Hadar R, Slonim A, Kuhn J
J Bacteriol. 1976 Mar;125(3):1096-1104. doi: 10.1128/jb.125.3.1096-1104.1976.
Mutants of Escherichia coli K-12 that require L-tryptophan (trp) are normally unable to utilize D-tryptophan to fulfill their requirement. However, secondary mutations (dadR) that confer this ability can be isolated. In such strains two distinct enzymes are found to be produced at high levels: D-amino acid oxidase (EC 1.4.3.3) and D-tryptophan oxidase. A convenient assay procedure for D-tryptophan oxidase is described. The two enzymes could be distinguished on the basis of their sensitivity to inhibition by L-phenylalanine and L-tyrosine. Strains that were trp dadR could not grow with D-tryptophan in the presence of L-phenylalanine, but further mutations, Fyo, could be isolated that allowed growth under these conditions. Some of them were characterized by further increases in the level of D-tryptophan oxidase activity and a sharp decrease in D-amino acid oxidase. These kinds of Fyo mutations lay in or near the dadR gene. The substrate specificity of the two enzymes toward a large number of compounds was examined. The transamination of aromatic keto acids was investigated. In the wild-type strain only a single enzyme, transaminase A (EC 2.6.1.5), was found, and it was irreversibly activated when subjected to elevated temperatures. The present state of our knowledge on D-amino acid utilization in E. coli is summarized.
需要L - 色氨酸（trp）的大肠杆菌K - 12突变体通常无法利用D - 色氨酸来满足其需求。然而，可以分离出赋予这种能力的二次突变（dadR）。在这类菌株中，发现有两种不同的酶大量产生：D - 氨基酸氧化酶（EC 1.4.3.3）和D - 色氨酸氧化酶。本文描述了一种简便的D - 色氨酸氧化酶测定方法。这两种酶可根据它们对L - 苯丙氨酸和L - 酪氨酸抑制作用的敏感性来区分。trp dadR菌株在L - 苯丙氨酸存在下不能利用D - 色氨酸生长，但可以分离出进一步的突变体Fyo，使其在这些条件下能够生长。其中一些突变体的特征是D - 色氨酸氧化酶活性进一步增加，而D - 氨基酸氧化酶活性急剧下降。这类Fyo突变位于dadR基因内或其附近。研究了这两种酶对大量化合物的底物特异性。对芳香族酮酸的转氨作用进行了研究。在野生型菌株中只发现了一种酶，转氨酶A（EC 2.6.1.5），并且在高温下会被不可逆地激活。总结了我们目前对大肠杆菌中D - 氨基酸利用的认识状况。
