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排序方式: 共有425条查询结果,搜索用时 15 毫秒
1.
High resolution nuclear magnetic resonance study of base pairing in four purified transfer RNA molecules 总被引:3,自引:0,他引:3
The high resolution nuclear magnetic resonance spectra of hydrogen bonded protons in four purified tRNA molecules are reported. From the temperature and concentration dependence it is shown that these resonances arise from intramolecular hydrogen bonds. 相似文献
2.
31P nuclear magnetic resonance (NMR) saturation-transfer (ST) techniques have been used to measure steady-state flows through phosphate-adenosine 5'-triphosphate (ATP) exchange reactions in glucose-grown derepressed yeast. Our results have revealed that the reactions catalyzed by glyceraldehyde-3-phosphate dehydrogenase/phosphoglycerate kinase (GAPDH/PGK) and by the mitochondrial ATPase contribute to the observed ST. Contributions from these reactions were evaluated by performing ST studies under various metabolic conditions in the presence and absence of either iodoacetate, a specific inhibitor of GAPDH, or the respiratory chain inhibitor antimycin A. Intracellular phosphate (Pi) longitudinal relaxation times were determined by performing inversion recovery experiments during steady-state ATP gamma saturation and were used in combination with ST data to determine Pi consumption rates. 13C NMR and O2 electrode measurements were also conducted to monitor changes in rates of glucose consumption and O2 consumption, respectively, under the various metabolic conditions examined. Our results suggest that GAPDH/PGK-catalyzed Pi-ATP exchange is responsible for antimycin-resistant saturation transfer observed in anaerobic and aerobic glucose-fed yeast. Kinetics through GAPDH/PGK were found to depend on metabolic conditions. The coupled system appears to operate in a unidirectional manner during anaerobic glucose metabolism and bidirectionally when the cells are respiring on exogenously supplied ethanol. Additionally, mitochondrial ATPase activity appears to be responsible for the transfer observed in iodoacetate-treated aerobic cells supplied with either glucose or ethanol, with synthesis of ATP occurring unidirectionally. 相似文献
3.
Measurement of intracellular sodium concentration and sodium transport in Escherichia coli by 23Na nuclear magnetic resonance 总被引:6,自引:0,他引:6
Escherichia coli is known to actively extrude sodium ions, but little is known concerning the concentration gradient it can develop. We report here simultaneous measurements, by 23Na NMR, of intracellular and extracellular Na+ concentrations of E. coli cells before and after energization. 23Na spectra in the presence of a paramagnetic shift reagent (dysprosium tripolyphosphate) consisted of two resonances, an unshifted one corresponding to intracellular Na+ and a shifted one corresponding to Na+ in the extracellular medium, including the periplasm. Extracellular Na+ was found to be completely visible despite the presence of a broad component in its resonance; intracellular Na+ was only 45% visible. Measurements of Na+ were made under aerobic and glycolytic conditions. Na+ extrusion and maintenance of a stable low intracellular Na+ concentration were found to correlate with the development and maintenance of proton motive force, a result that is consistent with proton-driven Na+/H+ exchange as a means of Na+ transport. In both respiring and glycolyzing cells, at an extracellular Na+ concentration of 100 mM, the intracellular Na+ concentration observed (4 mM) corresponded to an inwardly directed Na+ gradient with a concentration ratio of about 25. The kinetics of Na+ transport suggest that rapid extrusion of Na+ against its electrochemical gradient may be regulated by proton motive force or intracellular pH. 相似文献
4.
Alex. G. Shulman 《The Western journal of medicine》1974,120(4):278-281
In the past century diverticular disease of the colon has changed from being almost unknown to becoming the most common disease of the colon. Studies in Britain indicated that the pathological basis of the disease is a thickening of the colonic musculature, with diverticulosis and diverticulitis developing because of increased intracolonic pressures generated by the thickened colon wall. This pressure can be sharply reduced by increased colonic bulk. Geographical and anthropological data reveal that diverticular disease results from Western civilization''s food habits, specifically the reduced fiber content in food. There is evidence that increasing the dietary intake of fiber by the addition of bran can prevent formation of diverticula and relieve the symptoms of established disease. Large scale studies are recommended both as treatment and to further test the validity of this concept. 相似文献
5.
