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91.
Release of spectrin-free vesicles from human erythrocytes during ATP depletion: 1. characterization of spectrin-free vesicles 总被引:1,自引:0,他引:1
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Human erythrocytes incubated without glucose at 37 degrees C (in vitro aging) release spectrin-free vesicles after 12 or more hours. The release of vesicles is dependent upon ATP depletion. If the endogenous level of ATP is maintained, vesicle release is completely inhibited up to 54 h. Vesicle release is independent of hemolysis because in vitro aged cells and cells that maintain their ATP levels lose identical amounts of hemoglobin up to 45 h. 93 percent of all membrane particles released constitute a uniform population of spheres with a diameter of 185 +/- 23nm. These vesicles are of slightly varying densities due to varying contents of hemoglobin. Vesicles contain half the amount of membrane protein that is found in intact membranes when referred to the content of phospholipids phosphorus. This is primarily due to the absence of spectrin. However, their content of protein component III, glycophorin, and cholesterol remains the same as in intact membranes. Thus, the major integral membrane proteins are present in vesicles in similar quantities were surface area as in cells except for the enzyme acetylcholinesterase that is enriched up to twofold. The phospholipids composition of these vesicles is representative of the intact membrane except that the amount of phosphatidic acid is 10-fold higher and the amount of phosphatidylethanolamine is slightly lower than in erythrocytes. These results suggest a selective release of membrane domains that lack peripheral membrane proteins and are enriched in acetylcholinesterase. This release of spectrin-free vesicles from cells aged in vitro could represent an acceleration of the physiological aging process. 相似文献
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J. F. G. Wheeler D.SC F.L.S. F. A. Brown Jun. Ph.D. 《Zoological Journal of the Linnean Society》1936,39(267):413-428
Observations from the jetty of the Biological Station, Bermuda, of the appearance of Anchistioides antiguensis (Schmitt) at the surface over a short period in 1934 and eight months in 1935 are recorded, and show definite periodicity sometimes of sufficient intensity to merit the term swarming.
The periodicity coincides with the two weeks of the lunar cycle when the moon wanes from the last quarter to the first quarter of the new cycle. It appears to consist of two maximum appearances separated by an interval of some days.
Direct lunar influence, sex and the reproductive period, the surface-temperature, wind and weather, and the state of the tide are shown to have no connexion with swarming.
An explanation is suggested based on the feeding habits and depending on the periodic activity of the worms that form the food. The double maximum of the swarming period is shown to represent two stages of growth. 相似文献
The periodicity coincides with the two weeks of the lunar cycle when the moon wanes from the last quarter to the first quarter of the new cycle. It appears to consist of two maximum appearances separated by an interval of some days.
Direct lunar influence, sex and the reproductive period, the surface-temperature, wind and weather, and the state of the tide are shown to have no connexion with swarming.
An explanation is suggested based on the feeding habits and depending on the periodic activity of the worms that form the food. The double maximum of the swarming period is shown to represent two stages of growth. 相似文献
100.
Positive selection and the molecular evolution of a gene of male reproduction, Acp26Aa of Drosophila 总被引:4,自引:1,他引:3
The gene for a male ejaculatory protein, Acp26Aa, in four sibling species
of the Drosophila melanogaster subgroup has previously been shown to have a
nonsynonymous rate (Ka) of nucleotide substitution that is
indistinguishable from the synonymous rate (Ks). By examining this gene in
two other species of this subgroup, we found that Ka is generally large and
can sometimes be more than twice as large as Ks. This suggests that
positive selection may be operating at this locus of male reproduction.
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