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101.
Filaggrin is a specific epidermal protein which is the precursor of the free amino acids, urocanic acid and pyrrolidone carboxylic acid which are largely responsible for the ability of the stratum corneum of the skin to remain hydrated at low environmental humidity. The distribution of filaggrin shown by immunofluorescence in the stratum corneum of the rat changed dramatically during the first hours of postnatal life. During late foetal development, filaggrin accumulated through the entire thickness of the stratum corneum, indicating that there was a block on the subsequent processing of the protein which normally would convert it to free amino acids. Immediately after birth this block was lifted and normal proteolysis of the filaggrin took place in the outer part of the stratum corneum, leaving the normal adult pattern of a thin zone of cells containing filaggrin at the bottom of the stratum corneum. This activation of filaggrin proteolysis was dependent on the drop in external water activity caused by the transition from an aqueous environment in utero to a dryer environment after birth and it could be blocked by maintaining a 100% humidity atmosphere around the newborn rat after birth. In isolated stratum corneum in vitro, filaggrin proteolysis took place only between 80 and 95% relative humidity, both higher and lower relative humidity blocked the proteolysis. Application of occlusive patches to adult rats prevented the normal proteolysis of filaggrin, indicating that this mechanism controls not only the massive filaggrin proteolysis occurring after birth but also the proteolysis occurring during normal stratum corneum maturation. The stratum corneum therefore has the ability to respond to changes in external humidity by altering the level of the stratum corneum where it converts its reserves of filaggrin into water binding amino acids, such that under humid conditions water binding components will be produced in only the most superficial stratum corneum, or even not produced at all. 相似文献
102.
H2 evolved by alfalfa root nodules during the process of N2 fixation may be an important factor influencing the distribution of soil bacteria. To test this hypothesis under field conditions, over 700 bacterial isolates were obtained from fallow soil or from the 3-mm layer of soil surrounding alfalfa (Medicago sativa L.) root nodules, alfalfa roots, or bindweed (Convolvulus arvensis L.) roots. Bacteria were isolated under either aerobic or microaerophilic conditions and were tested for their capacity to metabolize H2. Isolates showing net H2 uptake and 3H2 incorporation activity under laboratory conditions were assigned a Hup+ phenotype, whereas organisms with significant H2 output capacity were designated as a Hout+ phenotype. Under aerobic isolation conditions two Hup+ isolates were obtained, whereas under microaerophilic conditions five Hup+ and two Hout+ isolates were found. The nine isolates differed on the basis of 24 standard bacteriological characteristics or fatty acid composition. Five of the nine organisms were isolated from soil around root nodules, whereas the other four were found distributed among the other three soil environments. On the basis of the microaerophilic isolations, 4.8% of the total procaryotic isolates from soil around root nodules were capable of oxidizing H2, and 1.2% could produce H2. Two of the Hup+ isolates were identified as Rhizobium meliloti by root nodulation tests, but the fact that none of the isolates reduced C2H2 under the assay conditions suggested that the H2 metabolism traits were associated with various hydrogenase systems rather than with nitrogenase activity. Results from this study support the concept that H2 evolution by alfalfa root nodules has a significant effect on the surrounding microenvironment and influences the number and diversity of bacteria occupying that region. 相似文献
103.
J N Evans R C Davies A S Boyd I Ichinose N E Mackenzie A I Scott R L Baxter 《Biochemistry》1986,25(4):896-904
High-field NMR spectroscopic methods have been applied to study the reactions catalyzed by porphobilinogen (PBG) deaminase and uroporphyrinogen III (uro'gen III) cosynthase, which are the enzymes responsible for the formation of the porphyrin macrocycle. The action of these enzymes in the conversion of PBG, [2,11-13C]PBG, and [3,5-13C]PBG to uro'gens I and III has been followed by 1H and 13C NMR, and assignments are presented. The principal intermediate that accumulated was the correspondingly labeled (hydroxymethyl)bilane (HMB), the assignments for which are also presented. 相似文献
104.
