精胺和Mg^（2＋）对tRNA^（Ile）圆二向色谱的影响

Effects of Spermine and Mg￣2+ on Circular Dichroism Spectrum of Bovine Liver tRNA￣(Ile)

由于精胺（ｓｐｅｒｍｉｎｅ）能特异地刺激哺乳动物ｔＲＮＡ^（Ｉｌｅ）的氨基酰化，本文用纯化的牛肝ｔＲＮＡ^（Ｉｌｅ）观察了精胺和Ｍｇ（２＋）对ｔＲＮＡ^（Ｉｌｅ）ＣＤ光谱的影响。结果显示：Ｍｇ（２＋）可使牛肝ｔＲＮＡ^（Ｉｌｅ）ＣＤ光谱峰向短波方向偏移２ｎｍ，波峰为２６３ｎｍ，峰值被增大约１０％，ΔθＭｇ（２＋）＝２．３×１０３ｄｅｇ·ｃｍ２／ｄｍｏｌ；而精胺使牛肝ｔＲＮＡ^（Ｉｌｅ）ＣＤ光谱峰减少４０％，Δθｓｐｅｒｍｉｎｅ＝１×１０（－４）ｄｅｇ·ｃｍ２／ｄｍｏｌ；精胺和Ｍｇ（２＋）对肝ｔＲＮＡ^（Ｉｌｅ）－ＩｌｅＲＳ复合物或ＩｌｅＲＳ的ＣＤ光谱基本无影响。表明Ｍｇ（２＋）和精胺可影响牛肝ｔＲＮＡ^（Ｉｌｅ）的构象。实验同时以酵母ｔＲＮＡ（Ｐｈｅ）和Ｅ·ｃｏｌｉｔＲＮＡ^（Ｉｌｅ）作为对照。

In view of the fact that the aminoacylation of mammalian tRNA￣(Ile) can be stimulated by spermine, we observed the effects of spermine and Mg￣(2+) on circular dichroism (CD)spectrum of purified bovine liver tRNA￣(Ile). It showed as follows: 1. In the presence of 5 mmol/L Mg￣(2+), the CD spectrum of bovine liver tRNA￣(Ile) appeared two kinds of alterations:① the positive peak was slightly shifted towards short wavelenth by 2nm, that is, from 265nm to 263nm; ②the amplitude of positive peak at 263nm was increased by about 10% (Δθ= 2. 3×10￣3 deg. cm￣2/dmol); 2. In contrast with effect of Mg￣(2+), the amplitude of positive peak of CD spectrum of bovine liver tRNA￣(Ile) was greatly decreased by about 40% (Δθ= 1×10￣-4 deg.cm￣2/dmol after adding 2 mmol/L spermine. 3. Mg￣(2+) and/or spermine did not change the CD spectra of ether liver IleRS or tRNA￣(Ile)～IleRS complex. These results suggest that both Mg￣(2+) and spermine can affect the conformation of bovine liver tRNA￣(Ile). In the experiment, yeast tRNAr￣(Ile) and E· coli tRNA￣(Ile) were served as control tRNAs.