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71.
LS Chernin MK Winson JM Thompson S Haran BW Bycroft I Chet P Williams GS Stewart 《Canadian Metallurgical Quarterly》1998,180(17):4435-4441
Quorum sensing control mediated by N-acyl homoserine lactone (AHL) signaling molecules has been established as a key feature of the regulation of exoenzyme production in many gram-negative bacteria. In Chromobacterium violaceum ATCC 31532 a number of phenotypic characteristics, including production of the purple pigment violacein, hydrogen cyanide, antibiotics, and exoproteases are known to be regulated by the endogenous AHL N-hexanoyl-L-homoserine lactone (HHL). In this study we show that C. violaceum produces a set of chitinolytic enzymes whose production is regulated by HHL. The chitinolytic activity was induced in strains grown in the presence of chitin as the sole carbon source and quantitated in the secreted proteins by using p-nitrophenol analogs of disaccharide, trisaccharide, and tetrasaccharide oligomers of N-acetylglucosamine. By using 4-methylumbelliferyl analogs of the same oligomers of N-acetylglucosamine as substrates for proteins separated and renatured by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, at least six enzymes were detected: a chitobiase with high specificity to a dimeric substrate of 87 kDa, two N-acetylglucosaminidases with apparent molecular masses of 162 and 133 kDa, two endochitinases of 108 and 67 kDa, and a chitobiosidase of 56 kDa. In addition, two unidentified bands of >205 kDa were found where a tetrameric chitin derivative was used as a substrate. A pleiotropic mini-Tn5 mutant of C. violaceum (CV026) that is defective in HHL production and other quorum-sensing-regulated factors was also found to be completely deficient in chitinolytic activity. Growth of this mutant on minimal medium with chitin supplemented with culture supernatant from the C. violaceum wild-type strain or 10 microM synthetic HHL restored chitinase production to the level shown by the parental strain. These results constitute the most complete evidence so far for regulation of chitinolytic activity by AHL signaling in a gram-negative bacterium. 相似文献
72.
GS Ogg X Jin S Bonhoeffer PR Dunbar MA Nowak S Monard JP Segal Y Cao SL Rowland-Jones V Cerundolo A Hurley M Markowitz DD Ho DF Nixon AJ McMichael 《Canadian Metallurgical Quarterly》1998,279(5359):2103-2106
Although cytotoxic T lymphocytes (CTLs) are thought to be involved in the control of human immunodeficiency virus-type 1 (HIV-1) infection, it has not been possible to demonstrate a direct relation between CTL activity and plasma RNA viral load. Human leukocyte antigen-peptide tetrameric complexes offer a specific means to directly quantitate circulating CTLs ex vivo. With the use of the tetrameric complexes, a significant inverse correlation was observed between HIV-specific CTL frequency and plasma RNA viral load. In contrast, no significant association was detected between the clearance rate of productively infected cells and frequency of HIV-specific CTLs. These data are consistent with a significant role for HIV-specific CTLs in the control of HIV infection and suggest a considerable cytopathic effect of the virus in vivo. 相似文献
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Higher levels of thymidylate synthase gene expression are observed in pulmonary as compared with hepatic metastases of colorectal adenocarcinoma 总被引:1,自引:0,他引:1
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The aim of the present investigation was to determine spin lock (SL) relaxation parameters for the normal brain tissues and thus, to provide basis for optimizing the imaging contrast at 0.1 T. 68 healthy volunteers were included. On-resonance spin lock relaxation time (T1rho) and off-resonance spin lock relaxation parameters (T1rho(off), Me/Mo), MT parameters (T1sat, Ms/Mo), and T1, T2 were determined for the cortical gray matter, and for the frontal and parietal white matters. The T1rho for the frontal and parietal white matters ranged from 110 to 133 ms and from 122 to 155 ms with locking field strengths from 50 microT to 250 microT, respectively. Accordingly, the values for the gray matter ranged from 127 to 155 ms. With a locking field strength of 50 microT, T1rho(off) for the frontal and parietal white matters were from 114 to 217 ms and from 126 to 219 ms, and for the gray matter from 136 to 267 ms with the angle between the effective magnetic field (B(eff)) and the z-axis (theta) ranging from 60 degrees to 15 degrees, respectively. The T1rho of the white and gray matters increased significantly with increasing locking field amplitude (p < 0.001). The T1rho(off) decreased significantly with increasing theta (p < 0.001). T1rho and T1rho(off) with theta > or = 30 degrees were statistically significantly shorter in the frontal than in the parietal white matters (p < 0.05). The duration, amplitude and theta of the locking pulse provide additional parameters to optimize contrast in brain SL imaging. 相似文献
77.
MK Hong SW Park CW Lee DH Kang JK Song JJ Kim SJ Park MK Hong GS Mintz MB Leon 《Canadian Metallurgical Quarterly》1998,82(5):670-3, A8
We evaluated the role of intravascular ultrasound (IVUS) in 16 patients with unprotected left main coronary artery (LMCA) stenting compared with 80 patients with other (non-LMCA) native coronary artery stenting and found that (1) additional high-pressure or larger size balloon dilations were more frequently performed in LMCA stenting than in non-LMCA stenting (p <0.05) and (2) after IVUS-guided stent implantation, minimum lumen area was > or = 9 mm2 in 88% of patients who underwent LMCA stenting and in 19% of those who underwent non-LMCA stenting (p <0.001). IVUS guidance may be a more important adjunctive imaging modality in the stenting of unprotected LMCA stenoses than in stenting of non-LMCA stenoses. 相似文献
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GS Wood 《Canadian Metallurgical Quarterly》1998,29(1-2):93-101
To observe the expression of p16, pRb, cdk4 and cyclinD1 in non-small cell lung cancers, 104 cases of resected lung cancers were collected, which included squamous cell carcinomas, adenocarcinomas and large cell carcinomas. Immunohistochemistry assay was carried out. The results showed that 67% of squamous cell carcinomas and 46% of adenocarcinomas expressed p16, 64% of squamous cell carcinomas and 85% of adenocarcinomas expressed pRb and 66% of cancers expressed p16 or pRb. About 70% of the tumors expressed cyclinD1. More than 90% of the tumors expressed cdk4 and there was an increased trend with decreasing differentiation of both squamous cell carcinomas and adenocarcinomas. Sixty-seven percent of the highly differentiated and 100% of the poorly differentiated squamous cell carcinomas expressed cdk4. The aberrant p16 and pRb gene product expression played a significant role in the development and histological subtype of lung cancers by conditioning the biological behavior of NSCLC. cdk4 was an important factor in histological differentiation. 相似文献