P M Peters J R Ortaldo M R Shalaby L P Svedersky G E Nedwin T S Bringman P E Hass B B Aggarwal R B Herberman D V Goeddel 《Journal of immunology (Baltimore, Md. : 1950)》1986,137(8):2592-2598
Highly purified populations of large granular lymphocytes (LGL) have been shown to mediate natural killer (NK) cell activity. The mechanism of target cell killing by NK cells is as yet undefined; however, it has been postulated that such killing may involve soluble cytotoxic factors produced and secreted by NK cells. The data presented show that NK-sensitive, but not NK-resistant, tumor cell lines induce highly purified populations of human LGL to produce factors with cytotoxic and/or cytostatic activities. We have identified one of these factors as tumor necrosis factor-alpha (TNF-alpha), and have shown that production of this factor is enhanced by recombinant human interferon-gamma (rHuIFN-gamma). We have also examined the role of TNF-alpha in the cytotoxic function of NK cells. The data show that although highly purified LGL populations produce low levels of TNF-alpha, the cytotoxic/cytostatic activity of this lymphokine on tumor target cells does not correlate with the cytotoxic activity of highly purified populations of LGL on tumor target cells. Furthermore, NK cell-mediated cytotoxicity is not reliably inhibited by antibodies directed against various epitopes of recombinant human TNF-alpha and/or recombinant TNF-beta (lymphotoxin) or rHuIFN-gamma. These data show that although TNF-alpha is produced by highly purified NK-containing LGL cell populations, this factor does not appear to be responsible for NK cell cytotoxicity against classical NK target cells such as Molt-4 or K562. We suggest that NK function can be attributed to a combination of factors rather than to a single factor alone, and that at least two major phenomena are involved in LGL function: the rapid cytotoxic events which lead to the cell lysis measured in classical in vitro NK assays such as against K562; and the release of factors such as TNF-alpha with cytotoxic/cytostatic activities which would inhibit the growth of invading tumor cells in vivo. 相似文献
105.
Summary N2-fixing cyanobacteria occur in symbiotic associations with fungi (ascomycetes) as lichens and with a few green plants. The associated cyanobacterium is always a species ofNostoc orAnabaena. Only a small number of plant genera are involved but there is a remarkable range of host diversity. Associations occur with several bryophytes (e.g.Anthoceros, Blasia, Cavicularia), a pteridophyte (Azolla), cycads (nine genera includingMacrozamia andEncephalartos) and an angiosperm (Gunnera). Except forGunnera, where the cyanobacterium penetrates the plant cells, the cyanobacteria are extracellular with specialized morphological modifications and/or structures of the host plant organs providing an environment which facilitates interaction with the prokaryote.Salient aspects of current knowledge pertaining to the establishment, perpetuation, and functioning of the individual symbioses are summarized. Where possible this includes information concerning recognition and specificity, mode(s) of infection, morphological modifications/adaptations of the host plant and a synopsis of morphological, physiological and biochemical changes common to the symbiotic cyanobacteria. The latter encompasses heterocyst frequencies, enzymes involved in ammonia assimilation, photosynthetic capability and metabolic interaction with the host.TheAzolla-Anabaena symbioses, which have potential agronomic significance as an alternative nitrogen source and maintain continuity with the endophyte through the sexual cycle, are emphasized. 相似文献
106.
A phytase was isolated and partially purified from the pollen of Lilium longiflorum Thumb. Optimum activity was at pH 8.0. The phytase was activated by Ca2+ and Sr2+ but not by the other divalent cations tested. Activity was inhibited by ethylenediaminetetraacetate. The phytase had a temperature optimum of 55 to 60°C and an activation energy of about 12,700 calories/mole. Extraction of L. longiflorum pollen with 0.1% Triton X-100 increased recovery of the phytase by nearly 4-fold. The phytase had a molecular weight of about 88,000 as determined by gel filtration chromatography and a Km value of 7.2 micromolar for phytic acid in the presence of Ca2+. 相似文献
107.
