Modak Jayant, Deckwer Wolf-Dieter, Zeng An-Ping
GBF-Gesellschaft für Biotechnologische Forschung mbH, Biochemical Engineering Division, Mascheroder Weg 1, 38124 Braunschweig, Germany.
Biotechnol Prog. 2002 Nov-Dec;18(6):1157-69. doi: 10.1021/bp025613p.
Metabolic control analysis (MCA) of pyruvate dehydrogenase multienzyme (PDH) complex of eucaryotic cells has been carried out using both in vitro and in vivo mechanistic models. Flux control coefficients (FCC) for the sensitivity of pyruvate decarboxylation rate to activities of various PDH complex reactions are determined. FCCs are shown to be strong functions of both pyruvate levels and various components of PDH complex. With the in vitro model, FCCs are shown to be sensitive to only the E1 component of the PDH complex at low pyruvate concentrations. At high pyruvate concentrations, the control is shared by all of the components, with E1 having a negative influence while the other three components, E2, X, and K, exert a positive control over the pyruvate decarboxylation rate. An unusual behavior of deactivation of the E1 component leading to higher net PDH activity is shown to be linked to the combined effect of protein X acylation and E1 deactivation. The steady-state analysis of the in vivo model reveals multiple steady state behavior of pyruvate metabolism with two stable and one unstable steady-states branches. FCCs also display multiplicity, showing completely different control distribution exerted by pyruvate and PDH components on three branches. At low pyruvate concentrations, pyruvate supply dominates the decarboxylation rate and PDH components do not exert any significant control. Reverse control distribution is observed at high pyruvate concentration. The effect of dilution due to cell growth on pyruvate metabolism is investigated in detail. While pyruvate dilution effects are shown to be negligible under all conditions, significant PDH complex dilution effects are observed under certain conditions. Comparison of in vitro and in vivo models shows that PDH components exert different degrees of control outside and inside the cells. At high pyruvate levels, PDH components are shown to exert a higher degree of control when reactions are taking place inside the cells as compared to the in vitro situation.
已使用体外和体内机制模型对真核细胞的丙酮酸脱氢酶多酶（PDH）复合物进行了代谢控制分析。确定了丙酮酸脱羧速率对各种PDH复合物反应活性敏感性的通量控制系数（FCC）。结果表明，FCC是丙酮酸水平和PDH复合物各种组分的强函数。在体外模型中，在低丙酮酸浓度下，FCC仅对PDH复合物的E1组分敏感。在高丙酮酸浓度下，所有组分共同参与控制，E1具有负面影响，而其他三个组分E2、X和K对丙酮酸脱羧速率发挥正控制作用。E1组分失活导致净PDH活性升高的异常行为被证明与蛋白X酰化和E1失活的联合作用有关。体内模型的稳态分析揭示了丙酮酸代谢的多重稳态行为，有两个稳定和一个不稳定的稳态分支。FCC也表现出多重性，显示丙酮酸和PDH组分在三个分支上施加完全不同的控制分布。在低丙酮酸浓度下，丙酮酸供应主导脱羧速率，PDH组分不发挥任何显著控制作用。在高丙酮酸浓度下观察到相反的控制分布。详细研究了细胞生长引起的稀释对丙酮酸代谢的影响。虽然丙酮酸稀释效应在所有条件下都可忽略不计，但在某些条件下观察到显著的PDH复合物稀释效应。体外和体内模型的比较表明，PDH组分在细胞内外发挥不同程度的控制作用。在高丙酮酸水平下，与体外情况相比，当反应在细胞内发生时，PDH组分显示出更高程度的控制作用。
