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61.
An enzyme has been isolated from human liver by DEAE-cellulose chromatography and has been shown by competitive substrate inhibition to be capable of hydrolysing synthetic beta-D-galactosides, beta-D-glucosides, beta-D-fucosides, beta-D-xylosides, and alpha-L-arabinosides. Another form of alpha-L-arabinosidase activity elutes with the major beta-D-galactosidase component on DEAE-chromatography, but has a different identity on the basis of its stability at 4 degrees C. Liver samples from patients with Gaucher's disease are deficient in beta-D-fucosidase as well as beta-D-glucosidase activity. 相似文献
62.
The basement membrane (Reichert's membrane) of the entire capsular portion of the parietal yolk sac of rat embryos was examined both morphologically and chemically at various stages of gestation. The overall microscopic and compositional analyses showed Reichert's membrane to be typical of basement membranes isolated from other tissues and species. However, with increasing gestational age (from 11.5 to 17.5 days) a number of changes involving Reichert's membrane were noted: 1. The thickness increased rapidly then declined, while the surface area increased tenfold; 2. The total protein content increased twenty-fold while the collagen content increased eight-fold. As a result, the relative collagen content declined significantly; 3. The changes in the amino acid and carbohydrate composition were consistent with the latter finding.The observations listed above were evaluated in light of their possible relevance to an understanding of the morphogenesis of basement membranes during development, and to the possible mechanisms involved in pathogenesis of basement membrane dysfunction. 相似文献
63.
The tissue distribution and some properties of human alpha-mannosidase (alpha-D-mannoside mannohydrolase EC 3.2.1.24) have been studied. The acidic forms of the enzyme were fairly stable, whereas the neutral forms easily lost enzymic activity. The acidic forms were sensitive to neuraminidase but the neutral forms were unaffected. The experiments indicate that the acidic components are closely related to each other, differing only in sialic acid content and possibly conformation. The neutral forms of the enzyme are probably quite different from the acidic forms both in structure and cellular function. 相似文献
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65.
Larvae removed at one-day intervals from laboratory infected intermediate hosts provided material for a comparative study of presomal development in Prosthorhynchus formosus (Van Cleave, '18) Travassos, '26, Prosthenorchis elegans (Diesing, 1851) Travassos, '15, and Moniliformis dubius Meyer, '33. Acanthellae begin development soon after entering intermediate hosts' hemocoels, and by the 18th day all three species possess three nuclear masses representing primordia of the proboscis, proboscis receptacle and ganglion, and trunk musculature and genitalia. Presomal development of P. formosus and P. elegans results in structures concurring with morphology of other adult palaeacanthocephalans and archiacanthocephalans. Development of M. dubius, however, differs from that of other archiacanthocephalans in that the muscular receptacle wall lines the entire surface of the nonmuscular sheath, failing to form a ventral cleft characteristic of other archiacanthocephalans. Unlike receptacle protrusor muscles of other archiacanthocephalan species, those of M. dubius spiral around the receptacle as they extend posteriad to attach individually to a pouchlike, muscular thickening at the receptacle's base. These protrusor muscles are distinct from the receptacle wall, as attested by their development alongside neck retractor muscles, not from the receptacle primordium, and the manner in which they are left to trail behind the receptacle when it is drawn anteriorly into the proboscis during larval development. The proboscis receptacle of M. dubius should not be thought of as being double-walled, as envisioned by previous workers. 相似文献
66.
Eric M. Lind Elizabeth Borer Eric Seabloom Peter Adler Jonathan D. Bakker Dana M. Blumenthal Mick Crawley Kendi Davies Jennifer Firn Daniel S. Gruner W. Stanley Harpole Yann Hautier Helmut Hillebrand Johannes Knops Brett Melbourne Brent Mortensen Anita C. Risch Martin Schuetz Carly Stevens Peter D. Wragg 《Ecology letters》2013,16(4):513-521
Plant growth can be limited by resource acquisition and defence against consumers, leading to contrasting trade‐off possibilities. The competition‐defence hypothesis posits a trade‐off between competitive ability and defence against enemies (e.g. herbivores and pathogens). The growth‐defence hypothesis suggests that strong competitors for nutrients are also defended against enemies, at a cost to growth rate. We tested these hypotheses using observations of 706 plant populations of over 500 species before and following identical fertilisation and fencing treatments at 39 grassland sites worldwide. Strong positive covariance in species responses to both treatments provided support for a growth‐defence trade‐off: populations that increased with the removal of nutrient limitation (poor competitors) also increased following removal of consumers. This result held globally across 4 years within plant life‐history groups and within the majority of individual sites. Thus, a growth‐defence trade‐off appears to be the norm, and mechanisms maintaining grassland biodiversity may operate within this constraint. 相似文献
67.