Mechanism of inactivation of rat liver microsomal cytochrome P-450c by 2-bromo-4'-nitroacetophenone 总被引:1,自引:0,他引:1
A Parkinson P E Thomas D E Ryan L D Gorsky J E Shively J M Sayer D M Jerina W Levin 《The Journal of biological chemistry》1986,261(25):11487-11495
The mechanism by which 2-bromo-4'-nitroacetophenone (BrNAP) inactivates cytochrome P-450c, which involves alkylation primarily at Cys-292, is shown in the present study to involve an uncoupling of NADPH utilization and oxygen consumption from product formation. Alkylation of cytochrome P-450c with BrNAP markedly stimulated (approximately 30-fold) its rate of anaerobic reduction by NADPH-cytochrome P-450 reductase, as determined by stopped flow spectroscopy. This marked stimulation in reduction rate is highly unusual in that Cys-292 is apparently not part of the heme- or substrate-binding site, and its alkylation by BrNAP does not cause a low spin to high spin state transition in cytochrome P-450c. Under aerobic conditions the rapid oxidation of NADPH catalyzed by alkylated cytochrome P-450c was associated with rapid reduction of molecular oxygen to hydrogen peroxide via superoxide anion. The intermediacy of superoxide anion, formed by the one-electron reduction of molecular oxygen, established that alkylation of cytochrome P-450c with BrNAP uncouples the catalytic cycle prior to introduction of the second electron. The generation of superoxide anion by decomposition of the Fe2+ X O2 complex was consistent with the observations that, in contrast to native cytochrome P-450c, alkylated cytochrome P-450c failed to form a 430 nm absorbing chromophore during the metabolism of 7-ethoxycoumarin. Alkylation of cytochrome P-450c with BrNAP did not completely uncouple the catalytic cycle such that 5-20% of the catalytic activity remained for the alkylated cytochrome compared to the native protein depending on the substrate assayed. The uncoupling effect was, however, highly specific for cytochrome P-450c. Alkylation of nine other rat liver microsomal cytochrome P-450 isozymes with BrNAP caused little or no increase in hydrogen peroxide formation in the presence of NADPH-cytochrome P-450 reductase and NADPH. 相似文献
108.
Regulation of the terminal event in cellular differentiation: biological mechanisms of the loss of proliferative potential 总被引:11,自引:2,他引:9 下载免费PDF全文
Human plasma has been demonstrated to contain factors that induce the sequential expression of nonterminal and terminal adipocyte differentiation in 3T3 T mesenchymal stem cells. We now report the development of methods for the isolation of purified populations of nonterminally differentiated cells and terminally differentiated cells, and we show that it is possible to experimentally induce transition from the nonterminal to the terminal state of differentiation. With this model system it is therefore now possible to examine the biological and molecular processes associated with the terminal event in differentiation, i.e., the irreversible loss of proliferative potential. In this regard, we demonstrate that transition from the nonterminal to terminal state of differentiation is a complex metabolic process that consists of at least two steps and that this process can be triggered by pulse exposure to an inducer for approximately 12 h but that approximately 24-48 h is required for the process to be completed. The data also establish that induction of the terminal event in differentiation requires protein synthesis but not RNA and DNA synthesis. These and additional results suggest that loss of proliferative potential associated with the terminal event in cellular differentiation is a distinct regulatory process, and we suggest that defects in this regulatory process may be of etiological significance in the pathogenesis of specific human diseases, especially cancer. 相似文献
109.
Specific cell surface insulin binding to embryonic chick neural retina cells has been demonstrated in vivo. Kinetics of insulin binding as well as hormonal specificity were similar to those reported for other vertebrate cells and tissues, both neural and nonneural. When surface insulin binding to retinal cells was studied as a function of embryonic age, a developmental relationship was observed. Scatchard analysis revealed that the number of cell surface insulin receptors decreased approximately 75% between days 10 and 16 of embryonic development. Receptor affinities remained fairly constant for this period. 相似文献
110.
Regulation of the growth of murine B-cell lymphomas has been used as a model for tolerance induction. The inhibition by anti-immunoglobulin reagents of the growth of WEHI-231 and several variant clones has now been studied. The parental line is exquisitely sensitive to growth inhibition by heterologous or monoclonal anti-mu or anti-k reagents and ceases to incorporate thymidine within 24-48 hr of exposure to anti-immunoglobulin reagents. Growth inhibition is initially reversible, but prolonged exposure to anti-mu results in cell death. This inhibition is specific for immunoglobulin light and heavy chains since growth is not inhibited by antibodies directed at either class I or class II histocompatibility antigens. In order to study the mechanism of growth inhibition, we have mutagenized WEHI-231 with ethylmethane sulfonate and cloned the surviving colonies in the presence of anti-mu. Such variants, which have been repeatedly recloned, are able to grow normally in the presence of anti-mu up to 100 micrograms/ml. These "resistant" clones, while expressing amounts of surface IgM similar to that observed on WEHI-231, do not differ markedly in their ability to cap their immunoglobulin receptors compared to the parental line but appear to have lost class II antigens. Cell cycle analysis revealed that anti-mu causes a block in the transition of WEHI-231 from G1 to S phase. The relevance of these processes to models of B-cell tolerance induction are discussed. 相似文献