Hove-Jensen B, Nygaard P
Eur J Biochem. 1982 Aug;126(2):327-32. doi: 10.1111/j.1432-1033.1982.tb06782.x.
From an Escherichia coli purine auxotroph a mutant defective in phosphoribosylpyrophosphate (PRib-PP) synthetase has been isolated and partially characterized. In contrast to the parental strain, the mutant was able to grow on nucleosides as purine source, whereas growth on purine bases was reduced. Kinetic analysis of the mutant PRib-PP synthetase revealed an apparent Km for ATP and ribose 5-phosphate of 1.0 mM and 240 muM respectively, compared to 60 muM and 45 muM respectively for the wild-type enzyme. ADP, which inhibits the wild-type enzyme at a concentration of 0.5 mM ribose 5-phosphate, stimulated the mutant enzyme. The activity of PRib-PP synthetase in crude extract was higher in the mutant than in the parent. When starved for purines an accumulation of PRib-PP was observed in the parent strain, while the pool decreased in the mutant. During pyrimidine starvation derepression of PRib-PP synthetase activity was observed in both strains, although to a lesser extent in the mutant. Our data suggest that the mutant harbors a mutation in the structural gene for PRib-PP synthetase. The mutation responsible for the altered PRib-PP synthetase was located in the purB-hemA region at 26 min on the recalibrated linkage map.
从一株大肠杆菌嘌呤营养缺陷型菌株中分离出了一株磷酸核糖焦磷酸（PRib-PP）合成酶缺陷的突变体，并对其进行了部分特性分析。与亲本菌株相比，该突变体能够以核苷作为嘌呤源生长，而以嘌呤碱为碳源时生长受到抑制。对突变体PRib-PP合成酶的动力学分析表明，其对ATP和5-磷酸核糖的表观Km值分别为1.0 mM和240 μM，而野生型酶的这两个值分别为60 μM和45 μM。在5-磷酸核糖浓度为0.5 mM时抑制野生型酶的ADP却能刺激突变体酶。粗提物中PRib-PP合成酶的活性在突变体中比在亲本中更高。当嘌呤饥饿时，在亲本菌株中观察到PRib-PP的积累，而在突变体中该库减少。在嘧啶饥饿期间，在两种菌株中均观察到PRib-PP合成酶活性的去阻遏，尽管在突变体中程度较小。我们的数据表明，该突变体在PRib-PP合成酶的结构基因中存在突变。导致PRib-PP合成酶改变的突变位于重新校准的连锁图谱上26分钟处的purB-hemA区域。