Occupational and environmental pulmonary exposure to carbon nanotubes (CNT) is considered to be a health risk with a very low threshold of tolerance as determined by the United States Center for Disease Control. Immortalized airway epithelial cells exposed to CNTs show a diverse range of effects including reduced viability, impaired proliferation, and elevated reactive oxygen species generation. Additionally, CNTs inhibit internalization of targets in multiple macrophage cell lines. Mice and rats exposed to CNTs often develop pulmonary granulomas and fibrosis. Furthermore, CNTs have immunomodulatory properties in these animal models. CNTs themselves are proinflammatory and can exacerbate the allergic response. However, CNTs may also be immunosuppressive, both locally and systemically. Studies that examined the relationship of CNT exposure prior to pulmonary infection have reached different conclusions. In some cases, pre-exposure either had no effect or enhanced clearance of infections while other studies showed CNTs inhibited clearance. Interestingly, most studies exploring this relationship use pathogens which are not considered primary pulmonary pathogens. Moreover, harmony across studies is difficult as different types of CNTs have dissimilar biological effects. We used Pseudomonas aeruginosa as model pathogen to study how helical multi-walled carbon nanotubes (HCNTs) affected internalization and clearance of the pulmonary pathogen. The results showed that, although HCNTs can inhibit internalization through multiple processes, bacterial clearance was not altered, which was attributed to an enhanced inflammatory response caused by pre-exposure to HCNTs. We compare and contrast our findings in relation to other studies to gauge the modulation of pulmonary immune response by CNTs. 相似文献
68.
69.
Xiben Wang Mingzhe Z. Che Hala B. Khalil Brent D. McCallum Guus Bakkeren Christof Rampitsch Barry J. Saville 《Environmental microbiology》2020,22(7):2956-2967
Reactive oxygen species (ROS) play an important role during host–pathogen interactions and are often an indication of induced host defence responses. In this study, we demonstrate for the first time that Puccinia triticina (Pt) generates ROS, including superoxide, H2O2 and hydroxyl radicals, during wheat infection. Through pharmacological inhibition, we found that ROS are critical for both Pt urediniospore germination and pathogenic development on wheat. A comparative RNA-Seq analysis of different stages of Pt infection process revealed 291 putative Pt genes associated with the oxidation–reduction process. Thirty-seven of these genes encode known proteins. The expressions of five Pt genes, including PtNoxA, PtNoxB, PtNoxR, PtCat and PtSod, were subsequently verified using RT-qPCR analysis. The results show that the expressions of PtNoxA, PtNoxB, PtNoxR, PtCat and PtSod are up-regulated during urediniospore germination. In comparison, the expressions of PtNoxA, PtNoxB, PtNoxR and PtCat are down-regulated during wheat infection from 12 to 120 h after inoculation (HAI), whereas the expression of PtSod is up-regulated with a peak of expression at 120 HAI. We conclude that ROS are critical for the full virulence of Pt and a coordinate down-regulation of PtNox genes may be important for successful infection in wheat. 相似文献
70.
Steven H. Ferguson David J. Yurkowski Brent G. Young Aaron T. Fisk Derek C. G. Muir Xinhua Zhu Gregory W. Thiemann 《Ecography》2020,43(10):1521-1535
Ecological theory suggests that demographic responses by populations to environmental change vary depending on whether individuals inhabit central or peripheral regions within the species’ geographic range. Here, we tested this prediction by comparing a population of ringed seals Pusa hispida located at high latitudes as part of their core range (core) with a population located at the southern extremity of their range (peripheral). First, we compared the two regions’ environmental trends in timing of sea-ice breakup and freeze-up, open-water duration and the North Atlantic Oscillation (NAO). We found that the core region shifted to progressively warmer conditions in the early 1990s; whereas, in the peripheral region, the warming trend shifted in 1999 to one with no warming trend but high inter-annual variability. Next, we examined how body condition, inferred from blubber depth, responded to temporal changes in sea-ice and climatic variables – variables that have been shown to influence ringed seal demography. Core seals displayed minimal seasonal changes in body condition; whereas peripheral seals displayed a 20–60% amplitude seasonal change in body condition with a phase shift to earlier initiation of fat accumulation and loss. Finally, we tested for interannual differences and found that both core and peripheral seals responded similarly with decreased body condition following more positive NAO. Environmental variables influenced body condition in opposite directions between the two regions with core seals declining in body condition with later spring breakup and shorter open-water duration, whereas peripheral seals showed opposite relationships. Seals living at the core likely benefit from an evolved match between adaptation and environmental variation resulting in dampened seasonal and interannual fluctuations in body condition. Knowledge of how different populations respond to environmental change depending on geographic location within a species range can assist in anticipating population specific responses to climate warming. 相似文献