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101.
102.
Monoclonal antibodies induce the translocation, patching, and shedding of surface antigens of sea urchin spermatozoa 总被引:2,自引:0,他引:2
Monoclonal antibodies reacting with external domains of plasma membrane proteins of sea urchin spermatozoa cause the reversible aggregation of sperm. The rate of disaggregation is temperature dependent indicating the involvement of membrane fluidity. Immunofluorescence shows that disaggregation is temporally correlated with the movement of surface-bound antibody into large aggregates which are then shed from the cell surface. Electrophoretic analysis of the shed antigens shows that they resemble the total complement of proteins of isolated sperm membranes. The translocation and shedding of surface-bound ligands may be a common property of eukaryotic flagellar membranes. 相似文献
103.
Biphasic Behavior of Anammox Regulated by Nitrite and Nitrate in an Estuarine Sediment 总被引:3,自引:1,他引:2
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Mark Trimmer Joanna C. Nicholls Nicholas Morley Christian A. Davies John Aldridge 《Applied microbiology》2005,71(4):1923-1930
The production of N2 gas via anammox was investigated in sediment slurries at in situ NO2− concentrations in the presence and absence of NO3−. With single enrichment above 10 μM 14NO2− or 14NO3− and 15NH4+, anammox activity was always linear (P < 0.05), in agreement with previous findings. In contrast, anammox exhibited a range of activity below 10 μM NO2− or NO3−, including an elevated response at lower concentrations. With 100 μM NO3−, no significant transient accumulation of NO2− could be measured, and the starting concentration of NO2− could therefore be regulated. With dual enrichment (1 to 20 μM NO2− plus 100 μM NO3−), there was a pronounced nonlinear response in anammox activity. Maximal activity occurred between 2 and 5 μM NO2−, but the amplitude of this peak varied across the study (November 2003 to June 2004). Anammox accounted for as much as 82% of the NO2− added at 1 μM in November 2003 but only for 15% in May 2004 and for 26 and 5% of the NO2− added at 5 μM for these two months, respectively. Decreasing the concentration of NO3− but holding NO2− at 5 μM decreased the significance of anammox as a sink for NO2−. The behavior of anammox was explored by use of a simple anammox-denitrification model, and the concept of a biphasic system for anammox in estuarine sediments is proposed. Overall, anammox is likely to be regulated by the availability of NO3− and NO2− and the relative size or activity of the anammox population. 相似文献
104.
Sacha AFT van Hijum Richard JS Baerends Aldert L Zomer Harma A Karsens Victoria Martin-Requena Oswaldo Trelles Jan Kok Oscar P Kuipers 《BMC bioinformatics》2008,9(1):1-10
Background
Visualising the evolutionary history of a set of sequences is a challenge for molecular phylogenetics. One approach is to use undirected graphs, such as median networks, to visualise phylogenies where reticulate relationships such as recombination or homoplasy are displayed as cycles. Median networks contain binary representations of sequences as nodes, with edges connecting those sequences differing at one character; hypothetical ancestral nodes are invoked to generate a connected network which contains all most parsimonious trees. Quasi-median networks are a generalisation of median networks which are not restricted to binary data, although phylogenetic information contained within the multistate positions can be lost during the preprocessing of data. Where the history of a set of samples contain frequent homoplasies or recombination events quasi-median networks will have a complex topology. Graph reduction or pruning methods have been used to reduce network complexity but some of these methods are inapplicable to datasets in which recombination has occurred and others are procedurally complex and/or result in disconnected networks.Results
We address the problems inherent in construction and reduction of quasi-median networks. We describe a novel method of generating quasi-median networks that uses all characters, both binary and multistate, without imposing an arbitrary ordering of the multistate partitions. We also describe a pruning mechanism which maintains at least one shortest path between observed sequences, displaying the underlying relations between all pairs of sequences while maintaining a connected graph.Conclusion
Application of this approach to 5S rDNA sequence data from sea beet produced a pruned network within which genetic isolation between populations by distance was evident, demonstrating the value of this approach for exploration of evolutionary relationships. 相似文献105.
JS Agerholm O Andersen MB Almskou C Bendixen J Arnbjerg GP Aamand US Nielsen F Panitz AH Petersen 《Acta veterinaria Scandinavica》2004,45(3):133
To investigate the congenital complex vertebral malformation syndrome (CVM) in Holstein calves, two breeding studies were
performed including 262 and 363 cows, respectively. Cows were selected from the Danish Cattle Database based on pedigree and
insemination records. Selected cows were progeny of sires with an established heterozygous CVM genotype and pregnant after
insemination with semen from another sire with heterozygous CVM genotype. Following calving the breeders should state, if
the calf was normal and was requested to submit dead calves for necropsy. In both studies, significantly fewer CVM affected
calves than expected were obtained; a finding probably reflecting extensive intrauterine mortality in CVM affected foetuses.
The findings illustrate increased intrauterine mortality as a major potential bias in observational studies of inherited disorders. 相似文献
106.
107.
