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31.
An experimental investigation of the low hydration phase properties of phospholipid mixtures is described. 2H (D2O) NMR, X-ray diffraction and differential scanning calorimetry have been used to elucidate the phase properties of mixtures of the mixed chain phospholipids palmitoyloleoylphosphatidylcholine (POPC) and palmitoyloleoylphosphatidylethanolamine (POPE). At 10% hydration pure POPE exhibited a HII phase above 330 K, a fluid lamellar phase below 315 K, and a minimally hydrated crystalline phase below 300 K. For the 1:1 mixture, the samples exhibited only gel or fluid phases between 270 K and 360 K for hydrations in the range 15% to 30%. Below 15% hydration the mixture exhibited two fluid phases with different repeat spacings, as predicted previously. 相似文献
32.
Effect of Hydrogenase and Mixed Sulfate-Reducing Bacterial Populations on the Corrosion of Steel 总被引:4,自引:2,他引:2 下载免费PDF全文
Richard D. Bryant Wayne Jansen Joe Boivin Edward J. Laishley J. William Costerton 《Applied microbiology》1991,57(10):2804-2809
The importance of hydrogenase activity to corrosion of steel was assessed by using mixed populations of sulfate-reducing bacteria isolated from corroded and noncorroded oil pipelines. Biofilms which developed on the steel studs contained detectable numbers of sulfate-reducing bacteria (104 increasing to 107/0.5 cm2). However, the biofilm with active hydrogenase activity (i.e., corrosion pipeline organisms), as measured by a semiquantitative commercial kit, was associated with a significantly higher corrosion rate (7.79 mm/year) relative to noncorrosive biofilm (0.48 mm/year) with 105 sulfate-reducing bacteria per 0.5 cm2 but no measurable hydrogenase activity. The importance of hydrogenase and the microbial sulfate-reducing bacterial population making up the biofilm are discussed relative to biocorrosion. 相似文献
33.
Productivity and longevity decreased in a laboratory colony of the parasitoid wasp Microplitis croceipes (Cresson) (Hymenoptera: Braconidae). Using light microscopy, it was determined that the colony was free of microsporidia. However, samples of the colony examined for pathogens by electron microscopy revealed three types of viruses: a nonpathogenic polydnavirus which is produced by all female wasps; a nonoccluded baculovirus which is pathogenic to late-stage pupae and adults; and a picorna-like virus which is present in larvae, pupae, and adults. The nonoccluded baculovirus was eliminated from the laboratory colony of M. croceipes by selection of progeny from wasps which had oviposited within 2 to 3 days after emergence from the cocoons and which had lived for at least 14 days post-emergence. Upon death, the wasps were examined by negative stain electron microscopy and only progeny from baculovirus-free wasps were retained. Parasitoid colonies should be systematically examined for pathogenic viruses that may reduce their productivity and efficacy as biological control agents. In addition, exotic parasitoids and predators should be evaluated for viruses and other pathogens while in quarantine. 相似文献
34.
The morphology and distribution of a variety of types of nucleus in the apex, in young and mature gametangia, and in older regions of the Cymopolia cell were studied by light and electron microscopy. Spherical and convoluted nuclei 2–7μm in diameter were observed in apical regions of the vegetative siphon. Nuclei 4 μm in diameter were present in the young primary laterals and in developing gametangia. A single characteristic nucleus migrates from the siphon into the primary lateral of the second basipetal whorl. It is further transported into one of several possible secondary laterals and determines the development of gametangia which become multinucleate in the fourth or fifth whorls. Nuclei are characterized by size, shape, nucleolar morphology, nucleoplasmic inclusions and the ultrastructure of the perinuclear cytoplasm. Although no “primary nucleus” characteristic of the uninucleate genera, Acetabularia and Batophora was observed, some nuclei of Cymopolia have features in common with secondary nuclei of these genera. 相似文献
35.
Abstract: The enzyme 2',3'-cyclic nucleotide 3'-phosphodiesterase (EC 3.1.4.37) has been isolated from an acetone powder of human subcortical white matter. The yield was about 11 mg from 28 g of powder and a specific activity of 213 unitdmg protein was obtained using 2',3'-cyclic CMP as the substrate. A major protein band of molecular weight approx. 96,000 was found by gel electrophoresis under nonreducing conditions. However, two distinct protein bands of molecular weight 46,000 ± 1400 and 48,000 ± 1400 were observed when the protein sample was reduced with 10 mM-dithiothreitol and subjected to electrophoresis in more restrictive 12-15% polyacrylamide-SDS gels. This molecular weight is lower than that previously reported for the bovine enzyme. Antibodies against the purified human enzyme have been raised in New Zealand white rabbits. 相似文献
36.
