Powers S G, Meister A
J Biol Chem. 1978 Feb 10;253(3):800-3.
Application of the pulse-chase procedure to study of the binding and utilization of ATP by glutamine-dependent carbamyl phosphate synthetase from Escherichia coli showed that the enzyme binds the two molecules of ATP used in this reaction at the same time, and that the two ATP-binding sites are functionally different. Thus, ATP bound to the first ATP site is used for carboxy phosphate formation, and ATP bound to the second ATP site is used for phosphorylation of carbamate. The present and previous findings support a mechanism that involves intermediate formation of two highly unstable intermediates: carboxy phosphate and carbamate. It is proposed that the presence of all of the reactants on the enzyme at the start of the catalytic cycle allows immediate utilization of these labile compounds in the carbamyl phosphate synthesis reaction.
采用脉冲追踪法研究大肠杆菌谷氨酰胺依赖性氨甲酰磷酸合成酶对ATP的结合和利用，结果表明该酶同时结合此反应中所利用的两分子ATP，且两个ATP结合位点在功能上有所不同。因此，结合于第一个ATP位点的ATP用于形成羧基磷酸，而结合于第二个ATP位点的ATP用于氨基甲酸盐的磷酸化。目前及先前的研究结果支持一种涉及两种高度不稳定中间体（羧基磷酸和氨基甲酸盐）中间形成的机制。有人提出，在催化循环开始时酶上存在所有反应物，使得这些不稳定化合物能在氨甲酰磷酸合成反应中立即被利用。
