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1.
Molecular analysis of a beta-lactam resistance gene encoded within the cephamycin gene cluster of Streptomyces clavuligerus.
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A Streptomyces clavuligerus gene (designated pcbR) which is located immediately downstream from the gene encoding isopenicillin N synthase in the cephamycin gene cluster was characterized. Nucleotide sequence analysis and database searching of PcbR identified a significant similarity between PcbR and proteins belonging to the family of high-molecular-weight group B penicillin-binding proteins (PBPs). Eight of nine boxes (motifs) conserved within this family of proteins are present in the PcbR protein sequence in the same order and with approximately the same spacing between them. When a mutant disrupted in pcbR was constructed by gene replacement, the resulting pcbR mutant exhibited a significant decrease in its resistance to benzylpenicillin and cephalosporins, indicating that pcbR is involved in beta-lactam resistance in this organism. Western blot (immunoblot) analysis of S. clavuligerus cell membranes using PcbR-specific antibodies suggested that PcbR is a membrane protein. PcbR was also present in cell membranes when expressed in Escherichia coli and was able to bind radioactive penicillin in a PBP assay, suggesting that PcbR is a PBP. When genomic DNAs from several actinomycetes were probed with pcbR, hybridization was observed to some but not all beta-lactam-producing actinomycetes. 相似文献
2.
Differential response of cycling and noncycling cells to inducers of DNA synthesis and mitosis 总被引:1,自引:0,他引:1
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The objective of this study was to determine whether cells in G(0) phase are functionally distinct from those in G(1) with regard to their ability to respond to the inducers of DNA synthesis and to retard the cell cycle traverse of the G(2) component after fusion. Synchronized populations of HeLa cells in G(1) and human diploid fibroblasts in G(1) and G(0) phases were separately fused using UV-inactivated Sendai virus with HeLa cells prelabeled with [(3)H]ThdR and synchronized in S or G(2) phases. The kinetics of initiation of DNA synthesis in the nuclei of G(0) and G(1) cells residing in G(0)/S and G(1)/S dikaryons, respectively, were studied as a function of time after fusion. In the G(0)/G(2) and G(1)/G(2) fusions, the rate of entry into mitosis of the heterophasic binucleate cells was monitored in the presence of Colcemid. The effects of protein synthesis inhibition in the G(1) cells, and the UV irradiation of G(0) cells before fusion, on the rate of entry of the G(2) component into mitosis were also studied. The results of this study indicate that DNA synthesis can be induced in G(0)nuclei after fusion between G(0)- and S-phase cells, but G(0) nuclei are much slower than G(1) nuclei in responding to the inducers of DNA synthesis because the chromatin of G(0) cells is more condensed than it is in G(1) cells. A more interesting observation resulting from this study is that G(0) cells is more condensed than it is in G(1) cells. A more interesting observation resulting from this study is that G(0) cells differ from G(1) cells with regard to their effects on the cell cycle progression of the G(2) nucleus into mitosis. This difference between G(0) and G(1) cells appears to depend on certain factors, probably nonhistone proteins, present in G(1) cells but absent in G(0) cells. These factors can be induced in G(0) cells by UV irradiation and inhibited in G(1) cells by cycloheximide treatment. 相似文献
3.
The purpose of this study was to formulate a gelled self-emulsifying drug delivery system (SEDDS) containing ketoprofen as
an intermediate in the development of sustained release solid dosage form. Captex 200 (an oil), Tween 80 (a surfactant), and
Capmul MCM (a cosurfactant) were used to formulate SEDDS. Silicon dioxide was used as a gelling agent, which may aid in solidification
and retardation of drug release. Effect of concentrations of cosurfactant and gelling agent on emulsification process and
in vitro drug diffusion was studied using 32 factorial design. Multiple regression analysis data and response surfaces obtained showed that liquid crystal phase viscosity
increased significantly with increasing amount of silicon dioxide, which in turn caused an increase in average droplet size
of resultant emulsion and slower drug diffusion. Drug release from the formulation increased with increasing amount of cosurfactant. 相似文献
4.
