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161.
Analysis of the nucleotide tightly associated with isolated erythrocyte cytoskeletons show it to be ADP, rather then ATP. This confirms that at least a major part of the erythrocyte actin is in the F-form. A re-evaluation of the stoichiometry of spectrin and actin in the erythrocyte (taking account of a gross difference between the color responses of the two proteins on staining of electrophoretic gels) leads to values of 1x10(5) and 5x10(5) for the number of molecules of spectrin tetramer and actin respectively per cell. It has been found possible to perform spectrophotometric DNAase I assays fro actin on lysed whole cells. The concentration of monomeric actin at 0 degrees C is approximately 16 μg/ml packed cells. After washing the lysed cells the monomer pool is not re-established, indicating that only a small proportion of the actin subunits are free to dissociate. The actin monomer concentration in the cytosol remains unchanged after equilibration of the cells with cytochalasin E. The ability of actin-containing complexes in the membrane to nucleate the polymerization of added G-actin was measured fluorimetrically; it was found that membranes incubated with cytochalasin E were completely inert with respect to nucleating activity under conditions that favor appreciable growth at the slowly-growing (“pointed”) ends of free actin filaments. This suggests that these ends of the actin “protofilaments” in the red cell are blocked or sterically obstructed. After treatment of the membranes with guanidine hydrochloride under conditions that dissociate F-actin, the measured concentration of actin monomer rises to approximately 180 μg/ml of packed cells, which is nearly 70 percent of the total actin content. On treatment with trypsin in the presence of DNAase, the spectrin and 4.1 are extensively degraded, but the actin remains undamaged. This treatment, followed by exposure to guanidine hydrochloride, causes a further rise in the concentration of actin responsive to the DNAase assay to 250 μg/ml of cells, compared with 270 μg/ml estimated by densitometry of stained gels. The oligomeric complex, consisting of actin, spectrin, and 4.1, that is extracted from the membrane at low ionic strength, generates no detectable actin monomer after the same treatment. From literature data on the number of cytochalasin binding sites per cell and our value for the total actin content, we obtain a number-average degree of polymerization for actin in the membrane of 12-17. The results lead to a model for the structure of the cytoskeletal network and suggest some consequences of metabolic depletion. 相似文献
162.
Daniel JC Kronauer Caspar Schöning Lars B Vilhelmsen Jacobus J Boomsma 《BMC evolutionary biology》2007,7(1):56
Background
Army ants are the prime arthropod predators in tropical forests, with huge colonies and an evolutionary derived nomadic life style. Five of the six recognized subgenera of Old World Dorylus army ants forage in the soil, whereas some species of the sixth subgenus (Anomma) forage in the leaf-litter and some as conspicuous swarm raiders on the forest floor and in the lower vegetation (the infamous driver ants). Here we use a combination of nuclear and mitochondrial DNA sequences to reconstruct the phylogeny of the Dorylus s.l. army ants and to infer the evolutionary transitions in foraging niche and associated morphological adaptations. 相似文献163.
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Experiments conducted with rabbit isolated aorta have revealed that the Ca2+-antagonist 3-methoxy-verapamil (D 600) is a potent competitive antagonist of the contractile action of 5-HT. Thus, the anti-hypertensive action of D 600, as well as some of its side effects, could be related to its antagonism of 5-HT receptors. D 600 might be useful in neurochemical and neurophysiological experiments that are aimed at examining 5-HT receptors, as well as in treating certain cerebrovascular disorders of man (e.g., migraine). 相似文献
166.
PCR-based assays of mendelian polymorphisms from anonymous single-copy nuclear DNA: techniques and applications for population genetics 总被引:5,自引:0,他引:5
This paper outlines a PCR-based approach for population genetics that
offers several advantages over conventional Southern blotting methods for
revealing restriction-fragment-length polymorphisms (RFLPs) in nuclear DNA.
Primers are constructed from clones isolated from a nuclear DNA library,
and these primers subsequently are employed in in vitro syntheses of
homologous regions. Amplified products are then screened directly for RFLPs
by using gel-staining procedures. Population applications for this
PCR-based approach, including potential strengths and weaknesses, are
exemplified by two RFLP data sets generated to estimate (a) male-mediated
gene flow in the green turtle (Chelonia mydas) and (b) geographic
population genetic structure in the American oyster (Crassostrea
virginica). Restriction assays of amplified products from 14 or 15
independent primer pairs in each species revealed polymorphisms at several
loci that proved highly informative in the population genetic analyses. In
general, the Mendelian polymorphisms produced by this PCR-based approach
will provide useful genetic markers for population studies, particularly in
situations where simpler and less expensive allozyme methods have failed,
for whatever reason, to provide adequate information.
相似文献
167.
M Auguet M O Lonchampt S Delaflotte J Goulin-Schulz P E Chabrier P Braquet 《FEBS letters》1992,297(1-2):183-185
Inducible vascular nitric oxide synthase accounts for the contractile impairment observed in endotoxemia. We provide evidence that lipoteichoic acid (LTA) from Staphylococcus aureus, a micro-organism without endotoxin, also induces nitric oxide synthase. Our study demonstrates that on endothelium-free rings of rat aorta. LTA-like lipopolysaccharide induces a loss of contractility restored by Methylene blue and NG-nitro-L-arginine-methyl ester (LNAME). Moreover in cultured vascular smooth muscle cells, LTA produces a dose-dependent increase in intracellular cyclic GMP which is antagonized by LNAME and prevented by dexamethasone. 相似文献
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