Holme E
Biochemistry. 1975 Nov 4;14(22):4999-5003. doi: 10.1021/bi00693a033.
The steady-state kinetics of thymine 7-hydroxylase (thymine, 2-oxoglutarate dioxygenase, EC 1.14.11.6) has been investigated. Initial velocity plots were all found to be linear and intersecting. Variation in concentration of two of the substrates, when the third substrate was at a constant high or low concentration, gave initial velocity plots that conform to an ordered sequential mechanism, where thymine is the second substrate to add. With 5-carboxyuracil, which is the end product in the sequential oxygenation of thymine, a competitive inhibition pattern was observed when 2-ketoglutarate was the variable substrate. When either thymine or oxygen was the variable substrate a noncompetitive inhibition pattern was obtained. When either 2-ketoglutarate or thymine was the variable substrate the inhibition patterns observed with bicarbonate were noncompetitive. With succinate noncompetitive inhibition patterns with hyperbolic intercept replots were obtained. These results are consistent with an ordered sequential kinetic mechanism, where 2-ketoglutarate is added first, followed by thymine and oxygen, and the products are released in the order: bicarbonate, succinate, and 5-hydroxymethyluracil. The order of the two last mentioned products, however, is changed in the presence of succinate.
对胸腺嘧啶7-羟化酶（胸腺嘧啶，2-酮戊二酸双加氧酶，EC 1.14.11.6）的稳态动力学进行了研究。发现初始速度图均为线性且相交。当第三种底物处于恒定的高浓度或低浓度时，两种底物浓度的变化给出了符合有序序列机制的初始速度图，其中胸腺嘧啶是第二个添加的底物。对于5-羧基尿嘧啶，它是胸腺嘧啶顺序氧化的终产物，当2-酮戊二酸是可变底物时，观察到竞争性抑制模式。当胸腺嘧啶或氧气是可变底物时，获得非竞争性抑制模式。当2-酮戊二酸或胸腺嘧啶是可变底物时，观察到的碳酸氢盐抑制模式是非竞争性的。对于琥珀酸，获得了具有双曲线截距重绘的非竞争性抑制模式。这些结果与有序序列动力学机制一致，其中首先添加2-酮戊二酸，然后是胸腺嘧啶和氧气，产物按以下顺序释放：碳酸氢盐、琥珀酸和5-羟甲基尿嘧啶。然而，在琥珀酸存在的情况下，最后提到的两种产物的顺序会发生变化。
