人工合成的酵母丙氨酸转移核糖核酸的生物活力测定

本文报道了用一种高灵敏度的方法测定人工合成的酵母丙氨酸转移核糖核酸(tRNA_y~(Ala))的生物活力。tRNA_y~(Ala)在大鼠肝氨酰基tRNA合成酶的催化下接受丙氨酸后,用操作简便而回收率较高的酒精沉淀法回收氨酰化产物,最后,在兔网织红细胞裂解液无细胞蛋白合成体系中,测定氨酰化产物中的丙氨酸转移到蛋白质中去的能力——参入活力。这方法不仅可以测定分离纯化的tRNA_y~(Ala)的活力,而且也可以测定经T_4RNA连接酶连接两个半分子后的反应混合物中产物tRNA_y~(Ala)的活力。利用这方法,已成功地测定了微至5—7 pmoles的人工全合成tRNA_y~(Ala)的接受活力和参入活力两组数据。测定结果表明,全合成tRNA_y~(Ala)的接受活力是天然分子的51.6—65.6％,是经拆合的天然分子的91.3—106.0％。其氨酰化产物中的[~3H]-Ala在兔网织红细胞裂解液中的利用率为61.6—63.1％,是天然分子的90.6—91.7％,是经拆合的天然分子的97.2—115.8％。     

磁共振波谱技术在吸烟对大脑影响的研究进展

吸烟是导致过早发病和死亡的主要风险因素之一.随着磁共振技术的不断进步,磁共振波谱已成为临床诊断的重要手段之一.与磁共振成像的其他模态一样,磁共振波谱具有无创性的优点,能够反映大脑的神经递质及代谢物的浓度变化情况.吸烟是一个全球性的健康问题,近些年已有一些研究利用磁共振波谱观察吸烟对大脑的影响.针对这一广泛关注的社会问题,本文对吸烟人群的磁共振波谱研究进展进行了综述,总结了烟草对大脑代谢的影响.本综述为深入研究烟草依赖的神经生物学机制提供了新的视角,从技术层面为早期诊断、治疗及预防吸烟对大脑的负面影响提供了支持.     

ASSAY OF BIOLOGICAL ACTIVITY OF SYNTHETIC YEAST ALANINE TRANSFER RNA (tRNA_y~(Ala))

The biological activity of the synthetic tRNA_y~(Ala) was studied with an extremely sensitive method, tRNA_y~(Ala). accepted alanine in the presence of rat liver aminoacyl-tRNA_y~(Ala)-synthetase (this was called the accepting actvity). The aminoacylated tRNA_y~(Ala) was conveniently precipitated by ethanol with good recovery. The efficiency of transferring alanine from the aminoacylated tRNA_y~(Ala) into the protein was determined in in vitro rabbit reticulocyte lysate cell-free protein-synthesizing system (this was called the incorporation activity). Both accepting and incorporation activities could be determined in one assay with only 5-7 pmoles of tRNA_y~(Ala) either in ligation mixture or in purified form.Our results show that the accepting activities of the synthetic products were 51.6-65.6% and 91.3-106.0% of that of natural and reconstituted natural tRNA_y~(Ala) respectively. The efficiency of the incorporation of alanine in the aminoacylated tRNA_y~(Ala) into the protein was 61.6-63.1%, corresp