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51.
52.
Bacterial lipopolysaccharides are recognized as the major cause of pyrogenic reactions from parenteral solutions. Molecular filtration was used to remove these pyrogenic molecules (endotoxins) from contaminated parenteral solutions. Because bacterial lipopolysaccharides can exist in different states of aggregation, depending on the composition of the solution they are suspended in, the full range of possible states of aggregation was examined by using filters with a wide range of pore sizes. Filters of different pore sizes retained endotoxin lipopolysaccharide presumed to be in the vesicle form, the micelle form, or the detergent-solubilized form in aqueous solutions. Endotoxins (pyrogens) were successfully removed from artificially contaminated solutions of concentrated antibiotics by using filters of 10,000-nominal-molecular-weight limit.  相似文献   
53.
Evolution of duplicate genes in a tetraploid animal, Xenopus laevis   总被引:6,自引:1,他引:5  
To understand the evolution of duplicate genes, we compared rates of nucleotide substitution between 17 pairs of nonallelic duplicated genes in the tetraploid frog Xenopus laevis with rates between the orthologous loci of human and rodent. For all duplicated X. laevis genes, the number of synonymous substitutions per site (dS) was greater than the number of nonsynonymous substitutions per site (dN), indicating that these genes are subject to purifying selection. There was also a significant positive correlation (r = 0.915) between dN for the X. laevis genes and dN for the mammalian genes, suggesting that, at the amino acid level, the X. laevis genes and the mammalian genes are under similar constraints. Results of relative-rate tests showed nearly equal rates of nonsynonymous substitution in each copy of the X. laevis genes; apparently there are similar constraints on both copies. No correlation was found between dS for the X. laevis genes and dS for the mammalian genes. There was a significant positive correlation both between members of pairs of duplicated X. laevis genes (r = 0.951) and between human and rodent orthologues (r = 0.854) with respect to third- position G+C content but no such relationship between the X. laevis genes and either of their mammalian orthologues. The results indicate that both copies of a duplicate gene can be subject to purifying selection and thus support the hypothesis of selection against all genotypes containing a null allele at either of two duplicate loci.   相似文献   
54.
Peroxisome proliferators, which induce proliferation of hepatic peroxisomes, have been shown previously to cause a marked increase in an 80,000 mol wt polypeptide predominantly in the light mitochondrial and microsomal fractions of liver of rodents. We now present evidence to show that this hepatic peroxisome-proliferation-associated polypeptide, referred to as polypeptide PPA-80, is immunochemically identical with the multifunctional peroxisome protein displaying heat-labile enoyl-CoA hydratase activity. This conclusion is based on the following observations: (a) the purified polypeptide PPA-80 and the heat- labile enoyl-CoA hydratase from livers of rats treated with the peroxisome proliferators Wy-14,643 {[4-chloro-6(2,3-xylidino)-2-pyrimidinylthio]acetic acid} exhibit identical minimum molecular weights of approximately 80,000 on SDS polyacrylamide gel electrophoresis; (b) these two proteins are immunochemically identical on the basis of ouchterlony double diffusion, immunotitration, rocket immunoelectrophoresis, and crossed immunoelectrophoresis analysis; and (c) the immunoprecipitates formed by antibodies to polypeptide PPA-80 when dissociated on a sephadex G-200 column yield enoyl-CoA hydratase activity. Whether the polypeptide PPA-80 exhibits the activity of other enzyme(s) of the peroxisomal β-oxidation system such as fatty acyl-CoA oxidase activity or displays immunochemical identity with such enzymes remains to be determined. The availability of antibodies to polypeptide PPA-80 and enoyl-CoA hydratase facilitated immunofluorescent and immunocytochemical localization of the polypeptide PPA- 80 and enoyl-CoA hydratase in the rat liver. The indirect immunofluorescent studies with these antibodies provided direct visual evidence for the marked induction of polypeptide PPA-80 and enoyl-CoA hydratase in the livers of rats treated with Wy-14,643. The present studies also provide immunocytochemical evidence for the localization of polypeptide PPA- 80 and the heat-labile enoyl-CoA hydratase in the peroxisome, but not in the mitochondria, of hepatic parenchymal cells. These studies, therefore, provide morphological evidence for the existence of fatty acyl-CoA oxidizing system in peroxisomes. An increase of polypeptide PPA-80 on SDS polyacrylamide gel electrophoretic analysis of the subcellular fractions of liver of rodents treated with lipid-lowering drugs should serve as a reliable and sensitive indicator of enhanced peroxisomal β- oxidation system.  相似文献   
55.
