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1.
2.
The ATP-binding-cassette transmembrane transporters (ABC transporters)
known from vertebrates belong to four major subfamilies: (1) the P-
glycoproteins (Pgp); (2) the cystic fibrosis transmembrane conductance
regulators (CFTR); (3) the Tap proteins encoded with the major
histocompatibility complex of mammals; and (4) the peroxisomal membrane
proteins. Both Pgp and CFTR have a structure suggesting a past internal
gene duplication; a phylogenetic analysis indicated that these duplications
occurred independently, while an independent tandem gene duplication
occurred in the case of the Tap family. Both the Pgp and Tap proteins show
evidence of relationship to bacterial ABC transporters lacking internal
duplication, and both are significantly more closely related to the HlyB
and MsbA families of transporters from purple bacteria than they are to ABC
transporters from nonpurple bacteria. The simplest hypothesis to explain
this observation is that eukaryotic Pgp and Tap genes are descended from a
mitochondrial gene or genes that were subsequently translocated to the
nuclear genome. The Pgp genes of eukaryotes are characterized by a
remarkable degree of convergent evolution between the ATP-binding cassettes
of their N- terminal and C-terminal halves, whereas no such convergence is
seen between the two halves of CFTR genes or between the duplicated Tap
genes. Exon 13 of the CFTR gene, which encodes a putative regulatory domain
not found in other ABC transporters apart from CFTR, showed high levels of
both synonymous and nonsynonymous difference in comparisons among different
mammalian species, suggesting that this region is a mutational hot spot.
相似文献
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X Xiao G Hintermann AL Demanin J Piret 《Journal of industrial microbiology & biotechnology》1996,16(4):261-262
Streptomyces glaucescens is shown to possess -lactamase activity which is inhibitable by clavulanate. This is important in regard to its use as a cloning host for enzymes of \-lactam biosynthesis. 相似文献
5.
Synthesis of L-2-oxothiazolidine-4-carboxylic acid 总被引:1,自引:0,他引:1
An improved synthesis of L-2- oxothiazolidine -4-carboxylic acid is described. The new procedure, which leads to excellent yields of product, does not require the use of phosgene. The new method is thus less hazardous than the original one, and is readily adaptable to the preparation of 35S-labeled product. 相似文献
6.
Biogeographic comparisons of marine algal polyphenolics: evidence against a latitudinal trend 总被引:5,自引:1,他引:4
Nancy M. Targett Loren D. Coen Anne A. Boettcher Christopher E. Tanner 《Oecologia》1992,89(4):464-470
Summary Marine allelochemicals generally are present in greater quantity and diversity in tropical than in temperate regions. Marine algal polyphenolics have been reported as an apparent exception to this biogeographic trend, with literature values for phenolic concentrations significantly higher in temperate than in tropical brown algae. In contrast, our results, the first reported for Caribbean brown algae (orders Dictyotales and Fucales), show that many species have high phenolic levels. In addition, both our study and previous studies with north temperate and tropical species demonstrate that there is marked variation in algal phenolic levels within species from different locations. We conclude that high phenolic concentrations occur in species from both temperate and tropical regions, indicating that latitude alone is not a reasonable predictor of plant phenolic concentrations. 相似文献
7.
The level of Fc receptor rosette-forming lymphocytes (Fc-RFL) was examined in spleen and lymph node cell suspension from neonatal DA and BN rats inoculated within 24 hr of birth with either allogeneic L (experimental) or syngeneic (control) lymphoid cells. In addition, these levels were compared to fetal and neonatal animals that received no injection. The indicator cells (EA) were sheep erythrocytes sensitized with one-half concentration of the highest dilution of rabbit anti-sheep erythrocyte IgG(A) which agglutinated an equal amount of 1% suspension of E. Care was taken to exclude scoring macrophages by injecting colloidal carbon at least 1 hr before killing the test animals. The spleen of 19-day DA fetal rats exhibited a level of 19.3% Fc-RFL, similar to that of animals having received adult syngeneic cells at birth (40.0%) by day 7. Thereafter the level of Fc-RFL did not vary appreciably between these two groups. However, as early as 2 days after inoculation there was a significantly greater number of Fc-RFL in the spleen of experimental DA neonates compared to controls. The lymph nodes of experimental animals did not exhibit a significantly greater number of Fc-RFL until day 6 with both tissue compartments peaking at day 10 and remaining significantly higher than controls until death. In neonatal BN animals significantly higher levels of Fc-RFL in experimental animals were not evident as early and peaked later (day 12) in both tissue compartments but again these differences remained until death. Cytotoxic alloantisera demonstrated that on days 6, 10, and 12 most, if not all, of the Fc-RFL were host in origion in both DA and BN GVHD, with a very significant host plasma cell response in such GVHD animals. One-micron tissue section revealed the presence of a great number of plasma cell especially prominent in the medulla of lymph nodes with the cortex of lymph nodes and white pulp of the spleen markedly depleted of lymphocytes indicative of cytotoxicity. 相似文献
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ERIC S. BONO PATRICK SMOLINSKI AL CASAGRANDA JUNDE XU 《Computer methods in biomechanics and biomedical engineering》2013,16(2):125-131
The Shear-slip Mesh Update Method (SSMUM) is being used in flow simulations involving large but regular displacements of one or more boundaries of the computational domain. We follow up the earlier discussion of the method with notes on practical implementation aspects. In order to establish a benchmark problem for this class of flow problems, we define and report results from a two-dimensional viscous flow around a rotating stirrer in a square chamber. The application potential of the method is demonstrated in the context of biomedical design problem, as we perform an analysis of blood flow in a centrifugal left ventricular assist device, or blood pump, which involves a rotating impeller in a non-axisymmetric housing. 相似文献
10.