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51.
52.
Walter R. Stahl 《Bulletin of mathematical biology》1961,23(4):355-376
Dimensional analysis is discussed from the viewpoint of its basic group properties and shown to be an algebraic Abelian group
that is useful for analysis of physical measurements. The application of the method to various types of equations and the
formulation of previously unclassified dimensions are discussed. Functional dimensional analysis is applied to the problems
of cell size and biomass proliferation; future applications are also noted. A number of dimensionless terms have been formulated
for cellular physiochemical phenomena. They apparently represent the first systematic study of biological dimensionless numbers
recorded in the literature. A dimensionless proliferation law is suggested. A brief analysis of the physical dimensionality
associated with information measures is carried out. Entropy and “information” are shown to be completely different in their
dimensional meaning; other informational measures of possible interest in biology are proposed. The dimensional coding and
computor analysis of biomathematical equations is suggested. 相似文献
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GTP gamma S stimulation of endosome fusion suggests a role for a GTP-binding protein in the priming of vesicles before fusion. 总被引:7,自引:1,他引:6 下载免费PDF全文
Guanosine 5'-(3-O-thio)triphosphate (GTP gamma S), a non-hydrolyzable analogue of GTP, inhibits in vitro fusion among early endocytic vesicles in the presence of high concentrations of cytosol. In this report we show that fusion is remarkably stimulated by GTP gamma S under conditions where cytosolic components are the limiting factors for the process. The amount of cytosolic factors required for maximal fusion activity is several-fold decreased by the presence of GTP gamma S. Moreover, preincubation of vesicles in the presence of cytosol and GTP gamma S allows fusion to proceed even in the absence of cytosol. Our results indicate that a GTP-binding protein facilitates the binding of cytosolic factor(s) required for endosome fusion to the endosomal membrane and stabilizes a dilution-resistant intermediate of the fusion process. 相似文献
57.
The presence of acid proteases in the endosomal compartment of macrophages has been recently demonstrated (Diment, S., Leech, M. S., and Stahl, P. D. (1988) J. Biol. Chem. 263, 6901-6907). This proteolytic activity allows the early degradation of ligands internalized by receptor-mediated endocytosis. To study the early steps that initiate the proteolytic processing of ligands, immune complexes formed with anti-dinitrophenol monoclonal IgG and radiolabeled dinitrophenol-derivatized bovine serum albumin were bound at 4 degrees C to Fc receptors of J774 macrophages. Cells were allowed to internalize immune complexes bound to the plasma membrane for different periods of time at 37 degrees C. Vesicle preparations generated from these cells were incubated in vitro at acidic pH to allow the hydrolysis of ligands located in protease-positive compartments. Ligand hydrolysis was observed after about 5 min of internalization, suggesting that at earlier times immune complexes were located in protease-free vesicles. Upon incubation of cell lysates under conditions that support in vitro endosome-endosome fusion, early protease-free endosomes containing ligand acquire proteolytic activity. Reconstitution of fusion-dependent proteolysis required energy, ions, membrane-associated factors, and cytosol. Cytosol was inactivated by incubation with N-ethylmaleimide. The proteolytic compartment formed upon in vitro incubation colocalized with endosomes in the light region of a Percoll gradient. Reconstitution was also achieved using an endosomal preparation separated from lysosomes in a Percoll gradient. Our results indicate that a fusion step between newly formed endocytic vesicles and a light density, protease-positive compartment triggers the proteolytic processing of ligands internalized by receptor-mediated endocytosis. 相似文献
58.
