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921.
Degradation of ornithine decarboxylase: exposure of the C-terminal target by a polyamine-inducible inhibitory protein. 总被引:11,自引:1,他引:10
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Polyamine-mediated degradation of vertebrate ornithine decarboxylase (ODC) is associated with the production of antizyme, a reversible tightly binding protein inhibitor of ODC activity. The interaction of antizyme with a binding element near the N terminus of ODC is essential but not sufficient for regulation of the enzyme by polyamines (X. Li and P. Coffino, Mol. Cell. Biol. 12:3556-2562, 1992). We now show that a second element present at the C terminus is required for the degradation process. Antizyme caused a conformational change in ODC, which made the C terminus of ODC more accessible. Blocking the C terminus with antibody prevented degradation. Tethering the C terminus by creating a circularly permuted, enzymatically active form of ODC prevented antizyme-mediated degradation. These data elucidate a form of feedback regulation whereby excess polyamines induce destruction of ODC, the enzyme that initiates their biosynthesis. 相似文献
922.
923.
924.
Masato Maekawa Kayoko Sudo Masato Kitajima Yukio Matsuura Steven S.-L. Li Takashi Kanno 《Human genetics》1993,92(2):163-168
In northwest European countries maternal age is increasing. This will lead to an increase of the prevalence of Down syndrome conceptuses. Meanwhile, the increased use of prenatal cytogenetic diagnosis (PCD) will lead to a decrease in the prevalence of Down syndrome among livebirths. We were interested to know what the result of these two opposite developments would be in the near future, and we describe here a model to quantify these processes and the resulting livebirth prevalence of Down syndrome. The model is demonstrated for The Netherlands from 1992 to 2001. The predicted livebirth prevalence for The Netherlands in 1992 is 1.36 per 1000. Demographic factors will cause an increase to 1.76 per 1000 in 2001 with present indications for PCD and a utilization ratio of 50%. An increase of the utilization ratio to 90% in 2001 will lead to a prevalence of 1.22 per 1000, a little less than the present prevalence. Alternative screening programs, including maternal serum screening, could lead to a further decrease of the livebirth prevalence. The model described here can be used for evaluation of the consequences of alternative forms of Down syndrome screening. 相似文献
925.
本文对蛋白质中二硫键附近的残基进行了计算机统计分析,结果发现平行和反平行残基间存在着特异的配对规律。这种残基间的相互作用或识别,可能与蛋白质折叠过程中正确地形成二硫键有关。该结果有助于蛋白质工程设计。 相似文献
926.
本研究在改进后短程序基础上,对氨基酸分离柱进行了改进。改进后的分离柱长为10cm。比原来20cm长柱分离3—MH的时间缩短了近1/2。实验所得的(回收率为97.59%,分离度0.89±0.02。变异系数1.17)这些指标较国外用其它方法所得的结果有良好的相关性。多次测定结果说明长柱与短柱比较无明显差异。证明了短柱对3—MH含量无影响。这一改进所建立的方法大大地缩短了样品的分析时间,节约了大量进口试剂,开展这方面的工作将有利益提高严重烧伤、创伤后蛋白质代谢和营养学等方面的研究水平。 相似文献
927.
本文报导了薄层层析法及高压液相色谱法定性定量地测定植物油甘油酯的组成,对不同来源的脂肪酶对植物油的水解进行了研究。实验结果表明,不同来源的脂肪酶对植物油(橄榄油)的水解性不同,同一脂肪酶水解不同种类的植物油,脂肪酶的水解率也不同,脂肪酶水解植物油有最适pH和最适温度。 相似文献
928.
本文研究了小鼠腹腔巨噬细胞对正常人极低密度脂蛋白(N-VLDL)两种亚组分VLDL_1和VLDL_3的代谢。两种亚组分都能以受体方式和非特异性方式被巨噬细胞摄取和降解。在受体途径中以VLDL_1的摄入量居多。对胞内甘油三酯(TG)的堆积作用以VLDL_1较强,对胆固醇酶(CE)的堆积则以VLDL_3较强。表明两者在促进巨噬细胞向泡沫细胞转变中的作用有所不同。 相似文献
929.
Elevated tropospheric ozone (O3) affects the allocation of biomass aboveground and belowground and influences terrestrial ecosystem functions. However, how belowground functions respond to elevated O3 concentrations ([O3]) remains unclear at the global scale. Here, we conducted a detailed synthesis of belowground functioning responses to elevated [O3] by performing a meta-analysis of 2395 paired observations from 222 publications. We found that elevated [O3] significantly reduced the primary productivity of roots by 19.8%, 16.3%, and 26.9% for crops, trees and grasses, respectively. Elevated [O3] strongly decreased the root/shoot ratio by 11.3% for crops and by 4.9% for trees, which indicated that roots were highly sensitive to O3. Elevated [O3] impacted carbon and nitrogen cycling in croplands, as evidenced by decreased dissolved organic carbon, microbial biomass carbon, total soil nitrogen, ammonium nitrogen, microbial biomass nitrogen, and nitrification rates in association with increased nitrate nitrogen and denitrification rates. Elevated [O3] significantly decreased fungal phospholipid fatty acids in croplands, which suggested that O3 altered the microbial community and composition. The responses of belowground functions to elevated [O3] were modified by experimental methods, root environments, and additional global change factors. Therefore, these factors should be considered to avoid the underestimation or overestimation of the impacts of elevated [O3] on belowground functioning. The significant negative relationships between O3-treated intensity and the multifunctionality index for croplands, forests, and grasslands implied that elevated [O3] decreases belowground ecosystem multifunctionality. 相似文献
930.
Hui Yang Seth M. Munson Chris Huntingford Nuno Carvalhais Alan K. Knapp Xiangyi Li Josep Peñuelas Jakob Zscheischler Anping Chen 《Global Change Biology》2023,29(8):2351-2362
Negative extreme anomalies in vegetation growth (NEGs) usually indicate severely impaired ecosystem services. These NEGs can result from diverse natural and anthropogenic causes, especially climate extremes (CEs). However, the relationship between NEGs and many types of CEs remains largely unknown at regional and global scales. Here, with satellite-derived vegetation index data and supporting tree-ring chronologies, we identify periods of NEGs from 1981 to 2015 across the global land surface. We find 70% of these NEGs are attributable to five types of CEs and their combinations, with compound CEs generally more detrimental than individual ones. More importantly, we find that dominant CEs for NEGs vary by biome and region. Specifically, cold and/or wet extremes dominate NEGs in temperate mountains and high latitudes, whereas soil drought and related compound extremes are primarily responsible for NEGs in wet tropical, arid and semi-arid regions. Key characteristics (e.g., the frequency, intensity and duration of CEs, and the vulnerability of vegetation) that determine the dominance of CEs are also region- and biome-dependent. For example, in the wet tropics, dominant individual CEs have both higher intensity and longer duration than non-dominant ones. However, in the dry tropics and some temperate regions, a longer CE duration is more important than higher intensity. Our work provides the first global accounting of the attribution of NEGs to diverse climatic extremes. Our analysis has important implications for developing climate-specific disaster prevention and mitigation plans among different regions of the globe in a changing climate. 相似文献