Henderson J F, Lowe J K, Barankiewicz J
Ciba Found Symp. 1977(48):3-21. doi: 10.1002/9780470720301.ch2.
The conceptual framework which underlies many studies of purine and pyrimidine metabolism in intact cells has been critically evaluated. The model that is implicit in many such studies is the single, partially purified enzyme. This paper gives examples both of instances in which the extrapolation of results of enzymes studies to intact cells has been successful and of instances in which enzymes behave differently in the intact cell than in cell extracts. Pitfalls in the extrapolation of results of enzyme studies to intact cells concern (a) metabolic pathways, (b) intracellular enzyme activities, (c) enzyme regulation, and (d) intracellular metabolite concentrations. Examples are also given of situations in which perturbations in one aspect of purine or pyrimidine metabolism lead to changes in other aspects, often distant in the network of reactions.
许多关于完整细胞中嘌呤和嘧啶代谢的研究背后的概念框架已得到严格评估。许多此类研究中隐含的模型是单一的、部分纯化的酶。本文给出了一些例子，既有酶学研究结果成功外推至完整细胞的情况，也有酶在完整细胞中的行为与在细胞提取物中不同的情况。将酶学研究结果外推至完整细胞时存在的陷阱涉及：（a）代谢途径；（b）细胞内酶活性；（c）酶调节；以及（d）细胞内代谢物浓度。还给出了一些情况的例子，其中嘌呤或嘧啶代谢某一方面的扰动会导致其他方面的变化，这些变化在反应网络中往往相距甚远。