John T. Sullivan Charles S. Richards Kian Joe Lie Donald Heyneman 《International journal for parasitology》1981,11(6):481-484
Sullivan J. T., Richards C. S., Lie K. J. and Heyneman D. 1981. Schistosoma mansoni, NIH-Sm-PR-2 strain, in non-susceptible Biomphalaria glabrata: Protection by Echinostoma paraensei. International journal for Parasitology11:481–484. Among seven inbred genetic stocks of Biomphalaria glabrata that are non-susceptible for the NIH-Sm-PR-2 strain of Schistosoma mansoni (PR-2), five stocks revert to nearly complete susceptibility when first infected with Echinostoma paraensei. These include both stocks in which PR-2 sporocysts are normally destroyed within 3–7 days, and stocks in which sporocysts often survive undeveloped for at least 3 weeks. Hence, these five stocks are resistant to but physiologically suitable for the development of PR-2. Of the two remaining stocks, one remains partly non-susceptible to PR-2, since less than 50 % of echinostome-infected snails revert to susceptibility, while the other stock remains completely non-susceptible to PR-2 following echinostome infection, due perhaps to a high level of residual resistance and/or unsuitability. 相似文献
37.
In juvenile albino Biomphalaria glabrata snails exposed for the first time to Echinostoma lindoense miracidia, and observed to be resistant, the sporocysts migrated to the heart at the same speed as they did in susceptible snails. However, in resistant snails the sporocysts were soon destroyed in the heart by amebocyte clumps. When these snails were then re-exposed to miracidia of the same species of trematode, the sporocysts were quickly destroyed soon after miracidial penetration, chiefly in the head-foot region. This strongly accelerated tissue reaction appears to have been induced by the previous contact with the same parasite. The sensitization of the snail tissues was highly specific: the hosts remained susceptible to Schistosoma mansoni and Paryphostomum segregation (Echinostomatidae), although partial resistance was observed against Echinostoma paraensei and E. liei, which are closely related to E. lindoense. 相似文献
38.
Robert J. Standerfer Marvin B. Rittenberg Ching J. Chern Joe W. Templeton John A. Black 《Biochemical genetics》1975,13(5-6):341-351
We have compared the solubility, kinetic, immunological, and electrophoretic properties of erythrocyte pyruvate kinase from normal dogs and Basenji dogs with congenital hemolytic anemia due to pyruvate kinase deficiency. Differences can be detected between the two enzymes by all methods. The enzyme from the affected animals has a greater solubility in ammonium sulfate. It has a lower K m for phosphoenolpyruvate, while the K m for ADP is increased. This enzyme is not inhibited by ATP or activated by fructose 1,6-diphosphate. The enzyme from the affected animals has none of the allosteric properties characteristic of the normal canine enzyme. No difference can be detected by enzyme inactivation with rabbit antiserum against the human erythrocyte enzyme, but a slight spur is observed on comparison of the two enzymes by Ouchterlony immunodiffusion. The enzymes also differ in their electrophoretic mobilities on starch gel electrophoresis. 相似文献
39.
Fredrick C. Colley Lie Kian Joe Viqar Zaman E.U. Canning 《Journal of invertebrate pathology》1975,26(1):11-20
A nuclear-polyhedrosis virus (NPV) of the silkworm, Bombyx mori, which forms an icosahedral inclusion body, was transmitted to larvae of the rice stem borer, Chilo suppressalis. Serial passages of Bombyx NPV in the alternate host by injecting the supernatant of diseased hemolymph produced inclusion bodies with cuboidal and other shapes that differed from the original shape formed in Bombyx. These different shapes increased with times of passages, and after the twelfth passage, only cuboidal inclusion bodies were formed. The icosahedral inclusion bodies in B. mori and the cuboidal inclusion bodies in C. suppressalis occluded singly enveloped virions of the same size (350 × 75 nm), but the cuboidal inclusion bodies contained only a few virions and a large number of membraneous spherical structures. The formation process of the cuboidal inclusion body differed from that of the icosahedral. At first, irregularly branched inclusion bodies containing “vacant” spaces appeared in the infected nuclei. The bodies grew larger with the deposition of protein in the spaces between the branches, and this was accompanied with the occlusion of a large number of membraneous structures formed in the vicinity of the inclusion bodies, which became cuboidal in shape. 相似文献
40.
Aaron Mendez-Bermudez Liudmyla Lototska Melanie Pousse Florent Tessier Oliver Croce Chrysa
M Latrick Veronica Cherdyntseva Joe Nassour Jiang Xiaohua Yiming Lu Corinne Abbadie Sarantis Gagos Jing Ye Eric Gilson 《Nucleic acids research》2022,50(13):7493
Cellular senescence triggers various types of heterochromatin remodeling that contribute to aging. However, the age-related mechanisms that lead to these epigenetic alterations remain elusive. Here, we asked how two key aging hallmarks, telomere shortening and constitutive heterochromatin loss, are mechanistically connected during senescence. We show that, at the onset of senescence, pericentromeric heterochromatin is specifically dismantled consisting of chromatin decondensation, accumulation of DNA breakages, illegitimate recombination and loss of DNA. This process is caused by telomere shortening or genotoxic stress by a sequence of events starting from TP53-dependent downregulation of the telomere protective protein TRF2. The resulting loss of TRF2 at pericentromeres triggers DNA breaks activating ATM, which in turn leads to heterochromatin decondensation by releasing KAP1 and Lamin B1, recombination and satellite DNA excision found in the cytosol associated with cGAS. This TP53–TRF2 axis activates the interferon response and the formation of chromosome rearrangements when the cells escape the senescent growth arrest. Overall, these results reveal the role of TP53 as pericentromeric disassembler and define the basic principles of how a TP53-dependent senescence inducer hierarchically leads to selective pericentromeric dismantling through the downregulation of TRF2. 相似文献