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41.
Summary The present paper reports the first evidence that homocarnosine-carnosine synthetase from rat brain requires free sulfhydryl groups for activity. The activity of the synthetase can be stabilized by dithioerythritol and inhibited strongly by Cu2+, Cd2+, Hg2+, Zn2+, and to a lesser extent by Ca2+, Ni2+, Li, chlorpromazine, -methyl DOPA and norepinephrine at the concentrations tested.Acknowledgment. This work was supported by United States Public Health Service Grant No. NS-06137. 相似文献
42.
Direct observation of catch bonds involving cell-adhesion molecules 总被引:27,自引:0,他引:27
Bonds between adhesion molecules are often mechanically stressed. A striking example is the tensile force applied to selectin-ligand bonds, which mediate the tethering and rolling of flowing leukocytes on vascular surfaces. It has been suggested that force could either shorten bond lifetimes, because work done by the force could lower the energy barrier between the bound and free states ('slip'), or prolong bond lifetimes by deforming the molecules such that they lock more tightly ('catch'). Whereas slip bonds have been widely observed, catch bonds have not been demonstrated experimentally. Here, using atomic force microscopy and flow-chamber experiments, we show that increasing force first prolonged and then shortened the lifetimes of P-selectin complexes with P-selectin glycoprotein ligand-1, revealing both catch and slip bond behaviour. Transitions between catch and slip bonds might explain why leukocyte rolling on selectins first increases and then decreases as wall shear stress increases. This dual response to force provides a mechanism for regulating cell adhesion under conditions of variable mechanical stress. 相似文献
43.
该报告运用文献计量学方法,对英国及其主要合作伙伴国的国际合作格局做了全面的分析。所选
择的主要国家包括美国、加拿大、法国、德国、日本、澳大利亚、中国与印度;数据覆盖领域有临床、医药
卫生、生物科学、环境科学、数学、物质科学以及工程技术领域;数据时间分为1996-2000年与2001-2005
年两个时间段。结果显示:国际论文数量增长显著;英国国际合作论文份额的增长比G7 国家更加快速; 德
国和美国是英国最大的国际合作伙伴;英国国际合作论文的平均影响力显著高于其科研论文的总体影响力;
中国与英国合作发表的论文数量超过了与其他欧洲各国的合作论文数。 相似文献
择的主要国家包括美国、加拿大、法国、德国、日本、澳大利亚、中国与印度;数据覆盖领域有临床、医药
卫生、生物科学、环境科学、数学、物质科学以及工程技术领域;数据时间分为1996-2000年与2001-2005
年两个时间段。结果显示:国际论文数量增长显著;英国国际合作论文份额的增长比G7 国家更加快速; 德
国和美国是英国最大的国际合作伙伴;英国国际合作论文的平均影响力显著高于其科研论文的总体影响力;
中国与英国合作发表的论文数量超过了与其他欧洲各国的合作论文数。 相似文献
44.
The history of the Parallelogram Rule for composing physical quantities, such as motions and forces, is marked by conceptual difficulties leading to false starts and halting progress. In particular, authors resisted the required assumption that the magnitude and the direction of a quantity can interact and are jointly necessary to represent the quantity. Consequently, the origins of the Rule cannot be traced to Pseudo-Aristotle or Stevin, as commonly held, but to Fermat, Hobbes, and subsequent developments in the latter part of the seventeenth century. 相似文献
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Substantial contribution to sea-level rise during the last interglacial from the Greenland ice sheet 总被引:2,自引:0,他引:2
During the last interglacial period (the Eemian), global sea level was at least three metres, and probably more than five metres, higher than at present. Complete melting of either the West Antarctic ice sheet or the Greenland ice sheet would today raise sea levels by 6-7 metres. But the high sea levels during the last interglacial period have been proposed to result mainly from disintegration of the West Antarctic ice sheet, with model studies attributing only 1-2 m of sea-level rise to meltwater from Greenland. This result was considered consistent with ice core evidence, although earlier work had suggested a much reduced Greenland ice sheet during the last interglacial period. Here we reconsider the Eemian evolution of the Greenland ice sheet by combining numerical modelling with insights obtained from recent central Greenland ice-core analyses. Our results suggest that the Greenland ice sheet was considerably smaller and steeper during the Eemian, and plausibly contributed 4-5.5 m to the sea-level highstand during that period. We conclude that the high sea level during the last interglacial period most probably included a large contribution from Greenland meltwater and therefore should not be interpreted as evidence for a significant reduction of the West Antarctic ice sheet. 相似文献
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