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101.
Expression and posttranslational processing of preprodynorphin complementary DNA in the mouse anterior pituitary cell line AtT-20 总被引:2,自引:0,他引:2
A recombinant plasmid containing the rat prodynorphin cDNA was introduced into the mouse anterior pituitary corticotroph cell line AtT-20. These cells normally express and posttranslationally process proopiomelanocortin, but not prodynorphin. Stable transformants were isolated and analyzed for the expression and processing of prodynorphin. The stably transformed AtT-20 cells that expressed a 1.3-kilobase prodynorphin mRNA also expressed prodynorphin protein and processed it to dynorphin peptides. The peptides included leucine-enkephalin, beta-neoendorphin, dynorphin-A8, and dynorphin-B, as identified by gel filtration and reverse phase HPLC followed by RIA using peptide-specific antisera. These results demonstrate that AtT-20 cells efficiently and accurately process prodynorphin at both dibasic sites and monobasic cleavage sites, indicating that the AtT-20 cells contain enzymes capable of cleaving the precursor not only at dibasic residues but also at monobasic residues. The release of prodynorphin-derived peptides paralleled secretion of endogenous proopiomelanocortin-derived peptides when stimulated by CRF, a natural secretagogue for ACTH. 相似文献
102.
Treatment of rat intestinal epithelial cells (IEC-6 cells) with lanosterol 14 alpha-demethylase inhibitors, ketoconazole and miconazole, had similar effects on 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity and cholesterol biosynthesis but the drugs differed in their ability to prevent the low density lipoprotein (LDL) suppression of reductase activity. Miconazole, at concentrations that inhibited the metabolism of lanosterol and epoxylanosterol to the same degree as ketoconazole, did not prevent low density lipoprotein action on reductase activity, whereas ketoconazole totally abolished the low density lipoprotein action on reductase activity. Both drugs caused: 1) a biphasic response in reductase activity such that at low concentrations (less than 2 microM) reductase activity was inhibited and at high concentrations (greater than 5 microM) the activity returned to control or higher than control levels; 2) an inhibition of metabolism of lanosterol to cholesterol, and 24(S), 25-epoxylanosterol to 24(S), 25-epoxycholesterol. Neither drug prevented suppression of reductase activity by 25-hydroxylanosterol, 25-hydroxycholesterol, or mevalonolactone added to the medium. Each drug increased the binding, uptake, and degradation of 125I-labeled LDL and inhibited the re-esterification of free cholesterol to cholesteryl oleate and cholesteryl palmitate. The release of free cholesterol from [3H]cholesteryl linoleate LDL could not account for the differential effect of ketoconazole and miconazole on the prevention of low density lipoprotein suppression of reductase activity. The differential effect of the drugs on low density lipoprotein suppression of reductase activity was not unique to IEC-6 cells, but was also observed in several cell lines of different tissue origin such as human skin fibroblast cells (GM-43), human hepatoblastoma cells (HepG2), and Chinese hamster ovary cells (wild type, K-1; 4 alpha-methyl sterol oxidase mutant, 215). These observations suggest that the suppressive action of low density lipoprotein on reductase activity 1) does not require the de novo synthesis of cholesterol, or 24(S), 25-epoxysterols; 2) is not mediated via the same mechanism as that of mevalonolactone; and 3) does not involve cholesteryl reesterification. Ketoconazole blocks a site in the process of LDL suppression of reductase activity that is not affected by miconazole. 相似文献
103.
The features of the Laboratory Accreditation Program of the American Society of Cytology that pertain to quality assurance in cytopathology are reviewed. The areas considered include: (1) specimen procurement and cytopreparation, (2) the role of the cytotechnologist in cytoscreening, evaluation and reporting, (3) the role of the cytopathologist and (4) quality control measures. Attention to the issues raised in these areas is essential to achieving the best possible cytopathology practice in the most efficient and economical manner. 相似文献
104.
The effects of denervation and hindlimb suspension induced disuse on concentrations of ATP, phosphocreatine (PC), and fiber type profile were investigated in slow twitch soleus and fast twitch extensor digitorum longus (EDL) muscles. The results show that the soleus and EDL muscles differ in their dependency on loadbearing as a stimulus for maintaining normal energy metabolism and the biochemical and morphological characteristics of muscle fibers. As determined by R-P methodology, suspension reduced ATP and PC concentrations of the soleus to 26% and 56%, respectively, while, in EDL only, PC is reduced to 71% of control with no change in ATP. Both muscles, however, show identical losses in ATP and PC following denervation. The energy charge, an indicator of Pi availability in muscle was reduced significantly in both denervated muscles to 82% and 85% in soleus and EDL, respectively. No significant reduction of the energy charge was seen in the muscles from suspended rats. Thus, in parallel with the indirect regulation through muscle loadbearing, the nerve can effectively modulate the levels of high-energy phosphates more directly by some regulatory mechanisms independent of muscle type. Denervation and suspension disuse increased the proportion of type 2 fibers in the soleus with a concomitant decrease in type 1 fibers and a relative rise in the number of very small diameter fibers. The EDL showed only variation in fiber size. 相似文献
105.
Growth of cell suspension cultures of tomato, Lycopersicon esculentum Mill. cv VFNT-Cherry, in the presence of cadmium is inhibited by buthionine sulfoximine, an inhibitor of glutathione synthesis. Cell growth and phytochelatin synthesis are restored to cells treated with buthionine sulfoximine by the addition of glutathione to the medium. Glutathione stimulates the accumulation of phytochelatins in cadmium treated cells, indicating that availability of glutathione can limit synthesis of these peptides. Exogenous glutathione causes a disproportionate increase in the level of smaller phytochelatins, notably [γ-Glu-Cys]2-Gly. In the presence of buthionine sulfoximine and glutathione, phytochelatins that are produced upon exposure to cadmium incorporate little [35S]cysteine, indicating that these peptides are probably not synthesized by sequential addition of cysteine and glutamate to glutathione. 相似文献
106.
