Mosteller R D, Nishimoto K R, Bush P R, Golstein R V
J Biol Chem. 1982 Sep 10;257(17):10184-90.
The bifunctional tryptophan biosynthetic enzyme N-(5'-phosphoribosyl)anthranilate (PRA) isomerase/indole-3-glycerol phosphate (InGP) synthetase was purified from Escherichia coli cultures incubated under several conditions, some of which result in inactivation of the enzyme (starvation for ammonium or sulfate, chloramphenicol inhibition). Recovery of enzyme activity during purification from cultures incubated under inactivating conditions suggested that activity was restored or that an inhibitor was removed. In these preparations, the enzymatic properties were altered slightly but not in a manner that could account for inactivation. Each preparation exhibited one major protein species (Mr approximately 50,000) when analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis but revealed several species during isoelectric focusing in the range of pH 5.5 to 6.0. Comparison of the distribution of species indicated that modification to the more acidic forms had occurred in growing and nongrowing cells but not during stationary phase, glucose starvation, or energy depletion. The results suggested that inactivation and modification had occurred in vivo by an energy-dependent process. Several metabolites tested did not inhibit the purified enzyme. Attempts to detect an inhibitor in crude cell extracts were also not successful.
双功能色氨酸生物合成酶N-(5'-磷酸核糖基)邻氨基苯甲酸（PRA）异构酶/吲哚-3-甘油磷酸（InGP）合成酶是从在几种条件下培养的大肠杆菌培养物中纯化得到的，其中一些条件会导致该酶失活（铵或硫酸盐饥饿、氯霉素抑制）。从在失活条件下培养的培养物中纯化过程中酶活性的恢复表明活性得以恢复或抑制剂被去除。在这些制剂中，酶的性质略有改变，但并非以能够解释失活的方式改变。通过十二烷基硫酸钠-聚丙烯酰胺凝胶电泳分析时，每种制剂都显示出一种主要蛋白质种类（分子量约为50,000），但在pH 5.5至6.0范围内的等电聚焦过程中显示出几种种类。种类分布的比较表明，在生长和非生长细胞中发生了向更酸性形式的修饰，但在稳定期、葡萄糖饥饿或能量耗尽期间未发生。结果表明，失活和修饰是通过能量依赖过程在体内发生的。测试的几种代谢物均未抑制纯化的酶。在粗细胞提取物中检测抑制剂的尝试也未成功。
