Experimental Approach for the Molecular Recognition Mechanism of Amino Acids by Complex of Four Nucleotides on tRNA

分子构筑和半经验计算表明，由三个反密码子碱基和一个基于tRNA的鉴别子组成的四个核苷酸(C4N)的复合体上有一个口袋，可以接受同源氨基酸。这种关系可能是遗传密码的分子基础。我们尝试用紫外吸收、荧光和圆二色谱等三种光谱方法来检测tRNA(或寡核苷酸)与氨基酸的特异性相互作用：在C4N模型中，可以预测&lt；tRNA^(Asp)&gt；和&lt；tRNA^(Glu)&gt；可以在没有鉴别碱基的情况下区分它们的同源氨基酸，而&lt；tRNA^(Phe)&gt；则不能。&lt；tRNA^(Asp)&gt；和&lt；tRNA^(Glu)&gt；分别以queosine和mn&lt；m^5&gt；&lt；S^2&gt；U为其第一反密码子碱基。通过在tRNA溶液中一点一点地加入同源氨基酸，通过检查饱和效应来检测这些tRNAs与同源氨基酸的特异性相互作用。测得亲和系数为100&lt；M^(-1)&gt；，相当大。另一方面，西德的Poerschke未能找到符合C4N理论的~lt；tRNA^(Phe)&gt；的特异性。将精确的紫外吸收光谱应用于类反密码子二核苷一磷酸的研究，发现它们与氨基酸及其酰胺和甲酯的特异性相互作用。只有在中性氨基酸的情况下才能发现完全特异性。上述实验似乎表明，遗传密码只不过是核酸碱基和氨基酸之间的特定相互作用表。

It is shown by molecular building and by semi-empirical calculations that complex of four nucleotides (C4N) composed of three anticodon bases and a discriminator base on a tRNA has a pocket on it to accept the cognate amino acid. This relationship could be the molecular basis of the genetic code. We have attempted to detect the specific interaction between tRNA (or oligonucleotide) and amino acid by using three spectroscopic methods such as ultraviolet absorption, fluorescence, and circular dichroism: In the C4N model, it can be predicted that <tRNA^(Asp)> and <tRNA^(Glu)> can discriminate their cognate amino acids without the discriminator base, while <tRNA^(Phe)> not. <tRNA^(Asp)> and <tRNA^(Glu)> have queosine and m n <m^5> <S^2> U as their first anticodon bases, respectively. By adding the cognate amino acid little by little to the tRNA solutions, the specific interaction of these tRNAs with the cognate amino acids has been detected by checking the saturation effect. The affinity coefficient were measured to be of the order of 100 <M^(-1)> , fairly large. On the other hand, Poerschke of West Germany could not find the specificity for <tRNA^(Phe)> , in accord with C4N theory. The precise ultraviolet absorbance spectroscopy was applied to the cases of anticodon-like dinucleoside monophosphates to find the specific interaction with the amino acids, their amides, and their methyl esters. The complet specificity was found only in the case of neutral amino acids. The above experiments appears to suggest that the genetic code is nothing but the specific interaction table between the nucleic acid bases and the amino acid.