Zeng An-Ping, Modak Jayant, Deckwer Wolf-Dieter
GBF-Gesellschaft für Biotechnologische Forschung mbH, Biochemical Engineering Division, Mascheroder Weg 1, 38124 Braunschweig, Germany.
Biotechnol Prog. 2002 Nov-Dec;18(6):1265-76. doi: 10.1021/bp020097o.
Pyruvate conversion to acetyl-CoA by the pyruvate dehydrogenase (PDH) multienzyme complex is known as a key node in affecting the metabolic fluxes of animal cell culture. However, its possible role in causing possible nonlinear dynamic behavior such as oscillations and multiplicity of animal cells has received little attention. In this work, the kinetic and dynamic behavior of PDH of eucaryotic cells has been analyzed by using both in vitro and simplified in vivo models. With the in vitro model the overall reaction rate (nu(1)) of PDH is shown to be a nonlinear function of pyruvate concentration, leading to oscillations under certain conditions. All enzyme components affect nu(1) and the nonlinearity of PDH significantly, the protein X and the core enzyme dihydrolipoamide acyltransferase (E2) being mostly predominant. By considering the synthesis rates of pyruvate and PDH components the in vitro model is expanded to emulate in vivo conditions. Analysis using the in vivo model reveals another interesting kinetic feature of the PDH system, namely, multiple steady states. Depending on the pyruvate and enzyme levels or the operation mode, either a steady state with high pyruvate decarboxylation rate or a steady state with significantly lower decarboxylation rate can be achieved under otherwise identical conditions. In general, the more efficient steady state is associated with a lower pyruvate concentration. A possible time delay in the substrate supply and enzyme synthesis can also affect the steady state to be achieved and leads to oscillations under certain conditions. Overall, the predictions of multiplicity for the PDH system agree qualitatively well with recent experimental observations in animal cell cultures. The model analysis gives some hints for improving pyruvate metabolism in animal cell culture.
丙酮酸脱氢酶（PDH）多酶复合体将丙酮酸转化为乙酰辅酶A是影响动物细胞培养代谢通量的关键节点。然而，其在导致动物细胞可能出现的非线性动态行为（如振荡和多重性）方面的潜在作用却很少受到关注。在这项工作中，通过使用体外模型和简化的体内模型分析了真核细胞PDH的动力学和动态行为。在体外模型中，PDH的总反应速率（ν(1)）显示为丙酮酸浓度的非线性函数，在某些条件下会导致振荡。所有酶组分均对ν(1)和PDH的非线性有显著影响，其中蛋白质X和核心酶二氢硫辛酰胺酰基转移酶（E2）的影响最为突出。通过考虑丙酮酸和PDH组分的合成速率，将体外模型扩展以模拟体内条件。使用体内模型进行的分析揭示了PDH系统另一个有趣的动力学特征，即多重稳态。根据丙酮酸和酶的水平或操作模式，在其他条件相同的情况下，可以实现高丙酮酸脱羧速率的稳态或脱羧速率显著较低的稳态。一般来说，效率更高的稳态与较低的丙酮酸浓度相关。底物供应和酶合成中可能存在的时间延迟也会影响所达到的稳态，并在某些条件下导致振荡。总体而言，PDH系统多重性的预测与动物细胞培养中最近的实验观察结果在定性上吻合良好。模型分析为改善动物细胞培养中的丙酮酸代谢提供了一些线索。