Trimmer JK Casazza GA Horning MA Brooks GA 《American journal of physiology. Endocrinology and metabolism》2001,281(4):E683-E692
For estimating the oxidation rates (Rox) of glucose and other substrates by use of (13)C-labeled tracers, we obtained correction factors to account for label dilution in endogenous bicarbonate pools and TCA cycle exchange reactions. Fractional recoveries of (13)C label in respiratory gases were determined during 225 min of rest and 90 min of leg cycle ergometry at 45 and 65% peak oxygen uptake (VO(2 peak)) after continuous infusions of [1-(13)C]acetate, [2-(13)C]acetate, or NaH(13)CO(3). In parallel trials, [6,6-(2)H]glucose and [1-(13)C]glucose were given. Experiments were conducted after an overnight fast with exercise commencing 12 h after the last meal. During the transition from rest to exercise, CO(2) production increased (P < 0.05) in an intensity-dependent manner. Significant differences were observed in the fractional recoveries of (13)C label as (13)CO(2) at rest (NaH(13)CO(3), 77.5 +/- 2.8%; [1-(13)C]acetate, 49.8 +/- 2.4%; [2-(13)C]acetate, 26.1 +/- 1.4%). During exercise, fractional recoveries of (13)C label from [1-(13)C]acetate, [2-(13)C]acetate, and NaH(13)CO(3) were increased compared with rest. Magnitudes of label recoveries during both exercise intensities were tracer specific (NaH(13)CO(3), 93%; [1-(13)C]acetate, 80%; [2-(13)C]acetate, 65%). Use of an acetate-derived correction factor for estimating glucose oxidation resulted in Rox values in excess (P < 0.05) of glucose rate of disappearance during hard exercise. We conclude that, after an overnight fast: 1) recovery of (13)C label as (13)CO(2) from [(13)C]acetate is decreased compared with bicarbonate; 2) the position of (13)C acetate label affects carbon dilution estimations; 3) recovery of (13)C label increases in the transition from rest to exercise in an isotope-dependent manner; and 4) application of an acetate correction factor in glucose oxidation measurements results in oxidation rates in excess of glucose disappearance during exercise at 65% of VO(2 peak). Therefore, bicarbonate, not acetate, correction factors are advocated for estimating glucose oxidation from carbon tracers in exercising men. 相似文献
108.
Beta amyloid (Abeta) peptides accumulate in Alzheimer's disease and are neurotoxic possibly through the production of oxygen free radicals. Using brain microdialysis we characterized the ability of Abeta to increase oxygen radical production in vivo. The 1-40 Abeta fragment increased 2,3-dehydroxybenzoic acid efflux more than the 1-28 fragment, in a manner dependent on nitric oxide synthase and NMDA receptor channels. We then examined the effects of Abeta peptides on mitochondrial function in vitro. Induction of the mitochondrial permeability transition in isolated rat liver mitochondria by Abeta(25-35) and Abeta(35-25) exhibited dose dependency and required calcium and phosphate. Cyclosporin A prevented the transition as did ruthenium red, chlorpromazine, or N-ethylmaleimide. ADP and magnesium delayed the onset of mitochondrial permeability transition. Electron microscopy confirmed the presence of Abeta aggregates and swollen mitochondria and preservation of mitochondrial structure by inhibitors of mitochondrial permeability transition. Cytochrome c oxidase (COX) activity was selectively inhibited by Abeta(25-35) but not by Abeta(35-25). Neurotoxic Abeta peptide can increase oxidative stress in vivo through mechanisms involving NMDA receptors and nitric oxide sythase. Increased intracellular Abeta levels can further exacerbate the genetically driven complex IV defect in sporadic Alzheimer's disease and may precipitate mitochondrial permeability transition opening. In combination, our results provide potential mechanisms to support the feed-forward hypothesis of Abeta neurotoxicity. 相似文献
109.
Caspr2, a new member of the neurexin superfamily, is localized at the juxtaparanodes of myelinated axons and associates with K+ channels 总被引:9,自引:0,他引:9
Poliak S Gollan L Martinez R Custer A Einheber S Salzer JL Trimmer JS Shrager P Peles E 《Neuron》1999,24(4):1037-1047
Rapid conduction in myelinated axons depends on the generation of specialized subcellular domains to which different sets of ion channels are localized. Here, we describe the identification of Caspr2, a mammalian homolog of Drosophila Neurexin IV (Nrx-IV), and show that this neurexin-like protein and the closely related molecule Caspr/Paranodin demarcate distinct subdomains in myelinated axons. While contactin-associated protein (Caspr) is present at the paranodal junctions, Caspr2 is precisely colocalized with Shaker-like K+ channels in the juxtaparanodal region. We further show that Caspr2 specifically associates with Kv1.1, Kv1.2, and their Kvbeta2 subunit. This association involves the C-terminal sequence of Caspr2, which contains a putative PDZ binding site. These results suggest a role for Caspr family members in the local differentiation of the axon into distinct functional subdomains. 相似文献
110.
Glycosylation of ion channel proteins dramatically impacts channel function. Here we characterize the asparagine (N)-linked
glycosylation of voltage-gated K+ channel α subunits in rat brain and transfected cells. We find that in brain Kv1.1, Kv1.2 and Kv1.4, which have a single
consensus glycosylation site in the first extracellular interhelical domain, are N-glycosylated with sialic acid-rich oligosaccharide
chains. Kv2.1, which has a consensus site in the second extracellular interhelical domain, is not N-glycosylated. This pattern
of glycosylation is consistent between brain and transfected cells, providing compelling support for recent models relating
oligosaccharide addition to the location of sites on polytopic membrane proteins. The extent of processing of N-linked chains
on Kv1.1 and Kv1.2 but not Kv1.4 channels expressed in transfected cells differs from that seen for native brain channels,
reflecting the different efficiencies of transport of K+ channel polypeptides from the endoplasmic reticulum to the Golgi apparatus. These data show that addition of sialic acid-rich
N-linked oligosaccharide chains differs among highly related K+ channel α subunits, and given the established role of sialic acid in modulating channel function, provide evidence for differential
glycosylation contributing to diversity of K+ channel function in mammalian brain.
Received: 17 December 1998/Accepted: 20 January 1999 相似文献