Fetal cells in maternal blood: recovery by charge flow separation 总被引:11,自引:0,他引:11
S. S. Wachtel David Sammons Michael Manley Gwendolyn Wachtel Garland Twitty Joseph Utermohlen Owen P. Phillips Lee P. Shulman Douglas J. Taron U. R. Müller Peter Koeppen Teresa M. Ruffalo Karen Addis Richard Porreco Joyce Murata-Collins Natalie B. Parker Loris McGavran 《Human genetics》1996,98(2):162-166
Fetal blood cells can be recovered from the maternal circulation by charge flow separation (CFS), a method that obviates the
risks associated with amniocentesis and chorionic villus sampling. By CFS, we processed blood samples from 13 women carrying
male fetuses, 2 carrying fetuses with trisomy 21, and 1 who had delivered a stillborn infant with trisomy 18. On average more
than 2000 fetal nucleated red blood cells were recovered per 20-ml sample of maternal blood. Recovery of fetal cells was confirmed
by fluorescence in situ hybridization with probes for chromosomes Y, 18 and 21. After culturing of CFS-processed cells, amplification
by the polymerase chain reaction revealed Y-chromosomal DNA in clones from four of six women bearing male fetuses, but not
in clones from three women bearing female fetuses.
Received: 8 January 1996 / Revised: 22 March 1996 相似文献
6.
Differential tyrosine phosphorylation of the IFNAR chain of the type I interferon receptor and of an associated surface protein in response to IFN-alpha and IFN-beta. 总被引:11,自引:3,他引:8 下载免费PDF全文
C Abramovich L M Shulman E Ratovitski S Harroch M Tovey P Eid M Revel 《The EMBO journal》1994,13(24):5871-5877
7.
A procedure which combines thin-layer chromatography with position-sensing proportional counting has been developed for analyzing the metabolism of carcinogenic polycyclic aromatic hydrocarbons. The profiles of the metabolites of [3H]benzo(a)pyrene and 7,12-[12-14C]dimethylbenz(a)anthracene produced in cell culture were comparable when obtained by this procedure and by standard methods. However, position-sensing proportional counting allows simultaneous counting of all components of a sample within 10–20 min, and thereby permits the analysis of many hydrocarbon samples in a short time. In addition, the procedure eliminates the necessity of cutting or scraping carcinogen-containing thin-layer chromatograms. 相似文献
8.
9.
Phosphorus-31 nuclear magnetic resonance studies of wild-type and glycolytic pathway mutants of Saccharomyces cerevisiae. 总被引:19,自引:0,他引:19
G Navon R G Shulman T Yamane T R Eccleshall K B Lam J J Baronofsky J Marmur 《Biochemistry》1979,18(21):4487-4499
High-resolution phosphorus-31 nuclear magnetic resonance (31P NMR) spectra of wild-type and mutant strains of Saccharomyces cerevisiae were observed at a frequency of 145.7 MHz. Levels of various phosphorus metabolites were investigated upon addition of glucose under both aerobic and anaerobic conditions. Three mutant strains were isolated and their biochemical defects characterized: pfk lacked phosphofructokinase activity; pgi lacked phosphoglucose isomerase activity; and cif had no glucose catabolite repression of the fructose bisphosphatase activity. Each mutant strain was found to accumulate characteristic sugar phosphates when glucose was added to the cell suspension. In the case of the phosphofructokinase deficient mutant, the appearance of a pentose shunt metabolite was observed. 31P NMR peak assignments were made by a pH titration of the acid extract of the cells. Separate signals for terminal, penultimate, and central phosphorus atoms in intracellular polyphosphates allowed the estimation of their average molecular weight. Signals for glycero(3)phosphochline, glycero(3)phosphoserine, and glycero(3) phosphoethanolamine as well as three types of nucleotide diphosphate sugars could be observed. The intracellular pH in resting and anaerobic cells was in the range 6.5--6.8 and the level of adenosine 5'-triphosphate (ATP) low. Upon introduction of oxygen, the ATP level increased considerably and the intracellular pH reached a value of pH 7.2--7.3, irrespective of the external medium pH, indicating active proton transport in these cells. A new peak representing the inorganic phosphate of one of the cellular organelles, whose pH differed from the cytoplasmic pH, could be detected under appropriate conditions. 相似文献
10.