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排序方式: 共有124条查询结果,搜索用时 62 毫秒
121.
Raphaël Delpe Daniel Maume Bruno Le Bizec Herv Pouliquen 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2000,748(2)
A very specific high-performance liquid chromatography–mass spectrometric method for the determination of natural tetracyclines was developed in order to characterise the degradation products of oxytetracycline in sediments. First, extraction used a clean up step with a Bond Elut Certify® LRC cartridge. A 3 μm Spherisorb® ODS1 column was then used with a methanol, acetonitrile and oxalic acid mobile phase gradient. Chromatographic resolution in these conditions was 3.31 between oxytetracycline and tetracycline. Two liquid chromatography–mass spectrometry methodologies based on a particle beam and a frit fast atom bombardment interface were developed. In the first approach, ionisation was performed in the negative chemical mode using methane as reacting gas. In the other case, glycerol–thioglycerol mixture was used as matrix to ensure good sensitivity. MS–MS experiment was performed to determinate oxytetracycline fragmentation pattern in the perspective of degradation product study. 相似文献
122.
Apoptosis is frequently regulated by different protein kinases including protein kinase C family enzymes. Both inhibitory and stimulatory effects were demonstrated for several of the different PKC isoforms. Here we show that the novel PKC isoform, PKCη, confers protection against apoptosis induced by the DNA damaging agents, UVC irradiation and the anti-cancer drug — Camptothecin, of the breast epithelial adenocarcinoma MCF-7 cells. The induced expression of PKCη in MCF-7 cells, under the control of the tetracycline-responsive promoter, resulted in increased cell survival and inhibition of cleavage of the apoptotic marker PARP-1. Activation of caspase-7 and 9 and the release of cytochrome c were also inhibited by the inducible expression of PKCη. Furthermore, JNK activity, required for apoptosis in MCF-7, as indicated by the inhibition of both caspase-7 cleavage and cytochrome c release from the mitochondria in the presence of the JNK inhibitor SP600125, was also suppressed by PKCη expression. Hence, in contrast to most PKC isoforms enhancing JNK activation, our studies show that PKCη is an anti-apoptotic protein, acting as a negative regulator of JNK activity. Thus, PKCη could represent a target for intervention aimed to reduce resistance to anti-cancer treatments. 相似文献
123.
Reiko Sakaguchi Hitoshi Amano Kazuo Shishido 《Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression》1988,950(3)
The nucleotide sequence (1579 bp) of tetracycline-resistance determinant and flanking regions of the cloned 5.1 kb DNA fragment from Bacillus subtilis GSY908 chromosome (Sakaguchi, R. and Shishido, K. (1988) Biochim. Biophys. Acta 949, 49–57) were determined and compared with those of the B. subtilis tetracycline-resistance plasmid pNS1981. The tetracycline-resistance structural (tet) genes of the B. subtilis GSY908 chromosome (tet BS908) and pNS1981 (tet pNS1981) were found to be highly homologous (80% identical). Both tet genes were composed of 1374 bp and 458 amino-acid residues initiating from a GTG codon preceded by a ribosome-binding site (RBS-2). Upstream from tet BS908 there exists a short open reading frame (20 amino acids) initiating from a ATG codon preceded by its own RBS (RBS-1). This leader sequence was also highly homologous to that of tet pNS1981 except for a deletion of one bp between the RBS-1 and the ATG codon. 相似文献
124.
Souichi Makino Chihiro Sasakawa Hirofumi Dambara Masanosuke Yoshikawa 《Molecular & general genetics : MGG》1986,204(1):115-119
Summary Two regions tentatively called unsA and unsR were identified on pSC101. One, unsA, corresponds to less than 650 bp of the N-terminal in the tetracycline resistance structural gene and seems to inhibit stable maintenance of pSC101. The other, unsR, is defined within the 1 kb XhoI-EcoRI region located upstream of the tetracycline resistance structural gene and is a regulatory gene clearly distinct from tetR (Unger et al. 1984); it serves as a suppressor of the unsA function. 相似文献