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911.
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In the course of studies on the oxygenation of steroids by purified P-450 cytochromes, particularly rabbit liver microsomal cytochrome P-450 form 3b, a rapid and reliable radiometric assay has been devised for progesterone 16 alpha-hydroxylation. In view of the lack of a commercially available, suitably tritiated substrate, [1,2,6,7,16,17-3H]progesterone was treated with alkali to remove the label from potential hydroxylation sites other than the 16 alpha position. The resulting [1,7,16-3H]progesterone was added to a reconstituted enzyme system containing cytochrome P-450 form 3b, NADPH-cytochrome P-450 reductase, and NADPH, and the rate of 16 alpha-hydroxylation was measured by the formation of 3H2O. This reaction was shown to be linear with respect to time and to the cytochrome P-450 concentration. An apparent tritium isotope effect of 2.1 was observed by comparison of the rates of formation of tritium oxide and 16 alpha-hydroxyprogesterone, and the magnitude of the isotope effect was confirmed by an isotope competition assay in which a mixture of [1,7,16-3H]progesterone and [4-14C]progesterone was employed. 相似文献
915.
A C Srivastava A J Pinching M W Adler R Robertson R Higgs 《BMJ (Clinical research ed.)》1987,294(6570):495-496
Dr A C Srivastava has written to us to describe a case that raises the suggestion that people infected with the human immuno-deficiency virus (HIV) should carry identity cards. We asked two physicians, a general practitioner working with patients with the acquired immune deficiency syndrome (AIDS), and a general practitioner with a special interest in medical ethics to respond to the broad issues raised by Dr Srivastava''s letter. 相似文献
916.
Maria João Feio Trefor B. Reynoldson Verónica Ferreira Manuel Augusto S. Graça 《Hydrobiologia》2007,579(1):55-68
We sampled macroinvertebrates at 75 locations in the Mondego river catchment, Central Portugal, and developed a predictive
model for water quality assessment of this basin, based on the Reference Condition Approach. Sampling was done from June to
September 2001. Fifty-five sites were identified as “Reference sites” and 20 sites were used as “Test sites” to test the model.
At each site we also measured 40 habitat variables to characterize water physics and chemistry, habitat type, land use, stream
hydrology and geographic location. Macroinvertebrates were generally identified to species or genus level; a total of 207
taxa were found. By Unweighted Pair Group Method with Arithmetic mean (UPGMA) clustering and analysis of species contribution
to similarities percentage (SIMPER), two groups of reference sites were established. Using Discriminant Analysis (stepwise
forward), four variables correctly predicted 78% of the reference sites to the appropriate group: stream order, pool quality,
substrate quality and current velocity. Test sites’ environmental quality was established from their relative distance to
reference sites, in MDS ordination space, using a series of bands (BEAST methodology). The model performed well at upstream
sites, but at downstream sites it was compromised by the lack of reference sites. As with the English RIVPACS predictive model,
the Mondego model should be continually improved with the addition of new reference sites. The adaptation of the Mondego model
methodology to the Water Framework Directive is possible and would consist mainly of the integration of the WFD typology and
increasing the number of ellipses that define quality bands.
Handling editor: K. Martens 相似文献
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A spectroscopic method employing pulsed dye laser instrumentation is described for the determination of the 1H2O/2H2O composition of aqueous solutions by the measurement of reciprocal excited state lifetimes of EuEDTA-. The reciprocal lifetimes, gamma-1, of the 1H2O/2H2O mixtures increase linearly with the mole fraction of 1H2O. For EuEDTA- the relationship between gamma-1 and the mole fraction, chi H, of 1H2O in 1H2O/2H2O mixtures is expressed by the equation chi H = 0.37 gamma-1-0.152, with a sensitivity in chi H of +/- 0.02. The reciprocal lifetimes are independent of pH in the range 5.1 to 10.5, changes in ionic strength, and the type of buffer used in EuEDTA- containing solutions. 相似文献