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21.
Abstract. The CFU-s proliferative potential varied greatly during long-term cultivation. Most of the CFU-s in the cultures were represented by cells with low renewal capacity. Pre-CFU-s cells capable of producing multipotential colonies in methylcellulose, which contained CFU-s with a high proliferative potential, were identified in the culture. In cultivation of a mixture of cells of different karyotype their ratio changed rapidly from week to week. the findings were consistent with the hypothesis that haemopoietic stem cells are maintained in the culture by the products of a small number of clones which arise and decline in succession, and that pre-CFU-s, but not the CFU-s themselves, are clonogenic progenitors. 相似文献
22.
Comparison of small proteoglycans from skin fibroblasts and vascular smooth-muscle cells. 总被引:7,自引:3,他引:4
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Physicochemical and chemical properties of small proteoglycans containing galactosaminoglycan chains from cultured human skin fibroblasts and human smooth-muscle cells were compared to determine the extent of structural similarity. The proteoglycan secreted by smooth-muscle cells was of larger molecular size and of higher buoyant density, due to longer glycosaminoglycan chains, than the secretion product of skin fibroblasts. Additionally, both proteoglycans differed in the ratio of iduronic acid and glucuronic acid residues. On the other hand, degradation of secreted [3H]leucine-labelled proteoglycans with chondroitin ABC lyase followed by SDS/polyacrylamide-gel electrophoresis resulted in the appearance of core protein bands of identical size (Mr 48,000 and 45,000, depending on the number of asparagine-bound oligosaccharides). An Mr value of 40,000 was determined for the core protein of cells pretreated with tunicamycin. An antibody against the core protein from fibroblast secretions was cross-reactive with the core protein from smooth-muscle cells. Core protein accumulating intracellularly after treatment with carbonyl cyanide m-chlorophenylhydrazone exhibited, on reduction and alkylation, an isoelectric point of 7.8 in both cell types. Limited proteolysis by staphylococcal V8 serine proteinase or endoproteinase Lys-C led in both instances to the formation of peptides of identical size. Peptides bearing asparagine-bound oligosaccharides were free of glycosaminoglycan chains. Similar peptide patterns were obtained when 125I-labelled core proteins were digested with either trypsin or chymotrypsin. Thus small proteoglycans from fibroblasts and smooth-muscle cells can be differentiated by their glycosaminoglycan moieties but not by the nature of their core proteins. 相似文献
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26.
Flemming S. Vassbotn Arne
stman Nina Langeland Holm Holmsen Bengt Westermark Carl-Henrik Heldin Monica Nistr 《Journal of cellular physiology》1994,158(2):381-389
Human glioblastoma cells (A172) were found to concomitantly express PDGF-BB and PDGF β-receptors. The receptors were constitutively autophosphorylated in the absence of exogenous ligand, suggesting the presence of an autocrine PDGF pathway. Neutralizing PDGF antibodies as well as suramin inhibited the autonomous PDGF receptor tyrosine kinase activity and resulted in up-regulation of receptor protein. The interruption of the autocrine loop by the PDGF antibodies reversed the transformed phenotype of the glioblastoma cell, as determined by (1) diminished DNA synthesis, (2) inhibition of tumor colony growth, and (3) reversion of the transformed morphology of the tumor cells. The PDGF antibodies showed no effect on the DNA synthesis of another glioblastoma cells line (U343MGa 31L) or on Ki-ras-transformed fibroblasts. The present study demonstrates an endogenously activated PDGF pathway in a spontaneous human glioblastoma cell line. Furthermore, we provide evidence that the autocrine PDGF pathway drives the transtormed phenotype of the tumor cells, a process that can be blocked by extracellular antagonists. © 1994 Wiley-Liss, Inc. 相似文献
27.
Abstract: Magnesium and the polyamines putrescine, spermidine, and spermine inhibited the activity of glutamate dehydrogenase in permeabilized rat brain mitochondria in a concentration-dependent manner. The inhibitory effect was observed on both the reductive amination of 2-oxoglutarate and oxidative deamination of glutamate, as well as in the presence and absence of ADP and leucine, the allosteric activators of the enzyme. Kinetic studies at various concentrations of substrates showed that inhibition by magnesium and spermine was very pronounced at 2-oxoglutarate concentrations less than 0.5 m M and NADH levels less than 0.08 m M . The presence of the former compounds also accentuated the inhibitory effect of high concentrations of 2-oxoglutarate (>2.0 m M ) and NADH (>0.32 m M ). Addition of magnesium and spermine to suspensions of synaptosomes decreased the amount of ammonia produced from glutamate. It is suggested that polyamines and magnesium, normal constituents of mammalian brain, are responsible, at least in part, for the low glutamate dehydrogenase activity in vivo. 相似文献
28.
