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1.
A recording fluorometric assay for dihydrofolate reductase is described. The technique measures the appearance of product, tetrahydrofolate, as the reaction proceeds. The assay can be accomplished with as little as 2 pmol of enzyme and is sufficiently sensitive to allow accurate kinetic studies using very low concentrations of substrate. Kinetic studies of both purified and crude preparations of enzyme are reported. 相似文献
2.
Hydroid defenses against predators: the importance of secondary metabolites versus nematocysts 总被引:4,自引:2,他引:2
Marine hydroids are commonly thought to be defended by stinging organelles called nematocysts that penetrate predator tissues
and inject proteinaceous venoms, but not all hydroids possess these nematocysts. Although an increasing number of bioactive
secondary metabolites have been isolated from marine hydroids, ecological roles of these compounds are poorly known. To test
the hypothesis that nematocysts and noxious secondary metabolites represent alternative defenses against predation, we examined
hydroids from North Carolina, United States for: (1) the palatability of whole polyps before and after nematocysts had been
deactivated; (2) the palatability of their chemical extracts; and (3) their nutritional value in terms of organic content,
protein content, and levels of refractory structural material (chitin). All hydroids were avoided by a generalist predator,
the pinfish Lagodon rhomboides, compared with palatable control foods. Two of these (Halocordyle disticha and Tubularia crocea) became palatable after being treated with potassium chloride to discharge their nematocysts, suggesting that these species
rely on nematocysts for defenses against predators. Chemical extracts from nematocyst-defended species had no effect on fish
feeding. The four species that remained unpalatable after nematocysts had been discharged (Corydendrium parasiticum, Eudendrium carneum, Hydractinia symbiolongicarpus, Tridentata marginata) possessed chemical extracts that deterred feeding by pinfish. We have isolated and characterized the structures of the deterrent
metabolites in two of these species. We found no differences in nutritional content or levels of chitin between nematocyst-defended
and chemically defended species, and no evidence that either of these played a role in the rejection of hydroids as prey.
Our results suggest that, among hydroids, chemical defenses may be at least as common as nematocyst-based defenses and that
the two may represent largely alternative defensive strategies. The four hydroid species with deterrent extracts represent
four families and both sub-orders of hydroids, suggesting that chemical defenses in this group may be widespread and have
multiple origins.
Received: 25 May 1999 / Accepted: 1 February 2000 相似文献
3.
Fifteen out of 50 species of ascid mites (30%) that we collected from four synanthropic and seven natural habitats in North America and Australia existed as all-female populations. In contrast to the predictions of the biotic uncertainty hypothesis (i.e. that parthenogenetic species are rare, restricted in distribution and survive through dispersal ability), we found that parthenogentic ascid mites were present in ten out of 11 habitats sampled, but were not superior colonists. In a glasshouse experiment, pasteurized soil in pots was colonized first by bisexual species and only later by all-female species. Furthermore, a habitat requiring strong dispersal abilities (decaying fungal sporocarps) lacked parthenogenetic species and a review of literature and collections indicated that all-female ascid species rarely form the phoretic associations with insects necessary to exploit patchy and ephemeral resources. The assumptions that parthenogens are reproductively superior to but competitively inferior to sexual relatives were not supported by experiments comparing a bisexual and an all-female species of Lasioseius. 相似文献
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Moushimi Amaya Forrest Keck Michael Lindquist Kelsey Voss Lauren Scavone Kylene Kehn-Hall Brian Roberts Charles Bailey Connie Schmaljohn Aarthi Narayanan 《PloS one》2015,10(4)
Many viruses have been implicated in utilizing or modulating the Ubiquitin Proteasome System (UPS) to enhance viral multiplication and/or to sustain a persistent infection. The mosquito-borne Venezuelan equine encephalitis virus (VEEV) belongs to the Togaviridae family and is an important biodefense pathogen and select agent. There are currently no approved vaccines or therapies for VEEV infections; therefore, it is imperative to identify novel targets for therapeutic development. We hypothesized that a functional UPS is required for efficient VEEV multiplication. We have shown that at non-toxic concentrations Bortezomib, a FDA-approved inhibitor of the proteasome, proved to be a potent inhibitor of VEEV multiplication in the human astrocytoma cell line U87MG. Bortezomib inhibited the virulent Trinidad donkey (TrD) strain and the attenuated TC-83 strain of VEEV. Additional studies with virulent strains of Eastern equine encephalitis virus (EEEV) and Western equine encephalitis virus (WEEV) demonstrated that Bortezomib is a broad spectrum inhibitor of the New World alphaviruses. Time-of-addition assays showed that Bortezomib was an effective inhibitor of viral multiplication even when the drug was introduced many hours post exposure to the virus. Mass spectrometry analyses indicated that the VEEV capsid protein is ubiquitinated in infected cells, which was validated by confocal microscopy and immunoprecipitation assays. Subsequent studies revealed that capsid is ubiquitinated on K48 during early stages of infection which was affected by Bortezomib treatment. This study will aid future investigations in identifying host proteins as potential broad spectrum therapeutic targets for treating alphavirus infections. 相似文献
8.
The plant‐specific protein FEHLSTART controls male meiotic entry,initializing meiotic synchronization in Arabidopsis 下载免费PDF全文
9.
C. ALBUQUERQUE F. MORINHA J. MAGALHÃES J. REQUICHA I. DIAS H. GUEDES-PINTO E. BASTOS C. VIEGAS 《Journal of genetics》2015,94(4):651-659
Elevated levels of interleukin-1 (IL-1) have been shown to amplify the inflammatory response against periodontopathogenic bacteria. In humans, polymorphisms in the IL1A and IL1B genes are the most well-studied genetic polymorphisms associated with periodontal disease (PD). In contrast to human, there is a lack of knowledge on the genetic basis of canine PD. A case–control study was conducted in which a molecular analysis of dog IL1A and IL1B genes was performed. Of the eight genetic variants identified, seven in IL1A gene and one in IL1B gene, IL1A/1_g.388A >C and IL1A/1_g.521T >A showed statistically significant differences between groups (adjusted OR (95% CI): 0.15 (0.03–0.76), P= 0.022; 5.76 (1.03–32.1), P= 0.046, respectively). It suggests that in the studied population the IL1A/1_g.388C allele is associated with a decreased PD risk, whereas the IL1A/1_g.521A allele can confer an increased risk. Additionally, the IL1A/2_g.515G >T variation resulted in a change of amino acid, i.e. glycine to valine. In silico analysis suggests that this change can alter protein structure and function, predicting it to be deleterious or damaging. This work suggests that IL1 genetic variants may be important in PD susceptibility in canines. 相似文献
10.
Mitch R. Lindquist Juan Carlos López-Núñez Marjorie A. Jones Elby J. Cox Rebecca J. Pinkelman Sookie S. Bang Bryan R. Moser Michael A. Jackson Loren B. Iten Cletus P. Kurtzman Kenneth M. Bischoff Siqing Liu Nasib Qureshi Kenneth Tasaki Joseph O. Rich Michael A. Cotta Badal C. Saha Stephen R. Hughes 《Applied microbiology and biotechnology》2015,99(22):9723-9743