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81.
Harold C. Box Kenneth T. Lilga John French James L. Alderfer 《Chemico-biological interactions》1984,52(1):93-102
The effect of the carcinogen acetylaminofluorene (AAF) on nucleic acid structure was examined using 13C- and 31P-NMR spectroscopies. Conformational effects were compared in two AAF-modified dinucleoside monophosphates (ApG and GpA) and two AAF-modified deoxydinucleotides (dpApG and dpGpA). Changes in adenine 13C chemical shifts on formation of the AAF-adduct and as a function of temperature provided evidence of base stacking. Differences in fluorene 13C chemical shifts between the AAF-modified dimer and AAF-modified monomer provided evidence of fluorene stacking. The effect of forming the adduct on the phosphate backbone was examined using 31P-NMR. A correlation was demonstrated between the degree of adenine-fluorene stacking on one hand and the change in conformation of the backbone conformation on the other. 相似文献
82.
Sprague-Dawley albino rats or Long-Evans pigmented rats were exposed during the dark phase of the daily light:dark cycle to various intensities of a sunlight-stimulating white fluorescent light (0.022, 0.044, 0.110, 0.220, 0.440 or 2.200 μW/cm2) for 30 min; pineal glands and trunk blood samples were then collected and assayed for melatonin by radioimmunoassay. Albino rats exposed to irradiances of 0.110 μW/cm2 or less had pineal melatonin levels that were not significantly different from those of unexposed animals; higher irradiances significantly (P < 0.001) reduced melatonin levels. In contrast, as little as 0.022 μW/cm2 significantly (P < 0.02) reduced pineal and serum melatonin levels in the pigmented rats. These results suggest that something other than the simple presence or absence of eye pigmentation is the critical factor in determining the sensitivity of the rat's pineal to retinal-mediated photic suppression of melatonin synthesis. 相似文献
83.
Abnormal high density lipoproteins from patients with liver disease regulate cholesterol metabolism in cultured human skin fibroblasts 总被引:2,自引:0,他引:2
J S Owen H Goodall P Mistry D S Harry R C Day N McIntyre 《Journal of lipid research》1984,25(9):919-931
Apolipoprotein B (apoB) of plasma low density lipoproteins (LDL) binds to high affinity receptors on many cell types. A minor subclass of high density lipoproteins (HDL), termed HDL1, which contains apoE but lacks apoB, binds to the same receptor. Bound lipoproteins are engulfed, degraded, and regulate intracellular cholesterol metabolism and receptor activity. The HDL of many patients with liver disease is rich in apoE. We tested the hypothesis that such patient HDL would reduce LDL binding and would themselves regulate cellular cholesterol metabolism. Normal HDL had little effect on binding, uptake, and degradation of 125I-labeled LDL by cultured human skin fibroblasts. Patient HDL (d 1.063-1.21 g/ml) inhibited these processes, and in 15 of the 25 samples studied there was more than 50% inhibition at 125I-labeled LDL and HDL protein concentrations of 10 micrograms/ml and 25 micrograms/ml, respectively. There was a significant negative correlation between the percentage of 125I-labeled LDL bound and the apoE content of the competing HDL (r = -0.54, P less than 0.01). Patient 125I-labeled HDL was also taken up and degraded by the fibroblasts, apparently through the LDL-receptor pathway, stimulated cellular cholesterol esterification, increased cell cholesteryl ester content, and suppressed cholesterol synthesis and receptor activity. We conclude that LDL catabolism by the receptor-mediated pathway may be impaired in liver disease and that patient HDL may deliver cholesterol to cells. 相似文献
84.
85.
Cor Dijkema Robert Pels Rijcken Harry C.M. Kester Jaap Visser 《FEMS microbiology letters》1986,33(1):125-131
Abstract The composition of the polyol pools in Aspergillus nidulans mycelium during active growth on sucrose depends strongly on pH. At pH 2.5, only mannitol is present. A comparison between nitrate- and ammonium-grown cultures shows stimulation of the arabitol content with nitrate a former nitrogen source. When starved mycelium is incubated either with natural-abundance or 13 C-enriched glucose, label appears rapidly in mannitol and arabitol, regardless of the nitrogen source or the pH used. 相似文献
86.
87.
In an attempt to probe the topography of 5 S, 16 S and 23 S RNAs in a functionally engaged ribosome, polysomes were probed using the structure-sensitive, guanine-specifie reagent kethoxal. Reactivities of guanine residues at 38 specific ribosomal RNA sites in polysomes were compared with their corresponding reactivities in vacant 70 S ribosomes. No polysome-specific protection was seen for 5 S RNA. In 16 S RNA, positions 530, 693 or 1079, 966, 1338 and 1517 showed protection in polysomes; all of these sites have highly conserved primary and secondary structures, and include several methylated nucleotides. In 23 S RNA, polysome protection is seen at positions 277, 1071, 1475 or 2112, 2116 and 2751. We attribute polysome-specific protection either to direct contact of transfer RNA and/or messenger RNA with the protected sites or to tRNA and/or mRNA-induced changes in ribosome conformation involving the protected sites. 相似文献
88.
89.
Calcium-Dependent 4-aminopyridine stimulation of protein phosphorylation in squid optic lobe synaptosomes 总被引:1,自引:0,他引:1
Harish C. Pant Paul E. Gallant Rochelle Cohen Joseph T. Neary Harold Gainer 《Cellular and molecular neurobiology》1983,3(3):223-238
When intact synaptosomes were incubated with [gamma-32P]ATP, maximal protein phosphorylation was attained 2 min after the start of incubation. Protein phosphorylation under basal conditions was dependent on external Ca2+, and the dominant peak of phosphorylation was a 50-kd protein. Incubation of intact synaptosomes in the presence of 3-6 mM 4-aminopyridine (4-AP) caused a markedly enhanced phosphorylation of high molecular weight proteins of 90, 100, 130, and 180 kd, with no increase in the 50 or 38 kd proteins. This effect of 4-AP was dependent on external calcium ions in the incubation medium. The 4-AP effect on the high molecular weight proteins was also found in synaptosomal plasma membranes isolated from the synaptosomes. Tetraethylammonium (TEA) ions did not produce this enhancement of phosphorylation. 相似文献
90.
Analysis of Staphylococcal Enterotoxin B by the Polyacrylamide Electrophoresis Technique 总被引:1,自引:1,他引:0 下载免费PDF全文
Harold L. Baier 《Applied microbiology》1971,22(2):214-219
The electrophoretic mobility of enterotoxin B was investigated through the use of the disc electrophoresis technique. Ideal patterns were developed with a 7.5% acrylamide gel system (pH 4.3). The toxin can be separated and identified from other complex proteins such as serum or suspect samples of foods by this technique. The technique can be used as an assay method for the toxin as well as to elucidate physical changes in the toxin due to temperature. The method should not be considered exclusive for enterotoxin B. 相似文献