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991.
992.
Hierarchical down-modulation of hemopoietic growth factor receptors   总被引:31,自引:0,他引:31  
F Walker  N A Nicola  D Metcalf  A W Burgess 《Cell》1985,43(1):269-276
Granulocytes and macrophages can be produced in vitro when progenitor cells from mouse bone marrow are stimulated by any of four distinct colony stimulating factors, Multi-CSF (IL-3), GM-CSF, G-CSF, and M-CSF (CSF-1). At 0 degrees C the four CSFs do not cross-compete for binding to bone marrow cells, indicating that each has a specific cell surface receptor. However, at 21 degrees C or 37 degrees C, Multi-CSF inhibits binding of the other three CSFs and GM-CSF inhibits binding of G-CSF and M-CSF. Rather than competing directly for receptor binding, the binding of Multi-CSF, GM-CSF, or G-CSF to their own receptor induces the down-modulation (and thus activation) of other CSF receptors at 37 degrees C. The pattern and potency of down-modulation activity exhibited by each type of CSF parallels the pattern and potency of its biological activity. We propose a model in which the biological interactions of the four CSFs are explained by their ability to down-modulate and activate lineage-specific receptors.  相似文献   
993.
Presented a choice between conspecific males and 2 congeneric males, virgin females ofMelittobia australica andM. digitata chose conspecific males disproportionately more often, whereasM. femorata females distributed themselves evenly among the choices. Empty tubes, provided as the fourth choice in the test apparatus, were entered much less often than tubes containing live males. Females of all species chose “wrong” males about equally frequently. These observations suggest that even non-conspecific males possess some degree of attractiveness to virgin females. Chemicals in the sex pheromone of the males are presumed to be the source of the males' attractancy. The incomplete species specificity is interpreted in light of the life history of this genus, and it is suggested that specific recognition cues operate primarily after the sexes come together. Supported by a grant from Kagoshima Prefecture in Japan under the exchange program of faculty members between Kagoshima University and the University of Georgia.  相似文献   
994.
The extracellular protease, endopeptidase, and hexosaminidase produced by Staphylococcus, simulans biovar staphylolyticus were neither induced nor repressed by amino acids but required a tryptic digest of casein for their production. Catabolite repression of exoenzyme production by glucose was not affected by exogenous cyclic adenosine 3′, 5′-monophosphate but was partially relieved by di- or monobutyryl derivatives of this compound.  相似文献   
995.
996.
The extraction of a tissue collagenase associated with ovulation in the rat   总被引:2,自引:0,他引:2  
A method has been developed to assay collagenase in ovarian extracts in the presence of tissue inhibitors. Rat ovarian tissue is first extracted with Triton X-100 and then heated to 60 degrees C in 50 mM Tris buffer containing 100 mM CaCl2. This extract contains collagenase activity and putative inhibitor(s). The inhibitory activity is removed by reduction with dithiothreitol and alkylation with iodoacetamide. Collagenase is then activated with aminophenylmercuric acetate and assayed using 3H-acetylated collagen from which the telopeptides have been removed. Identification of this activity as collagenase was performed by using the metalloprotease inhibitors EDTA and o-phenanthroline and by demonstration of the typical collagen cleavage fragments on sodium dodecyl sulfate-gel electrophoresis. To investigate the changes in collagenase activity associated with ovulation, immature rats received 20 IU of pregnant mare's serum gonadotropin and 52 h later 10 IU of human chorionic gonadotropin (hCG). After hCG administration, ovaries were removed at intervals from 0 to 20 h. Collagenase activity rose from 4.9 +/- 1.4% digestion of the 3H-collagen at 0 time to a maximum of 24.7 +/- 1.5% digestion at 8 h after hCG and remained high at 12 h (time of ovulation) and up to 20 h (18.7 +/- 1.9% and 16.1 +/- 1.6% digestion, respectively). These findings support a role of collagenase in the rupture of the follicle and they suggest a further role for this enzyme in the events following ovulation.  相似文献   
997.
In this study, we examined the effects that antifreeze proteins have on the supercooling and ice-nucleating abilities of aqueous solutions. Very little information on such nucleation currently exists. Using an automated lag time apparatus and a new analysis, we show several dilution series of Type I antifreeze proteins. Our results indicate that, above a concentration of ∼8 mg/ml, ice nucleation is enhanced rather than hindered. We discuss this unexpected result and present a new hypothesis outlining three components of polar fish blood that we believe affect its solution properties in certain situations.  相似文献   
998.
On 11 May 1985 the main stand of Bradford City Football Club caught fire. Within four minutes the stand was alight from end to end. Fifty three people were burnt to death and about 250 injured; 83 required admission to hospital, and 55 of these were treated by primary excision of their burns and skin grafting. In such disasters the help of staff from other hospitals and areas is essential. Patients should be assessed to see whether they have burns that will ultimately be fatal; if they have they should not be sent to regional burns units, where they would take up beds that could be used for patients with treatable burns. All districts should ensure that their plans for accidents in which burns injuries predominate are adequate.  相似文献   
999.
1000.

Background  

Ontario provincial abattoirs have the potential to be important sources of syndromic surveillance data for emerging diseases of concern to animal health, public health and food safety. The objectives of this study were to: (1) describe provincially inspected abattoirs processing cattle in Ontario in terms of the number of abattoirs, the number of weeks abattoirs process cattle, geographical distribution, types of whole carcass condemnations reported, and the distance animals are shipped for slaughter; and (2) identify various seasonal, secular, disease and non-disease factors that might bias the results of quantitative methods, such as cluster detection methods, used for food animal syndromic surveillance.  相似文献   
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