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Rabbit alveolar macrophages exhibit a chemiluminescent response which is associated with phagocytosis of zymosan and polystyrene-butadiene particles. The chemiluminescence reaches a peak in 15 to 25 minutes and then gradually diminishes over the next 1 to 3 hours. During the time of maximal light emission there appears to be no actual uptake of particles, but the response is dependent upon the particle concentration. The metabolic inhibitor, DNP (2,4-dinitrophenol), causes a rapid inhibition of the chemiluminescent response. The addition of ATP to the medium prior to exposure of the cells to particles causes the chemiluminescent response to be greatly diminished, i.e., 0.3mM ATP virtually abolishes the response. These experiments suggest that some metabolic response of the cell to phagocytosis is responsible for the chemiluminescence. 相似文献
114.
Thomas Bell Michael B. Bonsall Angus Buckling Andrew S. Whiteley Timothy Goodall Robert I. Griffiths 《Biology letters》2010,6(5):639-642
Productivity and predation are thought to be crucial drivers of bacterial diversity. We tested how the productivity–diversity of a natural bacterial community is modified by the presence of protist predators with different feeding preferences. In the absence of predators, there was a unimodal relationship between bacterial diversity and productivity. We found that three protist species (Bodo, Spumella and Cyclidium) had widely divergent effects on bacterial diversity across the productivity gradient. Bodo and Cyclidium had little effect on the shape of the productivity–diversity gradient, while Spumella flattened the relationship. We explain these results in terms of the feeding preferences of these predators. 相似文献
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U A Bommer G Lutsch J Behlke J Stahl N Nesytova A Henske H Bielka 《European journal of biochemistry》1988,172(3):653-662
The location of initiation factor eIF-2 and of its subunits in quaternary initiation complexes (40S-ribosomal-subunit.eIF-2. GuoPP[CH2]P.Met-tRNAf) was investigated by immunoelectron microscopy. Quaternary complexes were fixed with glutaraldehyde and reacted with affinity-purified polyclonal antibodies against eIF-2 alpha, eIF-2 beta or eIF-2 gamma. The dimeric immune complexes obtained by sucrose gradient centrifugation were investigated electron microscopically after negative staining. Antibody-binding sites were observed on the interface side of the 40S ribosomal subunit in the region between the 'head' and the 'body' (neck region) of the 40S ribosomal subunit. Within this region, eIF-2 alpha points to the rear side, whereas eIF-2 beta and eIF-2 gamma point to the frontal side of the 40S subunit indicating an elongated shape of eIF-2 about 15 nm long. By analytical ultracentrifugation of isolated eIF-2 the sedimentation and diffusion coefficients were determined to be 6.54 S and 4.74 x 10(-7) cm2/s respectively. From these data, a molar mass of 122.4 kg/mol and a dry volume of 147.4 nm3 were calculated. For the shape of eIF-2 a prolate ellipsoid of revolution is assumed with a maximal length of about 15 nm and with an axial ratio of about 1:3.5. This conclusion is further confirmed by a calculated frictional ratio of 1.37 and a Stokes radius of about 4.54 nm. 相似文献
118.
Rpn1 (109 kDa) and Rpn2 (104 kDa) are components of the 19S regulatory complex of the proteasome. The central portions of both proteins are predicted to have toroidal α-solenoid folds composed of 9-11 proteasome/cyclosome repeats, each ∼ 40 residues long and containing two α-helices and turns [A. V. Kajava, J. Biol. Chem. 277, 49791-49798, 2002]. To evaluate this prediction, we examined the full-length yeast proteins and truncated versions thereof consisting only of the repeat-containing regions by gel filtration, CD spectroscopy, and negative-staining electron microscopy (EM). All four proteins are monomeric in solution and highly α-helical, particularly the truncated ones. The EM data were analyzed by image classification and averaging techniques. The preponderant projections, in each case, show near-annular molecules 6-7 nm in diameter. Comparison of the full-length with the truncated proteins showed molecules similar in size and shape, indicating that their terminal regions are flexible and thus smeared to invisibility in the averaged images. We tested the toroidal model further by calculating resolution-limited projections and comparing them with the EM images. The results support the α-solenoid model, except that they indicate that the repeats are organized not as symmetrical circular toroids but in less regular horseshoe-like structures. 相似文献
119.
Michael A. Fox 《Bulletin of mathematical biology》1973,35(1-2):11-17
Complexity and stability are the ubiquitous characteristics of all biological phenomena. The theoretical suggestions presented
here acknowledge this and attempt to capitalize on the property of selectiveness that complexity induces. It is from this
that a belief in the existence of selection rules emerges. What is required of a viable theory is a linguistic means of maneuvering
known information so that these selection or limitation rules may be obtained, and thence, by their manipulation, to generate
the properties exhibited by biological systems. 相似文献
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