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1.
Cristian A. Acevedo Elizabeth Y. Sanchez Juan G. Reyes Manuel E. Young 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2010,878(3-4):449-455
It is known that skin releases volatile organic compounds to the environment, and also that its emission pattern changes with aging of the skin. It could be considered, that these compounds are intermediaries in cell metabolism, since many intermediaries of metabolic pathways have a volatile potential. In this work, a simple and non-destructive method consisting of SPME sampling and GC/MS analysis was developed to identify volatile organic emanations from cell cultures. This technique, applied to skin cells culture, indicates that the cells or cell metabolism produce several skin emissions. Chemometric analysis was performed in order to explore the relationship between a volatile profile and the senescence of cell cultures. Volatile profiles were different for cell cultures in different degrees of senescence, indicating that volatile compound patterns could be used to provide information about the age of skin cells. 相似文献
2.
On the binding of tRNA to Escherichia coli RNA polymerase. Interactions between the core enzyme, DNA and tRNA 总被引:7,自引:0,他引:7
We have investigated the interplay between the binding of tRNA and DNA to core RNA polymerase. We show that the monomer core enzyme can bind stably to either DNA or tRNA, whereas the dimer core can fix both DNA and tRNA in a stable ternary complex. We have examined the kinetics of the exchange between DNA and tRNA bound to the core enzyme. DNA bound to monomer core can be rapidly displaced by tRNA without prior dissociation of the core from the DNA. Similarly tRNA bound to the core can be displaced by DNA without prior dissociation of the tRNA. We confirm the result of Hinkle and Chamberlin [J. Mol. Biol. 70, 157-185 (1972)] that, in contrast, the core enzyme must first dissociate from one DNA molecule before it can transfer to another DNA. As this dissociation is very slow we suggest that, in vivo, the tRNA can act as a 'porter' providing the core enzyme with a more kinetically favourable path to transfer from one DNA site to another. 相似文献
3.
The daily and seasonal distribution of airborne fungal particles was recorded in a high altitude tropical zone. Sampling was
carried out in the southern part of Mexico City. An Andersen air sampler was used over a period of six months. Ten minutes
sampling for each set of plates was done at fixed schedule: 07:30, 14:00 and 19:00 hours. The sampler was placed 10 m above
the ground. Daily variation was found to be associated with the season, weather and atmospheric stability. The highest value
of mold counts (3195 CFU m−3) was recorded in the evening on October, a transitional month between the rainy and the dry seasons, the lowest (45 CFU m−3) at noon during the rainy season. Mold counts were significantly correlated with temperature, having negative signs both
in the morning and at noon, and being positive in the evening. The abundance of only three genera was recorded.Cladosporium, was isolated more frequently, and its abundance at 14:00 h was of 38%;Alternaria represented 4.0%, at 14:00 h, andAspergillus 3.0% at 7:30 h. Fifteen species belonging to the latter genera were identified and most of them are considered as opportunistic
molds of clinical significance. 相似文献
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Metabolic regulation in enzyme-deficient red cells 总被引:1,自引:0,他引:1
6.
Overproduction of threonine by Saccharomyces cerevisiae mutants resistant to hydroxynorvaline.
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In this work, we isolated and characterized mutants that overproduce threonine from Saccharomyces cerevisiae. The mutants were selected for resistance to the threonine analog alpha-amino-beta-hydroxynorvalerate (hydroxynorvaline), and, of these, the ones able to excrete threonine to the medium were chosen. The mutant strains produce between 15 and 30 times more threonine than the wild type does, and, to a lesser degree, they also accumulate isoleucine. Genetic and biochemical studies have revealed that the threonine overproduction is, in all cases studied, associated with the presence in the strain of a HOM3 allele coding for a mutant aspartate kinase that is totally or partially insensitive to feedback inhibition by threonine. This enzyme seems, therefore, to be crucial in the regulation of threonine biosynthesis in S. cerevisiae. The results obtained suggest that this strategy could be efficiently applied to the isolation of threonine-overproducing strains of yeasts other than S. cerevisiae, even those used industrially. 相似文献
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Axel Kahn Hélène-Annie Buc Robert Girot Dominique Cottreau Claude Griscelli 《Human genetics》1978,40(3):293-304
Summary Two new deficient glucose-phosphate-isomerase (GPI) variants have been described in patients suffering from severe chronic hemolytic anemias. The patients' parents were consanguineous, such that the patients were true homozygotes for the mutated GPI genes. In both cases the main cause of the defect in enzyme activity was molecular instability of the mutated GPI molecules, their catalytic activity being nearly normal.GPI Paris was characterized by a slow electrophoretic migration and, above all, a drastically altered affinity for the substrates glucose-6-phosphate (decreased) and fructose-6-phosphate (increased). GPI Enfants malades exhibited a slightly reduced electrophoretic mobility, an abnormal curve of the activity in function of pH, and an abnormal ratio of maximal velocity in the backward direction (fructose-6-phosphate»glucose-6-phosphate) to that in the forward direction (glucose-6-phosphate»fructose-6-phosphate).No clear relation could be proved between the kinetic abnormalities of the mutant GPI variants on the one hand and the metabolic changes of the GPI-deficient red cells and the severity of hemolysis on the other.Finally we emphasized the possible role of the impairment of hexosemonophosphate pathway in the reduction of viability of the GPI-deficient red cells. 相似文献