maintaining these polymorphisms may be similar in diverse taxa, that phenotypic plasticity is important, and that some are under simple genetic control. 相似文献
282.
Cloning of the mgtE Mg2+ transporter from Providencia stuartii and the distribution of mgtE in gram-negative and gram-positive bacteria. 总被引:1,自引:1,他引:0 下载免费PDF全文
D E Townsend A J Esenwine J George rd D Bross M E Maguire R L Smith 《Journal of bacteriology》1995,177(18):5350-5354
The MM281 strain of Salmonella typhimurium possesses mutations in each of its three Mg2+ transport systems, requires 100 mM Mg2+ for growth, and was used to screen a genomic library from the gram-negative bacterium Providencia stuartii for clones that could restore the ability to grow without Mg2+ supplementation. The clones obtained also conferred sensitivity to Co2+, a phenotype similar to that seen with the S. typhimurium corA Mg2+ transport gene. The sequence of the cloned P. stuartii DNA revealed the presence of a single open reading frame, which was shown to express a protein with a gel molecular mass of 37 kDa in agreement with the deduced size of 34 kDa. Despite a phenotype similar to that of corA and the close phylogenetic relationship between P. stuartii and S. typhimurium, this new putative Mg2+ transporter lacks similarity to the CorA Mg2+ transporter and is instead homologous to MgtE, a newly discovered Mg2+ transport protein from the gram-positive bacterium Bacillus firmus OF4. The distribution of mgtE in bacteria was studied by Southern blot hybridization to PCR amplification products. In contrast to the ubiquity of the corA gene, which encodes the dominant constitutive Mg2+ influx system of bacteria, mgtE has a much more limited phylogenetic distribution. 相似文献
283.
S. A. Smith T. Caceci † H. E-S. Marei ‡ H. A. El-Habback § 《Journal of fish biology》1995,46(2):241-254
In the angelfish ( Pterophyllum scalare scalare ) numerous rodlet cells were found in the large post-orbital blood vessel caudal to the eye and in the surrounding extravascular space. Within the vessel the rodlet cells formed striking regular arrays, along the inner aspect of the wall. The rodlets within the cells were positive to PAS but negative to Sudan Black B, Masson's, and the Fuelgen stain. The capsule around the cells was negative for all these stains. These rodlet cells appeared to be traversing the vessel endothelium, and to be pushing the endothelium aside without damaging it. Some discharged their contents into the vessel, but we never observed the release of intact rodlets. The nuclei of rodlet cells in actual contact with the vessel were at the end of the cell more distant from the endothelial wall. Cell-to-cell adhesion structures or communications junctions between rodlet cells and the endothelium were not evident. A putative rodlet cell precursor in the extravascular space contained large electron-dense granules, and extended pseudopodia that contacted nearby rodlet cells. Based on their morphology, tissue distribution, and their behaviour, we conclude that the rodlet cell is an endogeneous teleost cell type, and possibly represents a form of matured granulocyte. 相似文献
284.
Goupille Ronald E.; Smith April E.; Toida Toshihiko; Linhardt Robert J. 《Glycobiology》1997,7(2):231-239
Porcine intestinal mucosal heparan sulfate was exhaustivelydepolymerized on a large scale using beparin lyase II (heparinaseII) or heparin lyase III (heparitinase, EC 4.2.2.8
[EC]
). The oligosaccharidemixtures formed with each enzyme were fractionated by low pressuregel permeation chromatography. Size-uniform mixtures of disaccharides,tetrasaccharides, and hexasaccharides were obtained. Each size-fractionatedmixture was then purified on the basis of charge by repetitivesemipreparative strong-anion-exchange high-performance liquidchromatography. This approach has led to the isolation of 13homogenous oligosaccharides. The purity of each oligosaccharidewas demonstrated by the presence of a single peak on analyticalstrong-anion-exchange high-performance liquid chromatographyand reversed polarity capillary electrophoresis. The structuresof these oligosaccharides were established using 500 MHz one-and two-dimensional nuclear magnetic resonance spectroscopy.Three of the thirteen structures that were solved were novelwhile the remaining 10 have been previously described. All ofthe structures obtained using heparin lyase III contained a 相似文献
285.
Leuconostoc mesenteroides B-1355 produced at least three glucosyltransferases (GTFs). We previously identified GTF-2 as alternansucrase and GTF-3 as fraction L dextransucrase. We here show that GTF-1 is a previously unreported sucrase that synthesized water-insoluble dextran. Our evidence consisted of the following. (i) GTF-1 was a major component and GTF-2 was a minor component of culture supernatant fractions, but supernatant fractions actively synthesized water-insoluble glucan. (ii) GTF-1 and culture supernatants produced an unusual high-pressure liquid chromatography pattern of malto-oligosaccharides that was not reproduced by GTF-2-GTF-3 mixtures. (iii) GTF-2, GTF-3, and GTF-2-GTF-3 mixtures did not synthesize insoluble glucan from sucrose. Nearly all of the alternansucrase in young (less than 17-h) cultures was associated with the cells. 相似文献
286.
