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121.
There is considerable evidence suggesting that the switch from to and chain production after birth is due, in part, to silencing of the genes by stage-specific factors which bind to their promoters and to the competition from the adult ( and ) genes for a common enhancer element located in the locus control region. As a consequence one can expect that the increased Hb F production in adults with hereditary persistence of fetal hemoglobin or -thalassemia is directed mainly by -globin genes in cis to the deletion(s) responsible for these conditions. Here we review data on heterozygotes with -, -, or -thalassemia, who also had anAT mutation, in cis or in trans, which was used as a marker of gene expression. The results show that a deletion affecting adult genes favors the expression of genes in cis, while the deletion of a single gene does not affect the expression of the gene in cis but leads to a faster switch postnatally.  相似文献   
122.
Ecdysteroids in diapause eggs of the silkworm,Bombyx mori, were analyzed using high-performance liquid chromatography (HPLC) combined with radioimmunoassay (RIA). A relatively large amount of an unidentified free ecdysteroid and its phosphoric ester (conjugated form) were detected. These two compounds were isolated by a combination of column chromatography on silicic acid, thin-layer chromatography (TLC), and HPLC using a reverse-phase (RP) column. The purified compounds were identified as 3-epi-22-deoxy-20-hydroxyecdysone (22d20E) and 3-epi-22-deoxy-20-hydroxyecdysone 2-phosphate (22d20E2P) by means of mass spectrometry and nuclear magnetic resonance spectroscopy. to our knowledge, this is the first report of 22d20E and 22d20E2P.  相似文献   
123.
The main component of the sex pheromone secretion of femaleDiprion pini L. (Hymenoptera: Diprionidae) from insects collected both in Finland and in France has been identified as athreo-3,7-dimethyl-2-tridecanol (8 ng per female) stereoisomer by GC-MS and synthesis. The secretion also contains lower and higher homologues in small amounts (1–4% of the main component). Combined gas chromatographic-electroantennographic detection showed activity in both natural and esterified extracts (acetates and propionates); the esters of the main component gave the largest responses. The acetates and propionates of the eight stereoisomers of 3,7-dimethyl-2-tridecanol were synthesized from enantiomerically highly enriched (>99% ee) building blocks. The stereochemistry of the main component was established to be (2S,3R,7R)-3,7-dimethyl-2-tridecanol by GC analysis of the natural material. It was purified by liquid chromatography prior to the GC analysis of both its pentafluorobenzoates and its isopropylcarbamates on a non-chiral polar column (ECD) and a chiral column (NPD), respectively. Field tests demonstrated that both the acetate and propionate of the main component (100 g of each applied on cotton roll dispensers) were active in attracting males, with or without the presence of several of the minor compounds. Experiments with smaller amounts of the acetate and the propionate (1 g in France and 50 g in Finland) demonstrated that the propionate was more active than the acetate, and that it also caught more males than a blend of the two compounds.  相似文献   
124.
Atmospheric carbon dioxide concentrations before 2.2 billion years ago   总被引:5,自引:0,他引:5  
Rye R  Kuo PH  Holland HD 《Nature》1995,378(6557):603-605
The composition of the Earth's early atmosphere is a subject of continuing debate. In particular, it has been suggested that elevated concentrations of atmospheric carbon dioxide would have been necessary to maintain normal surface temperatures in the face of lower solar luminosity in early Earth history. Fossil weathering profiles, known as palaeosols, have provided semi-quantitative constraints on atmospheric oxygen partial pressure (pO2) before 2.2 Gyr ago. Here we use the same well studied palaeosols to constrain atmospheric pCO2 between 2.75 and 2.2 Gyr ago. The observation that iron lost from the tops of these profiles was reprecipitated lower down as iron silicate minerals, rather than as iron carbonate, indicates that atmospheric pCO2 must have been less than 10(-1.4) atm--about 100 times today's level of 360 p.p.m., and at least five times lower than that required in one-dimensional climate models to compensate for lower solar luminosity at 2.75 Gyr. Our results suggest that either the Earth's early climate was much more sensitive to increases in pCO2 than has been thought, or that one or more greenhouse gases other than CO2 contributed significantly to the atmosphere's radiative balance during the late Archaean and early Proterozoic eons.  相似文献   
125.
The seeding of an expanse of surface waters in the equatorial Pacific Ocean with low concentrations of dissolved iron triggered a massive phytoplankton bloom which consumed large quantities of carbon dioxide and nitrate that these microscopic plants cannot fully utilize under natural conditions. These and other observations provide unequivocal support for the hypothesis that phytoplankton growth in this oceanic region is limited by iron bioavailability.  相似文献   
126.
