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991.
992.
993.
MR imaging of Creutzfeldt-Jakob disease 总被引:13,自引:0,他引:13
994.
995.
Cholangiocarcinoma: delayed CT contrast enhancement patterns 总被引:17,自引:0,他引:17
996.
997.
To investigate the use of UvrB-binding to detect DNA damage, mobility shift
gel electrophoresis was used to detect binding of UvrB protein to a 136 bp
DNA fragment that was randomly adducted with aflatoxin B1 8,9- epoxide and
end-labelled with 32P. After polyacrylamide gel electrophoresis, the
shifted band that contained DNA bound by UvrB was quantified as a
percentage of total radioactive substrate DNA. This method was applied to
analyse plasmid DNA that was adducted with various DNA modifying agents in
vitro. These adducts competed for UvrB- binding to the labelled substrate.
By competing for UvrB-binding with 10 ng of plasmid DNA that was adducted
with known levels of aflatoxin B1, 2-amino-3-methylimidazo[4,5-f]quinoline,
or benzo[a]pyrene diol epoxide, UvrB competition could be quantified for
DNA adducted with between one adduct in 10(2) and one adduct in 10(5)
normal nucleotides. However, plasmid DNA exposed to N-methyl-N-nitrosourea
or methylene blue + visible light, did not compete for UvrB-binding, even
though the presence of UvrABC sensitive sites were confirmed on this DNA by
a UvrABC incision assay. Mono-adducted 96-bp DNA substrates, which
contained an internal 32P-label and either a single apurinic site,
aflatoxin B1-guanine adduct, O6-methylguanine, 8-oxo-deoxyguanosine or
non-adducted guanine, were also used as substrates for UvrA- and UvrB-
binding to examine the stability of UvrB-DNA complexes with specific
adducts. Under similar conditions used for the competition assay,
significant UvrB-binding was seen only for the aflatoxin adducted
substrate. These results suggest that stability of UvrB-binding varies
greatly between bulky and non-bulky adducts. It was also found that rat
liver DNA from untreated rats inhibited UvrB-binding to the substrate DNA
in the competition assay, to a degree that was equivalent to competition
with plasmid adducted at one adduct in 10(3) normal nucleotides.
相似文献
998.
999.
An average, variable precision error of up to 6% related to source age was observed for dual-photon absorptiometry of the spine in a longitudinal study of bone mineral content involving 393 women. Application of a software correction for source decay compensated for only a portion of this error. The authors conclude that measurement of bone-loss rates using serial dual-photon bone mineral measurements must be interpreted with caution. 相似文献
1000.
BACKGROUND: Pancreatic extracts are essential in the treatment of the majority of cystic fibrosis patients. The clinical response to different preparations is often unpredictable and at present there is no sure method of determining the best preparation for a particular patient. METHODS: Creon, Nutrizym GR, Pancrease and the high-lipase versions, Creon 25,000, Nutrizym 22 and Pancrease HL, were investigated for lipase content and resistance to simulated gastric conditions. The rates of lipase release in response to pH change, bile salts and duodenal solids were investigated. The stability of lipase and its binding to duodenal solids were also investigated. RESULTS: Declared values for lipase content were exceeded in all preparations. All preparations were acid resistant. The release of lipase in response to pH change showed notable differences in release rates. After 20 min at pH 5.5, Creon released three times the amount of lipase compared with Pancrease, the other preparations coming within the range. Above pH 5.75, the release rates were comparable amongst the preparations. Bile salts influenced release variably whilst release in a solid-rich duodenal fluid was much slower than in buffers. The released lipase was susceptible to proteolysis and pH-dependent binding to duodenal solids; these effects may compromise lipolysis. CONCLUSIONS: These results show some factors contributing to variable clinical responses to pancreatic supplements. Improvements may result if a patient is assessed on different preparations. 相似文献