Energy-dispersive X-ray analysis of the extracellular cadmium sulfide crystallites of Klebsiella aerogenes 总被引:4,自引:0,他引:4
Justin D. Holmes Peter R. Smith Richard Evans-Gowing David J. Richardson David A. Russell John R. Sodeau 《Archives of microbiology》1995,163(2):143-147
Klebsiella aerogenes forms electron-dense partieles on the cell surface in response to the presence of cadmium ions in the growth medium. These particles ranged from 20 to 200 nm in size, and quantitative energy dispersive X-ray analysis established that they comprise cadmium and sulfur in a 1:1 ratio. This observation leads to the conclusion that the particles are cadmium sulfide crystallites. A combination of atomic absorption spectroscopy, inductively coupled plasma mass spectrometry, and acid-labile sulfide analysis revealed that the total intracellular and bound extracellular cadmium:sulfur ratio is also 1:1, which suggests that the bulk of the cadmium is fixed as extracellular cadmium sulfide. The tolerance of K. acrogenes to cadmium ions and the formation of the cadmium sulfide crystallites were dependent on the buffer composition of the growth medium. The addition of cadmium ions to phosphate-buffered media resulted in cadmium phosphate precipitates that remove the potentially toxic cadmium ions from the growth medium. Electrondense particles formed on the surfaces of bacteria grown under these conditions were a combination of cadmium sulfide and cadmium phosphates. The specific bacterial growth rate in the exponential phase of batch cultures was not affected by up to 2mM cadmium in Tricine-buffered medium, but formation of cadmium sulfide crystallites was maximal during the stationary phase of batch culture. Cadmium tolerance was much lower (10 to 150 M) in growth media buffered with Tris, Bistris propane, Bes, Tes, or Hepes. These results illustrate the importance of considering medium composition when comparing levels of bacterial cadmium tolerance.Abbreviations
EDXA
Energy dispersive X-ray analysis
-
AAS
Atomic absorption spectroscopy
-
TEM
Transmission electron microscopy
-
SEM
Scanning electron microscopy
-
ICP-MS
Inductively coupled plasma mass spectrometry
-
ALSA
Acid-labile sulfide analysis 相似文献
287.
288.
The operational sex ratio (OSR), an important determinant of the intensity of sexual selection, can vary with the population sex ratio and the potential reproductive rates of males and females. In parental teleosts, different forms of brood cannibalism, filial and non-kin, could affect the potential reproductive rates of males and females, and thereby the OSR. The direction of the effect of brood cannibalism on the OSR would depend on the sex of the cannibal and the parent. No evidence has been found that brood cannibalism can affect the OSR by altering the sex ratio. 相似文献
289.
J M Smith 《Tissue & cell》1984,16(1):43-51
A staining procedure has been developed for imaging actin-containing structures in thick plastic sections in the electron microscope. The stress fibres of a fibroblastic cell line were used as a model system, and were first characterized immunocytochemically. After fixation of cells in formaldehyde, mordanting in a solution of gadolinium chloride allows stress fibres to be stained for light microscopy with haematoxylin. A brief exposure to a solution of ammonium paramolybdate renders haematoxylin-stained structures sufficiently electron-dense to be imaged in 1 micron thick plastic sections in a JEOL 200CX electron microscope, operating at 200 kV, and possibly in conventional instruments operating at 100 kV, particularly if equipped with a lanthanum hexaboride source. 相似文献
290.
Effects of an anion channel blocker, 4, 4'-diisothiocyano-2,2'-disulfonic acid stilbene (DIDS), on human neutrophil function 总被引:1,自引:0,他引:1
R J Smith B J Bowman S S Iden 《Biochemical and biophysical research communications》1984,120(3):964-972
We investigated the capacity of DIDS to influence degranulation and superoxide anion (O-2) generation by human neutrophils exposed to soluble, surface-active stimuli. DIDS caused a concentration-related (25-200 microM) inhibition of myeloperoxidase (MPO) release from N-formyl-methionyl-leucyl-phenylalanine (FMLP), 5(S), 12(R)-dihydroxy-6, 14-cis-8, 10-trans-eicosatetraenoic acid (LTB4), 1-0-hexadecyl/octadecyl-2-0-acetyl-sn-glyceryl-3-phosphorylcholine (AGEPC) and phorbol myristate acetate (PMA)-stimulated neutrophils. In contrast, DIDS had no effect on O-2 production by FMLP and PMA activated cells, whereas it enhanced LTB4 and AGEPC-elicited O-2 generation. The respective effects of DIDS on these neutrophil activities were reversed by washing the cells prior to exposure to stimulus. Thus, DIDS represents a useful pharmacologic probe for investigating the role(s) of anions in the mechanisms of neutrophil activation with structurally and chemically dissimilar stimuli. 相似文献