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911.
Résumé Le cytoplasme du foie de têtard contient une enzyme qui hydrolyse spécifiquement les protéines basiques telle que la polylysine, la protamine et les histones. L'addition d'autres protéines telles que l'albumine, la globuline et l'acide polyglutamique inhibe l'activité de cette enzyme. Les résultats obtenus montrent que cette hydrolysase extraite du foie de têtard diffère des cathépsines ou de l'histone-hydrolase du rein de rat.
This work was supported by research grants from the National Institute of Arthritis and Metabolic Diseases No. AM 09602, National Science Foundation No. GB-22663 and from the National Cancer Institute No. CA 07174. 相似文献
This work was supported by research grants from the National Institute of Arthritis and Metabolic Diseases No. AM 09602, National Science Foundation No. GB-22663 and from the National Cancer Institute No. CA 07174. 相似文献
912.
913.
Mitotic cycles in dicotyledons and monocotyledons 总被引:1,自引:0,他引:1
914.
Detection of human leukaemia associated antigens in leukaemic serum and normal embryos 总被引:4,自引:0,他引:4
R Harris D Viza R Todd J Phillips R Sugar R F Jennison G Marriott M H Gleeson 《Nature》1971,233(5321):556-557
915.
Crystallization of a second adenovirus protein (the fibre) 总被引:5,自引:0,他引:5
916.
917.
T H Benzinger 《Nature》1971,229(5280):100-102
918.
919.
The geochemical composition of the Earth's upper mantle is thought to reflect 4.5 billion years of melt extraction, as well as the recycling of crustal materials. The fractionation of rhenium and osmium during partial melting in the upper mantle makes the Re-Os isotopic system well suited for tracing the extraction of melt and recycling of the resulting mid-ocean-ridge basalt. Here we report osmium isotope compositions of more than 700 osmium-rich platinum-group element alloys derived from the upper mantle. The osmium isotopic data form a wide, essentially gaussian distribution, demonstrating that, with respect to Re-Os isotope systematics, the upper mantle is extremely heterogeneous. As depleted and enriched domains can apparently remain unequilibrated on a timescale of billions of years, effective equilibration seems to require high degrees of partial melting, such as occur under mid-ocean ridges or in back-arc settings, where percolating melts enhance the mobility of both osmium and rhenium. We infer that the gaussian shape of the osmium isotope distribution is the signature of a random mixing process between depleted and enriched domains, resulting from a 'plum pudding' distribution in the upper mantle, rather than from individual melt depletion events. 相似文献
920.
Quantifying nitrogen-fixation in feather moss carpets of boreal forests 总被引:21,自引:0,他引:21
Biological nitrogen (N) fixation is the primary source of N within natural ecosystems, yet the origin of boreal forest N has remained elusive. The boreal forests of Eurasia and North America lack any significant, widespread symbiotic N-fixing plants. With the exception of scattered stands of alder in early primary successional forests, N-fixation in boreal forests is considered to be extremely limited. Nitrogen-fixation in northern European boreal forests has been estimated at only 0.5 kg N ha(-1) yr(-1); however, organic N is accumulated in these ecosystems at a rate of 3 kg N ha(-1) yr(-1) (ref. 8). Our limited understanding of the origin of boreal N is unacceptable given the extent of the boreal forest region, but predictable given our imperfect knowledge of N-fixation. Herein we report on a N-fixing symbiosis between a cyanobacterium (Nostoc sp.) and the ubiquitous feather moss, Pleurozium schreberi (Bird) Mitt. that alone fixes between 1.5 and 2.0 kg N ha(-1) yr(-1) in mid- to late-successional forests of northern Scandinavia and Finland. Previous efforts have probably underestimated N-fixation potential in boreal forests. 相似文献