The purpose of this research was to obtain directly compressible agglomerates of ibuprofen-paracetamol containing a desired
ratio of drugs using a crystallo-co-agglomeration technique. Crystallo-co-agglomeration is an extension of the spherical crystallization
technique, which enables simultaneous crystallization and agglomeration of 2 or more drugs or crystallization of a drug and
its simultaneous agglomeration with another drug or excipient. Dichloromethane (DCM)-water system containing polyethylene
glycol (PEG) 6000, polyvinyl pyrollidone, and ethylcellulose was used as the crystallization system. DCM acted as a good solvent
for ibuprofen and bridging liquid for agglomeration. The process was performed at pH 5, considering the low solubility of
ibuprofen and the stability of paracetamol. Loss of paracetamol was reduced by maintaining a low process temperature and by
the addition of dextrose as a solubility suppressant. The agglomerates were characterized by differential scanning calorimetry,
powder x-ray diffraction (PXRD), and scanning electron microscopy and were evaluated for tableting properties. The spherical
agglomerates contained an ibuprofen-paracetamol ratio in the range of 1.23 to 1.36. Micromeritic, mechanical, and compressional
properties of the agglomerates were affected by incorporated polymer. The PXRD data showed reduction in intensities owing
to dilution and reduced crystallinity. Thermal data showed interaction between components at higher temperature. Ethylcellulose
imparted mechanical strength to the agglomerates as well as compacts. The agglomerates containing PEG have better comparessibility
but drug release in the initial stages was affected owing to asperity melting, yielding harder compacts. The agglomeration
and properties of agglomerates were influenced by the nature of polymer. 相似文献
5.
Conclusion Hydrolyzed gelatins (Byco-A, Byco-O and Byco-C), when used as binders, yielded soft, uniform granules with good flow properties.
As the molecular weight and viscosity of hydrolyzed gelatins increased, the compressibility of granules decreased and their
compactability increased. The balance between compressibility and compactability of granules may be achieved by careful monitoring
of the molecular weight of hydrolyzed gelatins that can serve as potential binders. 相似文献
6.
Amelt solidification technique has been developed to obtain sustained-release waxy beads of flurbiprofen. Low glass transition
temperature (t
g) and shear-induced crystallization of flurbiprofen made it a suitable candidate for melt solidification technique. The process
involved emulsification and solidification of flurbiprofen-cetyl alcohol melt at significantly low temperature (5°C). The
effect of variables, namely, the amount of cetyl alcohol and the speed of agitation, was studied using 32 factorial design. The technique and the beads were evaluated on the basis of process and desired yield, surface topography,
Fourier-transform infrared (FT-IR), differential scanning calorimetry (DSC), particle size distribution, crushing strength,
and drug release. Average values for process and desired yields were 97% wt/wt and 26% wt/wt, respectively. No interaction
was observed between drug and excipient. Multiple regression analysis was carried out, and response surfaces were obtained.
A curvilinear relationship was observed between percentage of desired yield and the amount of cetyl alcohol. Linear decrease
in crushing strength was observed with increase in the amount of cetyl alcohol. Drug released from the beads followed zero
order kinetics. Burst release was shown to a greater extent in beads containing a lower amount of cetyl alcohol. Response
surfaces of time required for certain percentage of drug (t
D%) showed that after critical concentration of about 20% of cetyl alcohol (400 mg/batch), no significant release retardant
effect was observed. 相似文献
7.
温室条件下,用0(Control)、8.65kJm-2d-1(TI)及11.2KJm-2d-1(t2)不同剂量的UV-B辐射处理蚕豆幼苗。Ca2 .ATPase及Mg2 -ATPase的活性在辐射处理期间下降。在处理21d,T1和T2微粒体膜的MDA含量明显高于对照,同时IUFA急剧下降,且呈明显的剂量效应。14及21d时,膜磷脂的含量也明显下降。脂氧合酶(Lox)活性在第7及14天与对照相比都显著升高,而21d后迅速下降。结果表明,增强UV-B对微粒体膜的伤害可能是一方面导致正常酶合成与分解之间的平衡失调,另一方面导致了膜脂过氧化作用。 相似文献
8.
9.
Russell DA Spatola LA Dian T Paradkar VM Dufield DR Carroll JA Schlittler MR 《Biotechnology and bioengineering》2005,89(7):775-782
Human growth hormone (hGH) is not only a valuable recombinant therapeutic protein for hormone deficiency indications, but is also an extensively characterized molecule both from recombinant bacterial systems and as circulating in humans. We describe the characterization of hGH produced in three different plant systems: tobacco cell culture, soy seed, and maize seed. The data indicate highest production in the maize seed system, with continued productivity over multiple generations, and when bred to a new host genotype for improved productivity. Purification indicated significant material of the correct structure from both plant cell culture and maize seed, with maize seed also showing correct activity relative to that produced by Escherichia coli. However, all systems showed some proteolyzed hGH, with data from gel electrophoresis, mass spectrometry, and peptide mapping localizing to a region of the protein also prone to cleavage in some other systems. Together, the data indicate the dependence of recombinant protein accumulation on posttranslational processes in different host systems. 相似文献
10.