It has long been recognized that the bipedal posture reduces the surface area of the body exposed to the sun. In recent years, a theory has been developed by Wheeler that bipedalism evolved in the ancestor of the Hominidae in order to help relieve thermal stress on the animals in open equatorial environments. Bipedalism was said to afford a distinct adaptive advantage over quadrupedalism by permitting hominids to remain active in the open throughout the day. The heat load of the hypothetical hominid comprises the external environment as modelled by Wheeler and the animal's internal environment (i.e., the internal heat generated by its metabolic and locomotor activities, and its evaporative and respirative cooling capacities). When these factors are integrated in the calculation of the animal's thermal budget, the putative advantage of the bipedal over the quadrupedal posture is considerably reduced. The simulations conducted in this study suggest that the increased time afforded to early hominids in the open by bipedalism was relatively short and, therefore, of little or no adaptive significance. These results suggest that thermoregulatory considerations cannot be implicated as a first cause in the evolution of bipedalism in the hominid ancestor. 相似文献
29.
Autotrophic picoplankton in southern Lake Baikal: abundance, growth and grazing mortality during summer 总被引:5,自引:0,他引:5
Nagata Toshi; Takai Kenji; Kawanobe Kyoko; Kim Dong-Sup; Nakazato Ryoji; Guselnikova Nina; Bondarenko Nina; Mologawaya Oliga; Kostrnova Tatyana; Drucker Valentine; Satoh Yasuhiro; Watanabe Yasunori 《Journal of plankton research》1994,16(8):945-959
Autotrophic picoplankton were highly abundant during the thermalstratification period in late July in the pelagic area (waterdepth 5001300 m) of southern Lake Baikal; maximum numberswere 2 x 106 cells ml1 in the euphotic zone ({small tilde}15m). Unicellular cyanobacteria generally dominated the picoplanktoncommunity, although unidentified picoplankton that fluorescedred under blue excitation were also abundant (maximum numbers4 x 105 cells ml1) and contributed up to {small tilde}40%of the total autotrophic picoplankton on occasions. Carbon andnitrogen biomasses of autotrophic picoplankton estimated byconversion from biovolumes were 1484 µg C l1and 3.621 µg N l1. These were comparableto or exceeded the biomass of heterotrophic bacteria. Autotropicpicoplankton and bacteria accounted for as much as 33% of paniculateorganic carbon and 81% of nitrogen in the euphotic zone. Measurementsof the photosynthetic uptake of [l4C]bicarbonate and the growthof picoplankton in diluted or size-fractionated waters revealedthat 80% of total primary production was due to picoplankton,and that much of this production was consumed by grazers inthe <20 µ.m cell-size category. These results suggestthat picoplankton-protozoan trophic coupling is important inthe pelagic food web and biogeochemical cycling of Lake Baikalduring summer. 相似文献
30.
Kirsi-Marja Oksman-Caldentey Nina Sevón Leena Vanhala Raimo Hiltunen 《Plant Cell, Tissue and Organ Culture》1994,38(2-3):263-272
Abatract The effect of carbon and nitrogen sources on two well-established hairy root clones, LBA1S and C58A, of Hyoscyamus muticus strain Cairo, were investigated. Both clones exhibited completely different patterns with regards to their growth rate, hyoscyamine accumulation, and fatty acid contents. Clone C58A grew faster and yielded more biomass (17.4 g l-1, in 21 days), but produced less hyoscyamine. The maximum hyoscyamine content (120 mg l-1) in clone LBA1S was reached in 28 days. Neither of the clones could use lactose or fructose as the sole carbon source, nor ammonium as the sole nitrogen source. The growth in the medium containing glucose was significantly reduced compared to that containing sucrose. Clone LBA1S was sensitive to the changes in sucrose concentration and an increase in ammonium in the culture medium, whereas C58A tolerated these changes better but was more sensitive to the increase in total nitrogen. Lipid synthesis was active in the exponential growth phase, and the total fatty acid content varied from 5 to 34 mg g-1 of dry root material. The major fatty acids were linoleic, palmitic and linolenic. There were considerable differences in the total amount of lipids and in their relative ratios when different nutrients were applied.Abbreviations DW
dry weight
- FA
fatty acids
- FFA
free fatty acids
- FW
fresh weight 相似文献