Bacterial lipopolysaccharides are recognized as the major cause of pyrogenic reactions from parenteral solutions. Molecular filtration was used to remove these pyrogenic molecules (endotoxins) from contaminated parenteral solutions. Because bacterial lipopolysaccharides can exist in different states of aggregation, depending on the composition of the solution they are suspended in, the full range of possible states of aggregation was examined by using filters with a wide range of pore sizes. Filters of different pore sizes retained endotoxin lipopolysaccharide presumed to be in the vesicle form, the micelle form, or the detergent-solubilized form in aqueous solutions. Endotoxins (pyrogens) were successfully removed from artificially contaminated solutions of concentrated antibiotics by using filters of 10,000-nominal-molecular-weight limit.  相似文献   
56.
Tetrahymena thermophila transforms from a pyriform-shaped trophic form to an elongate rapidly swimming, dispersal form under the appropriate conditions of starvation [Nelsen, E. M., and DeBault, L. E. (1978). J. Protozool.25, 113–119]. The development and control of the dispersal phenotype are examined. After an initial starvation period, the cell replaces its oral structures. During oral replacement, a caudal cilium emerges at the posterior end of the cell. As oral replacement is completed, the cell becomes spindle shaped and the newly-formed oral membranelles are positioned beneath the surface of the cell with somatic ciliary rows exterior to them. The spindle-shaped cell then elongates to become the dispersal form. While the cell is developing the new oral structures, it is also drastically increasing its numbers of somatic basal bodies and cilia. The events in the transformation pathway may be arrested or reversed by feeding the cell, except that once oral replacement has begun, it is completed along with an associated streamlining of the cell. Refed cells revert to the normal vegetative phenotype, except that some shape changes persist for several hours, suggesting that they are compatible with, but independent of, growth. Blockage of protein synthesis with cycloheximide prevents all changes associated with transformation, including the shape changes and elongation of the caudal cilium. The relation between transformation and conjugation has also been examined. Less transformation takes place when mating is possible, but transformed cells may also mate.  相似文献   
57.
58.
The lymphocyte-specific immunoglobulin mu heavy-chain gene intronic enhancer is regulated by multiple nuclear factors. The previously defined minimal enhancer containing the muA, muE3, and muB sites is transactivated by a combination of the ETS-domain proteins PU.1 and Ets-1 in nonlymphoid cells. The core GGAAs of the muA and muB sites are separated by 30 nucleotides, suggesting that ETS proteins bind to these sites from these same side of the DNA helix. We tested the necessity for appropriate spatial alignment of these elements by using mutated enhancers with altered spacings. A 4- or 10-bp insertion between muE3 and muB inactivated the mu enhancer in S194 plasma cells but did not affect in vitro binding of Ets-1, PU.1, or the muE3-binding protein TFE3, alone or in pairwise combinations. Circular permutation and phasing analyses demonstrated that PU.1 binding but not TFE3 or Ets-1 bends mu enhancer DNA toward the major groove. We propose that the requirement for precise spacing of the muA and muB elements is due in part to a directed DNA bend induced by PU.1.  相似文献   
59.
We describe a new scaffold-free three-dimensional (3D) cell culture model using cholesteryl ester based lyotropic liquid crystal (LC) substrates. Keratinocytes were deposited randomly on the LC surface where they self-assembled into 3D microtissues or keratinospheroids. The cell density required to form spheroids was optimized. We investigated cell viability using dead/live cell assays. The adhesion characteristics of cells within the microtissues were determined using histological sectioning and immunofluorescence staining. Fourier transform infrared spectroscopy (FTIR) was used to characterize the biochemistry of the keratinospheroids. We found that both cells and microtissues could migrate on the LC surface. The viability study indicated approximately 80% viability of cells in the microtissues up to 20 days of culture. Strong intercellular adhesion was observed in the stratification of the multi-layered microspheroids using field emission-scanning electron microscopy (FE-SEM) and histochemical staining. The cytoskeleton and vinculins of the cells in the microtissues were expressed diffusely, but the microtissues were enriched with lipids and nucleic acids, which indicates close resemblance to the conditions in vivo. The basic 3D culture model based on LC may be used for cell and microtissue migration studies in response to cytochemical treatment.  相似文献   
60.
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