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91.
The oligomerization of a family of four genetically clustered human gastrointestinal mucins 总被引:1,自引:0,他引:1
Mucins are synthesized and secreted by many epithelia. They are complex
glycoproteins that offer cytoprotection. In their functional configuration,
mucins form oligomers by a biosynthetic process that is poorly understood.
A family of four human gastrointestinal mucin genes (MUC2, MUC5AC, MUC5B,
and MUC6) is clustered to chromosome 11p15.5. To study oligomerization of
these related mucins, we performed metabolic labeling experiments with
[35S]amino acids in LS174T cells, and isolated mucin precursors by specific
immunoprecipitations that were analyzed on SDS-PAGE. Each of the precursors
of MUC2, MUC5AC, MUC5B, and MUC6 formed a single species of
disulfide-linked homo-oligomer within 1 h after pulse labeling. Based on
apparent molecular masses, these oligomeric precursors were most likely
dimers. Inhibition of vesicular RER-to-Golgi transport, with brefeldin A
and CCCP, did not affect the dimerization of MUC2 precursors, localizing
dimerization to the RER. O-Glycosylation of MUC2 followed dimerization.
Inhibition of N- glycosylation by tunicamycin retarded, but did not
inhibit, dimerization, indicating that N-glycans play a role in efficient
dimerization of MUC2 precursors. Based on sequence homology, the ability of
MUC2, MUC5AC, MUC5B and MUC6 to dimerize most likely resides in their
C-terminal domains. Thus, the RER-localized dimerization of secretory
mucins likely proceeds by similar mechanisms, which is an essential step in
the formation of the human gastrointestinal mucus- gels.
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92.
1. Considerable evidence suggests that the diversity within plant communities may strongly affect the strength of species interactions, but the majority of studies only considered interspecific diversity. 2. This paper examines the effect of intraspecific genetic diversity within Brassica fields on two Brassica specialists, cabbage root fly, and diamondback moth, and on a parasitoid attacking diamondback moths. Genetic diversity was manipulated both in a replacement and an additive design. 3. Both herbivore densities and parasitism rates were higher in smaller plots, with limited responses to increased within‐plot diversity. All species showed variable densities across genotypes, and preference hierarchies were species specific. 4. Responses to plot size in root flies scaled with the diameter‐to‐area ratio, suggesting that patch detectability affected local density, whereas responses by diamondback moths and parasitoids deviated from this ratio. These species differences could be traced to differences in the residence time within patches, where diamondback moths typically spend longer and more variable time periods in patches than root flies. 5. The lack of response to genetic diversity by both herbivores suggests that egg‐laying rates are affected by decisions on the plant and not by attraction from a distance, neither to the plant itself nor the patch. Patterns of differential attack may then be due to different acceptability for studied genotypes. 6. Future theories on insect responses to spatial heterogeneity should focus on species traits and how traits interact with information landscapes in the field. 相似文献
93.
NELSON VALDIVIA JARROD D. STEHBENS BJÖRN HERMELINK SEAN D. CONNELL MARKUS MOLIS MARTIN WAHL 《Austral ecology》2008,33(8):951-962
Local dynamics such as resource enhancement (e.g. nutrient supply) and stochastic events of destruction (disturbances that provide new space) are hypothesized to counteractively affect species diversity and composition. We tested the independent and interactive effects of nutrients and disturbance on the development of assemblages of epibiota attached to vertical surfaces in an oligotrophic system. Nutrient concentrations were manipulated at three levels (ambient, medium and high) while disturbance was manipulated by removing biomass at seven frequencies (0×, 2×, 3×, 4×, 5×, 7×, 12×). Nutrient and disturbance regimes had opposing effects on diversity such that species richness increased with resource enhancement (nutrients) and declined with disturbance. These results support the model that increased heterogeneity of distribution of limiting resources allows the coexistence of species with low and high resource requirements. 相似文献
94.
