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In the 1940's several experimental observations were made regarding the K+ and Na+ content of chilled and restored red blood cells. As a consequence, the concept of active transport was developed. Brewer, a physicist, developed a model for membrane transport based on the electrical properties of double bonds in the ground and excited states. Of particular importance is the membrane double bond P = O. This model was largely formulated from isotope concentration studies using mass spectroscopy, photospectrometry and the nature of malignant cells. In this study, it is shown that the Brewer model completely explains the experimental results which led to the concept of active transport. In addition, it also explains the results of some adjunct experiments. 相似文献
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Co-flocculation between cells of beer yeast IFO 2018, a flocculent strain, and non-flocculent strains was investigated by means of a chemical modification method. Treatment with periodate deprived non-flocculent cells, but not flocculent cells, of the ability to co-flocculate. Treatment with mercaptoethanol or photo-irradiation in the presence of methylene blue deprived flocculent cells, but not non-flocculent cells, of the co-flocculating ability. Mercaptoethanol-treated or photoirradiated flocculent cells (beer yeast IFO 2018) co-flocculated with periodate-treated flocculent cells, but periodate-treated cells subsequently subjected to mercaptoethanol treatment or photoirradiation neither flocculated by themselves nor co-flocculated with other cells. Thus, it is likely that both protein and carbohydrate components of the yeast cell surface play important roles in the mutual recognition and intercellular interaction involved in flocculation. It is strongly suggested that the essential carbohydrate which is widely distributed among Saccharomyces species is the mannan fraction on the cell wall, and that a flocculent yeast strain produces surface protein component(s) which recognize and bind the mannan component of adjacent cells. 相似文献
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Brewer spruce (Picea breweriana), a relict of the widespread Arcto-Tertiary forests, is now restricted to a highly fragmented range in the Klamath Region of California and Oregon. Expected heterozygosity for 26 isozyme loci, averaged over 10 populations, was 0.121. More notable than the relatively high level of diversity when compared to other woody endemics was the strong decrease in expected heterozygosity with latitude. Differentiation (F(ST)) was 0.152, higher than values for many north temperate conifers with larger distributions. The number of migrants per generation (Nm) was 1.34 or 2.70, depending on the method of estimation. Inbreeding appeared low; F(IS) was only 0.003, in agreement with multilocus population outcrossing rates (t(m)), which were generally well above 0.90. No difference in t(m) was found between isolated vs. clustered trees. However, the number of seeds per cone was greatest in the densest populations; t(m) is a measure of effective outcrossing after mortality in the embryonic stage, whereas a reduced number of seeds per cone indicates self pollination. Selfing increased after logging; outcrossing rate before logging was 0.961 and after logging, 0.756. Despite Brewer spruce's narrow, fragmented distribution, the outlook for its conservation was good, with the exception of possible negative effects of logging. 相似文献
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Vokes,Richard. Ghosts of Kanungu: fertility,secrecy and exchange in the Great Lakes of East Africa. xvi, 240 pp., maps,illus., bibliogr. Woodbridge,Suffolk: Boydell & Brewer; James Currey, 2009. £55.00 (cloth)
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T.O. Beidelman 《The journal of the Royal Anthropological Institute》2015,21(1):242-243
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Insa Nolte 《The journal of the Royal Anthropological Institute》2020,26(1):193-194
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Emily K. Croteau Stephen C. Lougheed Pamela G. Krannitz Nancy A. Mahony Brett L. Walker Peter T. Boag 《Conservation Genetics》2007,8(6):1453-1463
Assessing the genetic consequences of habitat fragmentation is a crucial step in conservation planning for species in endangered
habitats. We tested for the impact of natural habitat fragmentation on gene flow and genetic diversity in seven northern breeding
locations of the sagebrush Brewer’s sparrow, Spizella breweri breweri. Genetic analyses using five highly variable DNA microsatellite loci suggested that individuals sampled within a sagebrush
landscape fragmented by natural elements such as coniferous forest, comprise a single genetic population and that gene flow
among them is unimpeded. We posit that juvenile dispersal links seemingly isolated breeding locales of this species, and discuss
implications of our findings for conservation of migratory songbirds in the northern portion of their ranges in light of potential
shifts in distribution due to climate change. 相似文献