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61.
The production of siderophores by four Streptomyces strains, S. ambofaciens, S. coelicolor, S. lividans, and S. viridosporus, was studied under iron-limited conditions. S. viridosporus produced two different siderophores: the linear desferrioxamine B and the cyclic desferrioxamine E. The latter was produced by the other strains and was the main siderophore of S. ambofaciens. The linear desferrioxamine G was the major form of S. coelicolor and S. lividans. The uptake rates of 55Fe-labeled ferrioxamines by S. lividans and S. viridosporus showed that the G form was incorporated less efficiently than the B and E forms. 相似文献
62.
Astrocytes are the primary site of glutamate conversion to glutamine in the brain. We examined the effects of treatment with either dibutyryl cyclic AMP and/or the synthetic glucocorticoid dexamethasone on glutamine synthetase enzyme activity and steady-state mRNA levels in cultured neonatal rat astrocytes. Treatment of cultures with dibutyryl cyclic AMP alone (0.25 mM–1.0 mM) increased glutamine synthetase activity and steady state mRNA levels in a dose-dependent manner. Similarly, treatment with dexamethasone alone (10–7–10–5 M) increased glutamine synthetase mRNA levels and enzyme activity. When astrocytes were treated with both effectors, additive increases in glutamine synthetase activity and mRNA were obtained. However, the additive effects were observed only when the effect of dibutyryl cyclic AMP alone was not maximal. These findings suggest that the actions of these effectors are mediated at the level of mRNA accumulation. The induction of glutamine synthetase mRNA by dibutyryl cyclic AMP was dependent on protein synthesis while the dexamethasone effect was not. Glucocorticoids and cyclic AMP are known to exert their effects on gene expression by different molecular mechanisms. Possible crosstalk between these effector pathways may occur in regulation of astrocyte glutamine synthetase expression.Abbreviations used GS
glutamine synthetase
- dbcAMP
dibutyryl cyclic AMP
- MEM
minimal essential medium
- cyx
cycloheximide
- GRE
glucocorticoid response element
- CRE
cyclic AMP response element 相似文献
63.
Maninder K. Sohi Tommy Wan Brian J. Sutton Tony Atkinson Max A. Atkinson Jonathan P. Murphy Stephen P. Bottomley Michael G. Gore 《Proteins》1995,23(4):610-612
Protein L is a multi domain cell wall constituent of certain strains of Peptostreptococcus magnus which binds to the variable domain of immunoglobulin κ-light chains. A single immunoglobulin-binding domain of Mr = 9000 from this protein has been isolated and crystallized. The crystals are of space group P42212, with cell dimensions a = b = 66.9 Å, c = 68.3 Å, and diffract to at least 2.2 Å resolution. The asymmetric unit of the crystal contains two molecules of the protein L domain, related by a noncrystallographic 2-fold axis, as revealed by a self-rotation function calculated with native diffraction data. © 1995 Wiley-Liss, Inc. 相似文献
64.
Sara S. Tynan Niels H. Andersen Max T. Wills Laurence A. Harker Stephen R. Hanson 《Prostaglandins & other lipid mediators》1984,27(5):683-696
The ω-chain variant analogs of prostacyclin (PGI2) and PGD2 in which the n-amyl side-chain has been replaced by a cyclohexyl group have been prepared and their cardiovascular activities have been compared to those of BW-245C(Fig. 1)(1) a potent anti-aggregatory vasodilator bearing a cyclohexyl-terminated side-chain on a hydantoin skeleton. The cyclohexyl group has little effect on PGI2, but converts PGD2 to a long lasting hypotensive agent and increases the platelet anti-aggregatory potency of PGD2 by a factor of 8. The prostaglandin antagonist N-0164 selectively blocks the anti-aggregatory actions of PGD2, cyclohexyl-PGD2, and BW-245C; with essentially no effect on PGI2, cyclohexyl-PGI2 and PGE2 at comparably effective doses. The latter observation is contrary to an earlier report by MacIntyre (2,3), but supports the view that the anti-aggregatory effect of high doses of PGE2 () is mediated by the PGI2 receptor (4). The hydantoin acts at the platelet PGD2 receptor. 相似文献
65.
66.
Max R. Taylor Lucy A. Lawson Virginia G. Lockard William R. Lockwood 《Mycopathologia》1984,88(2-3):173-180
Electron microscopic examination of yeasts of Blastomyces dermatitidis, exposed in vitro to concentrations of lidocaine that occur when the drug is used for topical anesthesia, showed that lidocaine rapidly damaged intracellular structures. The extent of damage was dependent on the concentration of drug and length of exposure. The observed ultrastructural changes were very similar to those reported for other drugs that directly damage membranes. This relationship suggests that the antifungal effect of lidocaine is the result of direct membrane damage. 相似文献
67.
In the DNA of higher vertebrates the dinucleotide CG is unique in two respects: it occurs far less frequently than would be expected on the basis of the content of cytosine and guanine in a given DNA segment ("CG suppression") and it contains predominantly 5-methyl-cytosine, the only modified nucleotide common in vertebrate DNA. Here we point out the existence of CG clusters, i.e. localized lapses in the usual CG suppression, in two categories of DNA segments from vertebrates: around the polymorphic exons of major histocompatibility complex (MHC) genes and in the 5' regions of certain other genes. These observations contradict the recent suggestion that CG frequency is uniform over long contiguous segments of DNA containing several genes. A model for the origin of these CG clusters as a consequence of regional demethylation of germline DNA is supported by analysis of other sequence features of these regions as well as by previously published data on the methylation status in sperm DNA of two of these CG-rich regions. 相似文献
68.
69.
Donald L. Ewert Douglas G. Gilmour W. Elwood Briles Max D. Cooper 《Immunogenetics》1980,10(1-4):169-174
Two sets of backcross matings were performed to test for linkage between genes coding for the Ia-like antigens (Ia) and the B erythrocyte antigens (Ea-B) of the chicken. Evidence is presented which indicates that the la antigens are determined by a single codominant locus and that theEa-B and Ia loci are on the same chromosome. Failure to detect a single recombinant between theEa-B and Ia loci out of 208 progeny suggests close linkage of the two genes with a map distance of up to about 2 centimorgans. The Ia genes are thus included in theB major histocompatibility complex of the chicken. 相似文献
70.
Biology of Azospirillum-Sugarcane Association: Enhancement of Nitrogenase Activity 总被引:4,自引:2,他引:2
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R. Howard Berg Max E. Tyler Norman J. Novick Vimla Vasil Indra K. Vasil 《Applied microbiology》1980,39(3):642-649
Azospirillum brasilense was reisolated from associations with callus tissue cultures of sugarcane and compared with stock cultures of the inoculated bacterium and related strains. Although the reisolate had a growth rate similar to stock cultures, it exhibited a severalfold increase in maximum specific activity of nitrogenase. The reisolate and the parent culture had similar ultrastructure. The general ultrastructure of Azospirillum is described. The bacterium was capsulated when grown on nitrogen-free nutrient agar plates and on callus, but was not capsulated when growing in a subsurface zone in N-free semisolid nutrient agar, except rarely in aging cultures. Capsulation may be a protective mechanism against unfavorable pO2 under dinitrogen-fixing conditions. Pleomorphism occurred in capsulated forms, and the ultrastructure of these forms is described. 相似文献