Daumy G O, Cohn M S, Phillips A T
J Bacteriol. 1974 Dec;120(3):1249-55. doi: 10.1128/jb.120.3.1249-1255.1974.
Seventeen mutants of Pseudomonas putida that were unable to grow on threonine as nitrogen source owing to a lack of threonine dehydratase were isolated, and all were found to be unable to synthesize active urocanase. Spontaneous revertants selected for urocanase production concomitantly regained threonine dehydratase. Mutants that were unable to utilize urocanate as carbon source were also isolated, and these were defective in urocanase formation but were normal in threonine dehydratase levels. Since alpha-ketobutyrate is the prosthetic group for urocanase, these results are consistent with the proposal that threonine dehydratase is necessary for urocanase prosthetic group biosynthesis. However, the lack of urocanase activity in threonine dehydratase-negative mutants was shown not to be the result of reduced levels of endogenous free alpha-ketobutyrate, nor to the participation of threonine dehydratase in the initiation of urocanase biosynthesis through the conversion of threonyl-tRNA(Thr) to alpha-ketobutyryl-tRNA(Thr). Other alternatives for the participation of threonine dehydratase in urocanase biosynthesis are discussed.
分离出17株恶臭假单胞菌突变体，由于缺乏苏氨酸脱水酶，它们无法以苏氨酸作为氮源生长，并且发现所有突变体均无法合成有活性的尿刊酸酶。为生产尿刊酸酶而选择的自发回复突变体同时恢复了苏氨酸脱水酶活性。还分离出了无法利用尿刊酸盐作为碳源的突变体，这些突变体在尿刊酸酶形成方面存在缺陷，但苏氨酸脱水酶水平正常。由于α-酮丁酸是尿刊酸酶的辅基，这些结果与以下提议一致，即苏氨酸脱水酶对于尿刊酸酶辅基生物合成是必需的。然而，苏氨酸脱水酶阴性突变体中尿刊酸酶活性的缺乏并非内源性游离α-酮丁酸水平降低的结果，也不是由于苏氨酸脱水酶通过将苏氨酰-tRNA（Thr）转化为α-酮丁酰-tRNA（Thr）参与尿刊酸酶生物合成起始的结果。讨论了苏氨酸脱水酶参与尿刊酸酶生物合成的其他可能性。