Changes in the cell surface of vaginal epithelial cells were studied by scanning microscopy and fluorescence spectroscopy. Microvilli which are prominent features of the vaginal epithelial cells in proestrus and diestrus are replaced by sheet-like structures in the estrus phase. Surface morphology of vaginal epithelial cells of estradiol primed rat resembles the vaginal cells from estrus phase rats whereas vaginal cells from control rats resembles the diestrus phase. Measurement of the fluidity of the membranes indicated that the vaginal epithelial cell membrane of estrus rats is more fluid compared to proestrus and diestrus. Similarly, estradiol primed immature rat vaginal epithelial cell membrane was observed to be more fluid than the corresponding control. 相似文献
107.
Magnetically controlled targeted micro-carrier systems 总被引:11,自引:0,他引:11
Magnetically controlled targeted drug delivery systems are aimed at concentrating drugs at a defined target site, with the aid of a magnetic field. This technique has been developed specifically for directing drugs away from the reticuloendothelial system (RES). Literature on this topic suggests that these delivery systems are capable of altering the distribution of chemotherapeutic agents in the body. Hence these delivery devices offer the possibility of improving the therapeutic efficacy of the associated drugs. This paper reviews the work done to date towards the development and evaluation of biodegradable and non-biodegradable magnetic targeted drug delivery systems and outlines their future prospects and limitations in cancer chemotherapy. 相似文献
108.
A cytomorphologic diagnosis of tuberculous lymphadenitis by examination of needle aspirates was made in 560 of 1,471 cases of lymphadenopathy studied over two years. Cytologic features were categorized into four groups: epithelioid clusters with or without Langhans's giant cells without necrosis (32.14%), epithelioid clusters with or without Langhans's giant cells with necrosis (50.35%), occasional epithelioid cells without characteristic necrosis/giant cells (2.85%) and necrosis without epithelioid clusters or Langhans's giant cells (14.64%). While a diagnosis of tuberculous lymphadenitis was offered with confidence in the first two groups, constituting about 82.49% cases, aspirates from the third- and fourth-group patients were subjected to Ziehl-Neelsen staining for acid-fast bacilli, which was positive in 12.5% and 75.6% of cases, respectively. 相似文献
109.
A novel approach for chemically deglycosylating O-linked glycoproteins. The deglycosylation of submaxillary and respiratory mucins. 总被引:2,自引:0,他引:2
A new approach for removing O-glycosidically linked carbohydrate side chains from glycoproteins is described. Periodate oxidation of the C3 and C4 carbons in peptide-linked N-acetylgalactosamine (GalNAc) residues generates a dialdehyde product which, under mild alkaline conditions, undergoes a beta-elimination which releases carbohydrate and leaves an intact peptide core. The pH and time dependence, and intermediates of the elimination, have been extensively followed by carbon-13 NMR spectroscopy and amino acid analysis using ovine submaxillary mucin (OSM) as the substrate. The deglycosylation of OSM is complete and provides apomucin in high yield with an amino acid composition identical to the starting material. Carboxymethylated OSM when deglycosylated by this method gives an apomucin with an apparent molecular weight of ca. 700 x 10(3). The molecular weight is the same as that calculated for the peptide core of the starting mucin, demonstrating the absence of peptide core cleavage. This contrasts with the use of trifluoromethanesulfonic acid (TFMSA), which generates apomucin products of lower molecular weights. Oligosaccharide side chains substituted at C3 of the peptide-linked GalNAc residue are resistant to the oxidation and elimination. Glycoproteins containing these more complex side chains can be deglycosylated by pretreatment with TFMSA under mild (0 degree C) conditions, which removes peripheral sugars (while leaving the peptide-linked GalNAc residue intact), followed by oxidation and beta-elimination. Studies on the deglycosylation of porcine submaxillary mucin and human tracheobronchial mucin indicate that this approach provides more efficient removal of carbohydrate and less peptide core degradation than a more vigorous (25 degrees C) treatment with TFMSA alone. 13C NMR spectroscopic studies and carbohydrate analysis of the deglycosylation intermediates of the human mucin indicate that certain sialic acid containing and N-acetylglucosamine-containing oligosaccharides have elevated resistance to TFMSA treatment at 0 degrees C. By the use of neuraminidase, repeated mild TFMSA treatments, and multiple oxidations and beta-eliminations, the human mucin can be nearly completely deglycosylated. It is expected that all mucins and most glycoproteins containing O-glycosidic linkages can be readily and nearly completely deglycosylated using this combined approach. 相似文献
110.
Evidence is presented here to show that 20-hydroxyecdysone is essential for the activation of the larval fat body for differential uptake of larval haemolymph proteins (LHPs). By using radiolabelled LHPs it is shown that the fat body cells of Corcyra cephalonica selectively incorporate LHPs during late-larval and prepupal development. Fluorographic analysis of the labelled fat body proteins from prepupal stage separated on sodium dodecyl-sulphate polyacrylamide gels suggests that the LHPs are sequestered without any degradation. Although, during the last larval instar the uptake of all the three LHPs (LHP 1, LHP 2 and LHP 3) by the fat body cells is very low, 20-hydroxyecdysone treatment of early, mid or late-last instars causes a significant increase in uptake of all the three LHPs. However, the response to hormone treatment was more pronounced in late-last instar when compared to early and mid-last instar. 相似文献