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61.
62.
Ultrastructural localization of the high molecular weight proteins associated with in vitro-assembled brain microtubules 总被引:51,自引:30,他引:21
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Microtubules isolated from brain extracts by in vitro assembly (1, 19, 23) are composed principally of two tubulins and two high molecular weight proteins (microtubule-associated proteins [MAPS] 1 and 2) (2,5,7,20). Recently, it was demonstrated that in vitro-assembled brain microtubules (neurotubules) are coated with filaments (5, 7) which are similar to the filaments attached to neurotubules in situ (4, 15, 21, 24, 25), and it was suggested that the filaments are composed of the higher molecular weight MAPs (5, 7, 12). In this study, microtubules were assembled in the presence and absence of the MAPs, and thin sections of the microtubules were examined by electron microscopy. The results show that the filaments only occur on microtubules assembled in the presence of the MAPs and it is therefore concluded that the filaments are composed of the high molecular weight MAP's. 相似文献
63.
Phleomycin (=2 mug/ml) induces neither deoxyribonucleic acid (DNA) breakdown nor cell death in stationary-phase Escherichia coli B cells, but the addition of 8 mm caffeine immediately initiates these changes in the same way as increasing the phleomycin concentration 10-fold. This phenomenon is termed "amplification" (6). Pyronin Y, a number of nontoxic thio- and mercaptopurines (of which the most active were 6,7- and 6,9-dimethyl-2-methylthiopurine), and coumarin have been found to be considerably more efficient amplifiers of phleomycin activity than caffeine. Thus 2 mm 6,7- and 6,9-dimethyl-2-methylthiopurine, 0.16 mm pyronin, and 4 mm coumarin killed 10 to 100 times more phleomycin-treated bacteria within 2 hr than 8 mm caffeine. As with caffeine, amplification of cell death by these compounds was accompanied by degradation of DNA to acid-soluble fragments. A number of compounds including 2,6-dichloropurine, 6-hydroxy-2-methylthiopurine, alpha-naphthol, beta-naphthol, naphthionic acid, and alpha-naphthol-4,8-disulphonic acid inhibited the action of phleomycin, if they were present in the cell suspension during phleomycin treatment, but some caused amplification if added subsequent to the phleomycin. Although no mutants resistant to >/=10 mug of phleomycin per ml were observed among 10(11)E. coli B cells screened, such mutants occurred with a frequency of 10(-6) to 10(-7) among cultures resistant to 1 to 2 mug of phleomycin per ml. These double mutants were cross-resistant to phleomycin plus caffeine. The amplifying compounds, though structurally dissimilar, shared the common characteristic of binding selectively to denatured DNA as measured by equilibrium dialysis methods. The implications of these observations in supporting a model of phleomycin amplification proposed previously (6) and their utility in providing a logic for developing a new class of antibiotics are discussed. 相似文献
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Intracavernous injection of 20 μg of prostaglandin E1 (PGE1) was carried out in 130 impotent patients. The erectile response was compared to the results of arteriological investigations including nocturnal penile tumescence and rigidity monitoring (NPTR) in 59 patients. The response of 60 patients positively categorized as exclusively psychogenic or vasculogenic was also compared to the pattern of the response to 80 mg of papaverine observed in a previous study by the same authors. The PGE1 test may not discriminate psychogenic from wholly organic patients since its results are not correlated to those of NPTR. It helps for the screening of vasculogenic impotence. Lack of response or a partly rigid response is consistent with this actiology but is not specific for it. A fully response makes it unlikely. Compared to papaverine, PGE1 induces less non rigid responses in psychogenic patients (15% versus 35% with papaverine) and more fully rigid responses in vasculogenic patients (respectively 12% and 5 %). Consequently the specificity of the PGE1 test is higher but its sensitivity lower than that of papaverine so that there is no clear difference in the effectiveness of the tests. Nevertheless the PGE1 test should be preferred, because it is safer. Prolonged erections occured in only 5 patients, and all ceased spontaneously. However 4 presented severely painful erections. 相似文献
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An acinus is the principal secretion unit of an exocrine gland. This paper sets up a mathematical model of an acinus and examines the effect on the output of varying the operating parameters, both of the secretion mechanism and the fluid properties. Particular reference is made to acini of the pancreas. The question of whether the effects of cystic fibrosis on the pancreas can be attributed to the increased viscosity of the exudate is also considered. The work identifies key parameters, and their quantitative ranges, which would need to be examined experimentally in order to resolve this question. 相似文献
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Survival and growth of hatchling Crocodylus porosus in saltwater without access to fresh drinking water 总被引:1,自引:0,他引:1
Summary It has been suggested that C. porosus select nest sites which provide a source of freshwater for hatchlings during the dry season. From a mark-recapture study, we conclude that hatchling C. porosus can survive and grow in hyperosmotic saltwater without drinking freshwater. Hence, the siting of nests is unlikely to be the consequence of a requirement by hatchlings for freshwater. Considered along with other information, our observations imply that hatchling C. porosus have functional salt glands. 相似文献