Salter M, Knowles R G, Pogson C I
Biochem J. 1986 Mar 15;234(3):635-47. doi: 10.1042/bj2340635.
The quantitative importance of the individual steps of aromatic amino acid metabolism in rat liver was determined by calculation of the respective Control Coefficients (Strengths). The Control Coefficient of tryptophan 2,3-dioxygenase for tryptophan degradation was determined in a variety of physiological conditions and with a range of activities of tryptophan 2,3-dioxygenase. The Control Coefficient varied from 0.75 with basal enzyme activity to 0.25 after maximal induction of the enzyme by dexamethasone. The remainder of the control for tryptophan degradation was associated with the transport of the amino acid across the plasma membrane, with only very small contributions from kynureninase and kynurenine hydroxylase. The Control Coefficients of tyrosine aminotransferase for tyrosine degradation were approx. 0.70 and 0.20 with basal and dexamethasone-induced tyrosine aminotransferase activities respectively; the Control Coefficients of the transport of the amino acid into the cell were 0.22 and 0.58 respectively. Phenylalanine hydroxylase was found to have a Control Coefficient for the degradation of phenylalanine of approx. 0.50 under conditions of basal enzyme activity; after maximal activation by glucagon, the Control Coefficient decreased to 0.12. The transport of phenylalanine was responsible for the remaining control in the pathway. These results have important implications, directly for the regulation of aromatic amino acid metabolism in the liver, and indirectly for the regulation of neuroamine synthesis in the brain.
通过计算各自的控制系数（强度），确定了大鼠肝脏中芳香族氨基酸代谢各个步骤的定量重要性。在多种生理条件下以及色氨酸2,3-双加氧酶的一系列活性水平下，测定了色氨酸2,3-双加氧酶对色氨酸降解的控制系数。该控制系数在基础酶活性时为0.75，在用地塞米松最大程度诱导该酶后降至0.25。色氨酸降解的其余控制与氨基酸跨质膜的转运有关，犬尿氨酸酶和犬尿氨酸羟化酶的贡献非常小。酪氨酸转氨酶对酪氨酸降解的控制系数在基础和地塞米松诱导的酪氨酸转氨酶活性下分别约为0.70和0.20；氨基酸进入细胞的转运控制系数分别为0.22和0.58。发现在基础酶活性条件下苯丙氨酸羟化酶对苯丙氨酸降解的控制系数约为0.50；在胰高血糖素最大程度激活后，控制系数降至0.12。苯丙氨酸的转运负责该途径中的其余控制。这些结果具有重要意义，直接关乎肝脏中芳香族氨基酸代谢的调节，间接关乎大脑中神经胺合成的调节。
