Stucki Jörg W, Urbanczik Robert
Department of Pharmacology, University of Bern, Switzerland.
FEBS J. 2005 Dec;272(24):6244-53. doi: 10.1111/j.1742-4658.2005.05005.x.
A representative model of mitochondrial pyruvate metabolism was broken down into its extremal independent currents and compared with experimental data obtained from liver mitochondria incubated with pyruvate as a substrate but in the absence of added adenosine diphosphate. Assuming no regulation of enzymatic activities, the free-flow prediction for the output of the model shows large discrepancies with the experimental data. To study the objective of the incubated mitochondria, we calculate the conversion cone of the model, which describes the possible input/output behaviour of the network. We demonstrate the consistency of the experimental data with the model because all measured data are within this cone. Because they are close to the boundary of the cone, we deduce that pyruvate is converted very efficiently (93%) to produce the measured extramitochondrial metabolites. We find that the main function of the incubated mitochondria is the production of malate and citrate, supporting the anaplerotic pathways in the cytosol, notably gluconeogenesis and fatty acid synthesis. Finally, we show that the major flow through the enzymatic steps of the mitochondrial pyruvate metabolism can be reliably predicted based on the stoichiometric model plus the measured extramitochondrial products. A major advantage of this method is that neither kinetic simulations nor radioactive tracers are needed.
线粒体丙酮酸代谢的一个代表性模型被分解为其极端独立电流，并与从以丙酮酸为底物但未添加二磷酸腺苷的情况下孵育的肝线粒体获得的实验数据进行比较。假设酶活性没有调节，该模型输出的自由流预测与实验数据存在很大差异。为了研究孵育线粒体的目标，我们计算了模型的转换锥，它描述了网络可能的输入/输出行为。我们证明了实验数据与模型的一致性，因为所有测量数据都在这个锥内。由于它们接近锥的边界，我们推断丙酮酸被非常有效地（93%）转化以产生测量到的线粒体外代谢物。我们发现孵育线粒体的主要功能是产生苹果酸和柠檬酸，支持细胞质中的回补途径，特别是糖异生和脂肪酸合成。最后，我们表明基于化学计量模型加上测量到的线粒体外产物，可以可靠地预测线粒体丙酮酸代谢酶促步骤的主要流量。这种方法的一个主要优点是既不需要动力学模拟也不需要放射性示踪剂。
