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排序方式: 共有156条查询结果,搜索用时 15 毫秒
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Litman GW; Rast JP; Shamblott MJ; Haire RN; Hulst M; Roess W; Litman RT; Hinds- Frey KR; Zilch A; Amemiya CT 《Molecular biology and evolution》1993,10(1):60-72
Immunoglobulins are encoded by a large multigene system that undergoes
somatic rearrangement and additional genetic change during the development
of immunoglobulin-producing cells. Inducible antibody and antibody-like
responses are found in all vertebrates. However, immunoglobulin possessing
disulfide-bonded heavy and light chains and domain-type organization has
been described only in representatives of the jawed vertebrates. High
degrees of nucleotide and predicted amino acid sequence identity are
evident when the segmental elements that constitute the immunoglobulin gene
loci in phylogenetically divergent vertebrates are compared. However, the
organization of gene loci and the manner in which the independent elements
recombine (and diversify) vary markedly among different taxa. One striking
pattern of gene organization is the "cluster type" that appears to be
restricted to the chondrichthyes (cartilaginous fishes) and limits
segmental rearrangement to closely linked elements. This type of gene
organization is associated with both heavy- and light-chain gene loci. In
some cases, the clusters are "joined" or "partially joined" in the germ
line, in effect predetermining or partially predetermining, respectively,
the encoded specificities (the assumption being that these are expressed)
of the individual loci. By relating the sequences of transcribed gene
products to their respective germ-line genes, it is evident that, in some
cases, joined-type genes are expressed. This raises a question about the
existence and/or nature of allelic exclusion in these species. The
extensive variation in gene organization found throughout the vertebrate
species may relate directly to the role of intersegmental
(V<==>D<==>J) distances in the commitment of the individual
antibody-producing cell to a particular genetic specificity. Thus, the
evolution of this locus, perhaps more so than that of others, may reflect
the interrelationships between genetic organization and function.
相似文献
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Perfusion with [8-14C]adenosine demonstrated the likely existence in rat liver of oligophosphoglyceroyl-ATP (OPG-ATP). Purification followed by assay with a new specific 3' phosphodiesterase confirmed this. The quantities present were 5-10-fold those found previously and comparable to total soluble nucleotides. OPG-ATP was also purified from the mitochondrial fraction, shown to co-distribute with succinate dehydrogenase and can be co-purified with an enzyme confined to intermembrane space. 相似文献
5.
R Keays P M Harrison J A Wendon A Forbes C Gove G J Alexander R Williams 《BMJ (Clinical research ed.)》1991,303(6809):1026-1029
OBJECTIVE--To see whether intravenous acetylcysteine would improve outcome in patients with fulminant hepatic failure after paracetamol overdose. DESIGN--A prospective randomised controlled study. SETTING--The Institute of Liver Studies, King''s College Hospital, London. PATIENTS--50 consecutive patients (21 male) aged 16-60 with fulminant hepatic failure after paracetamol overdose who had not previously received acetylcysteine. INTERVENTIONS--Conventional intensive liver care plus either acetylcysteine (25 patients) in the same dose regimen as used early after a paracetamol overdose, except that the infusion was continued until recovery from encephalopathy or death, or an equivalent volume of 5% dextrose (25 patients). MAIN OUTCOME MEASURES--Survival; incidence of cerebral oedema, renal failure, and hypotension requiring inotropic support; liver function as assessed by prolongation of the prothrombin time; and degree of encephalopathy. RESULTS--The rate of survival was significantly higher in the acetylcysteine treated group than in the controls (48% (12/25 patients) v 20% (5/25); p = 0.037, 95% confidence interval for difference in proportions surviving 3% to 53%). Acetylcysteine treated patients had a lower incidence of cerebral oedema (40% (10/25) v 68% (17/25); p = 0.047, 95% confidence interval for difference in incidence 2% to 54%), and fewer developed hypotension requiring inotropic support (48% (12/25) v 80% (20/25); p = 0.018, 95% confidence interval 7% to 57%). Rates of deterioration and recovery of liver function, however, were similar in the two groups. No adverse reactions to acetylcysteine were seen. CONCLUSIONS--Acetylcysteine is safe and effective in fulminant hepatic failure after paracetamol overdose. 相似文献
6.
The isozymic similarity of indoleacetic Acid oxidase to peroxidase in birch and horseradish 总被引:2,自引:1,他引:1
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The relationship of indoleacetic acid oxidase activity to peroxidase activity is complicated by numerous multiple forms of this enzyme system. It is not known if all isozymes of this complex system contain both types of activity. Isozyme analysis of commercial horseradish peroxidase and leaf extracts of yellow birch (Betula alleghaniensis) by isoelectric focusing in polyacrylamide gels was used to examine this problem. Horseradish and birch exhibited 20 and 13 peroxidase isozymes, respectively, by staining with benzidine or scopoletin. Guaiacol was less sensitive. Indoleacetic acid oxidase staining (dimethylaminocinnamaldehyde) generally showed fewer bands, and left doubt as to the residence of both types of activity on all isozymes. Elution of the isozymes from the gels and wet assays verified that all peroxidase isozymes contained indoleacetic acid oxidase activity as well. Estimation of oxidase to peroxidase ratios for the major bands indicated small differences in this parameter. A unique isozyme for one or the other type of activity was not found. 相似文献
7.
Jamison M. Gove Gareth J. Williams Margaret A. McManus Scott F. Heron Stuart A. Sandin Oliver J. Vetter David G. Foley 《PloS one》2013,8(4)
Coral reef ecosystems are exposed to a range of environmental forcings that vary on daily to decadal time scales and across spatial scales spanning from reefs to archipelagos. Environmental variability is a major determinant of reef ecosystem structure and function, including coral reef extent and growth rates, and the abundance, diversity, and morphology of reef organisms. Proper characterization of environmental forcings on coral reef ecosystems is critical if we are to understand the dynamics and implications of abiotic–biotic interactions on reef ecosystems. This study combines high-resolution bathymetric information with remotely sensed sea surface temperature, chlorophyll-a and irradiance data, and modeled wave data to quantify environmental forcings on coral reefs. We present a methodological approach to develop spatially constrained, island- and atoll-scale metrics that quantify climatological range limits and anomalous environmental forcings across U.S. Pacific coral reef ecosystems. Our results indicate considerable spatial heterogeneity in climatological ranges and anomalies across 41 islands and atolls, with emergent spatial patterns specific to each environmental forcing. For example, wave energy was greatest at northern latitudes and generally decreased with latitude. In contrast, chlorophyll-a was greatest at reef ecosystems proximate to the equator and northern-most locations, showing little synchrony with latitude. In addition, we find that the reef ecosystems with the highest chlorophyll-a concentrations; Jarvis, Howland, Baker, Palmyra and Kingman are each uninhabited and are characterized by high hard coral cover and large numbers of predatory fishes. Finally, we find that scaling environmental data to the spatial footprint of individual islands and atolls is more likely to capture local environmental forcings, as chlorophyll-a concentrations decreased at relatively short distances (>7 km) from 85% of our study locations. These metrics will help identify reef ecosystems most exposed to environmental stress as well as systems that may be more resistant or resilient to future climate change. 相似文献
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Background
In addition to known protein-coding genes, large amounts of apparently non-coding sequence are conserved between the human and mouse genomes. It seems reasonable to assume that these conserved regions are more likely to contain functional elements than less-conserved portions of the genome. 相似文献10.