Picha J Kuca K Kivala M Kohout M Cabal J Liska F 《Journal of enzyme inhibition and medicinal chemistry》2005,20(3):233-237
Reactivators of acetylcholinesterase (AChE; EC 3.1.1.7) are able to treat intoxication by organophosphorus compounds, especially with pesticides or nerve agents. Owing to the fact that there exists no universal "broad-spectrum" reactivator of organophosphates-inhibited AChE, many laboratories have synthesized new AChE reactivators. Here, we synthesized five new and three previously known quaternary monopyridinium oximes as potential reactivators of AChE inhibited by nerve agents. Potencies to cleave p-nitrophenyl acetate (PNPA), which is commonly used as a model substrate of nerve agents, were measured. Their cleaving potencies were compared with 4-PAM (4-hydroxyiminomethyl-1-methylpyridinium iodide), which is derived from the structure of the currently used AChE-reactivator 2-PAM (2-hydroxyiminomethyl-1-methylpyridinium iodide). Three newly synthesized oximes achieved similar nucleophilicity at the similar pKa according to 4-PAM, which is very promising for using these derivatives as AChE reactivators. 相似文献
95.
Abstract The palatability to common carp, Cyprinus carpio L. of three newly developed differently flavoured floating pellets made from a high proportion (40%) of brewer's spent grain (BSG) was tested using a multiple-offer feeding experiment. The addition of ‘bold’ flavours, such as vanilla or strawberry essence, may help mask the unpleasant taste of some piscicides; however, their inclusion must not compromise uptake by carp. There were no significant differences between the consumption rates of the three varieties, and all flavours were readily consumed. Therefore, it is suggested that highly flavoured pellets made with BSG have a strong potential to mask the flavour of an unpalatable toxin, and further research is now needed to test this hypothesis. 相似文献
96.
Cardiac outflow of amino acids and purines during myocardial ischemia and reperfusion. 总被引:2,自引:0,他引:2
Tobias B?ckstr?m Michel Goiny Ulf Lockowandt Jan Liska Anders Franco-Cereceda 《Journal of applied physiology》2003,94(3):1122-1128
A novel application of microdialysis was studied, in which myocardial outflow of amino acids and purines was monitored by intravasal microdialysis in the myocardial venous outflow during ischemia and reperfusion. Microdialysis catheters were introduced into the great cardiac vein, pulmonary artery, and external jugular vein in 20 anesthetized pigs. The left anterior descending artery was occluded in four groups of pigs for 0, 10, 15, and 60 min. Ischemia was followed by 120 min of reperfusion. Microdialysis samples were analyzed for taurine, aspartate, glutamate, hypoxanthine, inosine, and guanosine. Myocardial infarction developed when ischemia exceeded 10 min. Taurine, aspartate, inosine, and guanosine increased early in the great cardiac vein during ischemia. We found the outflow patterns of amino acids and purines to be graded in response to different lengths of ischemia. In this study we have demonstrated a graded outflow of amino acids and purines in response to ischemia and a positive correlation between infarct size and myocardial outflow of amino acids and purines. This could be of value in a clinical setting to quantify the extent of myocardial damage. 相似文献
97.
The MultiTag method (Sunyaev et al., Anal. Chem. 2003 15, 1307-1315) employs multiple error-tolerant searches with peptide sequence tags (Mann and Wilm, Anal. Chem. 1994, 66, 4390-4399) for the identification of proteins from organisms with unsequenced genomes. Here we demonstrate that the error-tolerant capabilities of MultiTag increased the number of peptide alignments and improved the confidence of identifications in an EST database. The MultiTag outperformed conventional database searching software that only utilizes stringent matching of tandem mass spectra to nucleotide sequences of ESTs. 相似文献
98.
99.
100.
Previous studies of the effect of carbonation on taste perception have
suggested that it may be negligible, manifesting primarily in increases in
the perceived intensity of weak salt and sour stimuli. Assuming CO2
solutions in the mouth stimulate only trigeminal nerve endings, this result
is not altogether surprising; however, there are neurophysiological data
indicating that CO2 stimulates gustatory as well as trigeminal fibers. In
that case, carbonation might alter the quality profile of a stimulus
without producing substantial changes in overall taste intensity--much as
occurs when qualitatively different taste stimuli are mixed. To address
this possibility, subjects were asked to rate the total taste intensity of
moderate concentrations of stimuli representing each of the basic tastes
and their binary combinations, with an without added carbonation. They then
subdivided total taste intensity into the proportions of sweetness,
saltiness, sourness, bitterness and 'other taste qualities' they perceived.
The addition of carbonation produced only small increases in ratings of
total taste intensity. However, rather dramatic alterations in the quality
profiles of stimuli were observed, particularly for sweet and salty tastes.
The nature of the interaction is consistent with a direct effect of
carbonation/CO2 on the gustatory system, although the possibility that at
least some of the observed effects reflect trigeminal-gustatory
interactions cannot be ruled out.
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