The antiviral activities of some naturally occurring anthraquinones bianthrones, and hypericin derivatives were compared by the end-point CPE (viral cytopathic effects) method and plaque assays. Under optimal conditions of exposure to light, hypericin, 7,7-dichlorohypericin and 5,7-dichloroemodin exhibited strong inhibitory activity against HSV-1 (herpes simplex virus type 1) in both assays. Partial inactivation of the virus was shown by emodin, 7-chloroemodin and 7-chloro-1-O-methylemodin; the bianthrones and other anthraquinones were found to be inactive. Antiviral activity appeared to be, positively correlated with increasing substitution of chlorine in the anthraquinone structure. In the absence of light, only hypericin and 7,7-dichlorohypericin displayed detectable activity.  相似文献   
127.
The immunization of biungulate animals with killed foot-and-mouth disease virus (FMDV) requires periodic vaccinations due to a low vaccine immunogenicity. Therefore, FMDV antigens need to be combined with adjuvants such as aluminum hydroxide, saponin or oil emulsions. Animal handling for periodic inoculations, and the repeated doses of vaccines that have to be administered increase the commercialization costs. Moreover, the use of adjuvants may induce adverse effects.In the present work we show that it is possible to increase the life span of neutralizing antibodies in serum when a single dose of cyclophosphamide (Cy) is administered four days before vaccination with aluminum hydroxidesaponin FMDV vaccine.  相似文献   
128.
Most air pollutants do not lead to specific diseases. Depending on the pollutant, the concentration and the duration of exposure, some organs are more affected than others. The most frequent disorders are those caused by irritant gases and particulates on the mucous membranes and respiratory organs. The consequences are eye, nose and throat inflammations, diminished lung function, increased susceptability to respiratory infection and a higher incidence of chronic bronchitis. These disorders and diseases are, of course, influenced by other factors as well, such as immune deficiency, allergies, occupational exposure to pollutants, and particularly smoking. The effects of air pollutants are, therefore, multifactorially conditioned and nonspecific disorders are placed in the foreground. Evidence for an association of air pollution with adverse effects on human health is drawn from three sources: animal experiments, experimental human exposures, and epidemiologic studies of exposed human populations. The burden of atmospheric pollution must be reduced to protect human health by an adequate safety margin. In particular, the increased sensitivity of sick and aged people as well as children should be taken into account. In defining the maximum emmission levels, preventive aspects should have priority so as to keep the risk of damage to health and the harmful influences on the environment to a minimum.This article Effects of atmospheric pollution on human health by H. U. Wanner is a revised version of the same article that was first published in the Proceedings of the 1990 European Aerosol Conference; special issue of the J. Aerosol Sci., Vol. 21, Suppl. 1 (1990) 389–396.Reprinted with kind permission from Pergamon Press Ltd, Headington Hill Hall, Oxford OX3 0BW, Great Britain.  相似文献   
129.
Transgenic cultigens may become feral as we know of some non-transgenic cultigens. The article explains two basic ways how cultigens become feral: through hybridization with a closely related wild plant and through revert to the wild-type. A long list of examples of cultigens becoming feral in Central Europe is presented. The process of becoming feral is compared to the naturalization of non-native species (Exotic Species Model). Ecological long-term effects of both cultigens becoming feral and non-native species being naturalized are discussed with special regard to the predictability of such events. The ecological aspects discussed in the article are as significant for transgenic cultigens as for non-transgenic cultigens.  相似文献   
130.
The vascular effects of 2-mercaptoethanol, cysteamine, L-cysteine, glutathione (GSH), cystamine and oxidized GSH (GSSG) on the isometric tension of isolated dog coronary arterial strips were examined, and these effects were compared with the triphasic response induced by dithiothreitol (DTT); a rapid and weak contraction (phase A), an intervening slow relaxation (phase B) and a slowly-developing strong contraction (phase C) which we previously reported. The responses of the arteries induced by 2-mercaptoethanol, cysteamine and L-cysteine consisted of phases A, B and C. The order of contractile potency (ED50 of phase C) was DTTL-cysteine>2-mercaptoethanolcysteamine, while the order of relaxant potency (ED50 of phase B) was DTT>cysteamine2-mercaptoethanol. GSSG and cystamine mainly produced relaxation, which corresponded to phase B. The phase C contraction was specific to the reduced forms of thiols, except for GSH, which produced only relaxation. The participation of endothelial cells was not essential for the contracting or relaxing effects of the thiol compounds. The phase C contraction was depressed by W-7, a calmodulin antagonist, while phase A was not. Therefore calmodulin-dependent protein kinases may participate in phase C, not in phase A.  相似文献   
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