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61.
Human bone marrow contains a population of haemopoietic progenitor cells that can be distinguished by their ability to adhere to preformed stromal layers (cultured in the presence of methylprednisolone [MP+] and form blast cell colonies. The stromal layers function in the colony assay after they have been heavily irradiated but not after they have been passaged. The binding of the progenitor cells to the stromal cells is complete after 2 hours of coincubation, and stromal layers of 9.6 cm2 can provide adhesion sites for at least 2,000 blast colony-forming cells. The blast colony-forming cells were shown by micromanipulation to self-renew as well as to give rise to multipotential and lineage-committed colony-forming progenitor cells. 相似文献
62.
Condensed and dispersed chromatin fractions were isolated from human placental nuclei. The DNA of each fraction was purified and characterised by isopycnic centrifugation, thermal fractionation on hydroxylapatite (HAP) and sequence complexity studies. The DNAs had identical buoyant densities in neutral CsCl (1.698 g/cm3) and similar melting profiles on HAP. Analytical ultracentrifugation in Ag+-Cs2SO4, however, showed that satellite DNAs were present in the condensed fraction DNA (DNAC) but were not visible in the dispersed fraction DNA (DNAD). In addition, DNAC was found to be enriched in highly reiterated sequences (20% reassociated by C0t 10?3) which can be correlated with the presence of satellite DNAs, whereas DNAD contained only 3% of these fast reassociating sequences. In contrast DNAD contained 30% intermediate sequences (reassociating between C0t 10?3 and C0t 100) which represent only 10% of DNAC. The reassociated highly repeated sequences of DNAC showed the presence of two components in both CsCl density gradients and HAP thermal elution studies. This suggests that either there are sequence relationships resulting in partial mismatching between the different highly repeated DNA sequences in this fraction, or that highly repeated sequences are associated with less repetitious DNA. The results are discussed in terms of possible differences in genetic activity between the chromatin fractions. 相似文献
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Two computer models for the binding of estradiol to estrogen receptors were constructed, based solely upon the thermodynamic constraints of the most likely equilibria involved and known equilibrium constants. Previous data had suggested that the positive cooperativity of the system was dependent upon a monomer-dimer equilibrium (Notides et al., Proc. natn. Acad. Sci., U.S.A. 78 (1981) 4926-4930). Using computer modeling, we confirmed that the thermodynamic constraints of a monomer-dimer equilibrium system result in convex Scatchard plots in agreement with experimental data, including the progression to linearity at low receptor concentrations. This technique yielded estimates of the equilibrium constant for dimerization (approx. 10(10) to 10(14) M-1). The dose-response characteristics of the monomer-dimer equilibrium system revealed steep dose-response curves that were sensitive to the receptor concentration. In contrast, the dose-response curves that did not undergo a monomer-dimer equilibrium system and had a single step equilibrium process were more gradual. 相似文献
67.
N Rakieten B S Gordon A Beaty R W Bates P S Schein F G Standaert 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1976,151(3):632-635
Hypoglycemic rats bearing insulin-secreting islet-cell adenomas produced by the combined action of streptozotocin and nicotinamide were treated with streptozotocin. Antitumor response was demonstrated by elevation of blood glucose, reduction in plasma and tumor IRI, and histopathologic changes in the beta-cell neoplasm. The rodent tumor model may serve as a predictive system for selection and investigation of mechanisms of action of future antitumor agents to be used in the treatment of malignant insulinoma in man. 相似文献
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