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Investigation of homochiral origin on the basis of comparison between enzymatic activity and active site for both enantiomers

在比较两种对映体的酶活性和活性位点的基础上研究纯手性起源

基本信息

批准号：
10680560
负责人：
SHIMADA Akihiko
金额：
$ 2.11万
依托单位：
University of Tsukuba
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 1999
项目状态：
已结题

项目摘要

Experiments were performed to identify the relative position of an active site for D-tryptophan with that for L-tryptophan, and the following results were obtained.1. D-tryptophan was not racemized at all in highly concentrated diammoniumhydrogen phosphate solution.2. The inhibition types of potassium pyruvate and indolepyruvate were analyzed for L-tryptohan degradation reaction. The former was competitive, but the latter switched from competitive to noncompetitive type with increasing diammoniumhydrogen phosphate concentrations.3. γ-tryptophanase, which was inactivated to D-tryptophan due to γ-ray irradiation, inhibited competitively even in the presence of diammoniumhydrogen phosphate.4. On the basis of the above results, positional relationship between an active site for D-tryptophan and one for L-tryptophan could be illustrated as follows. That is, heterocyclic moiety of D-tryptophan binds with another binding site remote from a binding site for L-tryptophan. The location of D-tryptophan has an appropriate angle to react with tryptophanase. Thus, D-tryptophan can become to tryptophanase.5. Although the stereoselectivity of enzyme has been ever considered to be permanently strict, it was shown by this study that environmental change around the enzyme made it ambiguous.6. We will investigate how a structural change effective to chirally stereoselective change is.

通过实验确定了D-色氨酸和L-色氨酸活性位点的相对位置，得到了以下结果. D-色氨酸在高浓度磷酸氢二铵溶液中完全不发生外消旋.分析了丙酮酸钾和吲哚丙酮酸钾对L-色氨酸降解反应的抑制类型。前者为竞争型，而后者随磷酸氢二铵浓度的增加由竞争型向非竞争型转变.γ-色氨酸酶在γ射线照射下被D-色氨酸灭活，即使在磷酸氢二铵存在下也受到竞争性抑制.基于上述结果，D-色氨酸的活性位点和L-色氨酸的活性位点之间的位置关系可以如下所示。也就是说，D-色氨酸的杂环部分与远离L-色氨酸的结合位点的另一个结合位点结合。D-色氨酸的位置有一个合适的角度与色氨酸酶反应。因此，D-色氨酸可以转化为色氨酸酶.虽然酶的立体选择性一直被认为是严格的，但本研究表明，酶周围环境的变化使其具有模糊性。我们将研究如何有效的手性立体选择性变化的结构变化。