Rennenberg H Huber B Schröder P Stahl K Haunold W Georgii HW Slovik S Pfanz H 《Plant physiology》1990,92(3):560-564
Spruce (Picea Abies L.) trees from the same clone were supplied with different, but low, amounts of plant available sulfate in the soil (9.7-18.1 milligrams per 100 grams of soil). Branches attached to the trees were enclosed in a dynamic gas exchange cuvette and analyzed for the emission of volatile sulfur compounds. Independent of the sulfate supply in the soil, H2S was the predominant reduced sulfur compound continuously emitted from the branches with high rates during the day and low rates in the night. In the light, as well as in the dark, the rates of H2S emission increased exponentially with increasing water vapor flux from the needles. Approximately 1 nanomole of H2S was found to be emitted per mole of water. When stomata were closed completely, only minute emission of H2S was observed. Apparently, H2S emission from the needles is highly dependent on stromatal aperture, and permeation through the cuticle is negligible. In several experiments, small amounts of dimethylsulfide and carbonylsulfide were also detected in a portion of the samples. However, SO2 was the only sulfur compound consistently emitted from branches of spruce trees in addition to H2S. Emission of SO2 mainly proceeded via an outburst starting before the beginning of the light period. The total amount of SO2 emitted from the needles during this outburst was correlated with the plant available sulfate in the soil. The diurnal changes in sulfur metabolism that may result in an outburst of SO2 are discussed. 相似文献
59.
Dual staining of natural bacterioplankton with 4',6-diamidino-2-phenylindole and fluorescent oligonucleotide probes targeting kingdom-level 16S rRNA sequences. 总被引:8,自引:6,他引:2 下载免费PDF全文
A method for quantifying eubacterial cell densities in dilute communities of small bacterioplankton is presented. Cells in water samples were stained with 4',6-diamidino-2-phenylindole (DAPI), transferred to gelatin-coated slides, and hybridized with rhodamine-labeled oligonucleotide probes specific for kingdom-level 16S rRNA sequences. Between 48 and 69% of the cells captured on membrane filters were transferred to gelatin-coated slides. The number of DAPI-stained cells that were visualized with eubacterial probes varied from 35 to 67%. Only 2 to 4% of these cells also fluoresced following hybridization with a probe designed to target a eukaryotic 16S rRNA sequence. Between 0.1 and 6% of the bacterioplankton in these samples were autofluorescent and may have been mistaken as cells that hybridized with fluorescent oligonucleotide probes. Dual staining allows precise estimates of the efficiency of transfers of cells to gelatin films and can be used to measure the percentage of the total bacterioplankton that also hybridize with fluorescent oligonucleotide probes, indicating specific phylogenetic groups. 相似文献
60.
Hoch Brigitte Lutsch Gudrun Schlegel Wolfgang-Peter Stahl Joachim Wallukat Gerd Bartel Sabine Krause Ernst-Georg Benndorf Rainer Karczewski Peter 《Molecular and cellular biochemistry》1996,160(1):231-239
Recent investigations concentrate on the correlation between the myocardial expression of the inducible 70-kDa heat shock protein (HSP70i) by different stress conditions and its possible protective effects. Only few studies have focused on the involvement of small heat shock proteins in this process. We analyzed the location of the small heat shock protein HSP25 in isolated cardiomyocytes as well as its location and induction in isolated perfused hearts of rats. By immunofluorescence microscopy HSP25 was found to colocalize with actin in the I-band of myofibrils in cardiomyocytes of isolated perfused hearts as well as in isolated neonatal and adult cardiomyocytes. Hyperthermic perfusion of isolated hearts for 45 min resulted in modulation of different parameters of heart function and in induction of HSP25 and HSP70i. Temperatures higher than 43°C (44–46°C) were lethal with respect to the contractile function of the hearts. Compared to control hearts perfused at 37°C, significant increases during hyperthermic perfusion at 42°C and 43°C were obtained for heart rate, contraction velocity and relaxation velocity. In response to hyperthermia at 43°C and after subsequent normothermic perfusion for 135 min at 37°C, left ventricular pressure, contraction velocity and relaxation velocity remained significantly elevated. However, heart rate returned to control values immediately after the period of heat treatment. HSP25 is constitutively expressed even in normothermic perfused hearts as shown by Western blotting. Hyperthermia increased the content of HSP25 only in the left ventricular tissue. In contrast, HSP70i was strongly induced in all analyzed parts of the myocardium (left ventricle, right ventricle, septum). Our findings suggest a differential regulation of HSP25 and HSP70i expression in response to hyperthermia in isolated perfused hearts. The constitutively expressed HSP25 seems to be located adjacent to the myofibrils which implies a specific role of this protein even under unstressed conditions for the contractile function of the myocardium. 相似文献