Duggleby R G, Christopherson R I
Eur J Biochem. 1984 Aug 15;143(1):221-6. doi: 10.1111/j.1432-1033.1984.tb08362.x.
When a tight-binding inhibitor interacts with a target enzyme of a metabolic pathway, the end products of the pathway are depleted and the substrate(s) for the inhibited reaction accumulate. The accumulating substrate(s) can reach a concentration which is sufficiently high that the inhibition is effectively reversed, with restoration of the original flux through the inhibited reaction. We have recently developed a theoretical model for this phenomenon which we have called 'metabolic resistance' [R. I. Christopherson and R. G. Duggleby (1983) Eur. J. Biochem. 134, 331-335]. In the present communication, we have successfully used the technique of numerical integration to simulate the effects of inhibition of several enzymes in the pathway of pyrimidine biosynthesis. Utilizing appropriate dissociation constants and enzyme concentrations for the inhibited systems, these simulations are consistent with published experimental data for the interactions of N-phosphonacetyl-L-aspartate (P AcAsp) with mammalian aspartate transcarbamoylase in vitro [R. I. Christopherson and M. E. Jones (1980) J. Biol. Chem. 255, 11 381 -11 395] and of 5-fluorodeoxyuridine 5'-phosphate (FdUMP) with thymidylate synthetase in vivo [R. G. Moran, C. P. Spears, and C. Heidelberger (1979) Proc. Natl Acad. Sci. USA 76, 1456- 1460]. In addition we present a simulation of the expected effect in vivo of phosphoribofuranosyl barbituric acid (BMP), a tight-binding inhibitor of OMP decarboxylase [H. L. Levine, R. S. Brody, and F. H. Westheimer (1980) Biochemistry 19, 4993- 4999]. This simulation shows that on addition of BMP, there is a sequential depletion of all pyrimidine intermediates between UMP and dCDP and a concomitant accumulation of OMP. Eventually, OMP reaches a new steady-state concentration and the concentrations of the depleted intermediates rise to their original levels. We have simulated the depletion of dCDP at various concentrations of BMP; since dCDP is comitted to DNA synthesis we can integrate the dCDP concentrations over time to calculate the amount of DNA synthesis and thereby predict the delay in cell division which would be elicited by BMP. This form of analysis may help to explain in quantitative terms why inhibitors of nucleic acid biosynthesis have a selective toxicity for rapidly growing tumour cells.
当一种紧密结合抑制剂与代谢途径的靶酶相互作用时，该途径的终产物会耗尽，被抑制反应的底物会积累。积累的底物浓度可能会足够高，从而有效地逆转抑制作用，使被抑制反应恢复原来的通量。我们最近针对这种现象开发了一个理论模型，称之为“代谢抗性”[R. I. 克里斯托弗森和R. G. 达格利比（1983年），《欧洲生物化学杂志》134卷，331 - 335页]。在本通讯中，我们成功地运用数值积分技术模拟了嘧啶生物合成途径中几种酶被抑制的效应。利用被抑制系统合适的解离常数和酶浓度，这些模拟结果与已发表的关于N - 膦酰乙酰 - L - 天冬氨酸（P AcAsp）与哺乳动物天冬氨酸转氨甲酰酶在体外相互作用的实验数据[R. I. 克里斯托弗森和M. E. 琼斯（1980年），《生物化学杂志》255卷，11381 - 11395页]以及5 - 氟脱氧尿苷5'-磷酸（FdUMP）与胸苷酸合成酶在体内相互作用的实验数据[R. G. 莫兰、C. P. 斯皮尔斯和C. 海德伯格（1979年），《美国国家科学院院刊》76卷，1456 - 1460页]一致。此外，我们还模拟了磷酸核糖呋喃基巴比妥酸（BMP），一种OMP脱羧酶的紧密结合抑制剂，在体内的预期效应[H. L. 莱文、R. S. 布罗迪和F. H. 韦斯特海默（1980年），《生物化学》19卷，4993 - 4999页]。该模拟结果表明，加入BMP后，UMP和dCDP之间所有嘧啶中间体都会依次耗尽，同时OMP会积累。最终，OMP达到新的稳态浓度，耗尽的中间体浓度会回升到原来的水平。我们模拟了不同浓度BMP下dCDP的耗尽情况；由于dCDP参与DNA合成，我们可以对dCDP浓度随时间进行积分，以计算DNA合成量，从而预测BMP引发的细胞分裂延迟。这种分析形式可能有助于从定量角度解释为什么核酸生物合成抑制剂对快速生长的肿瘤细胞具有选择性毒性。
