Bryce C F, Williams D C, John R A, Fasella P
Biochem J. 1976 Mar 1;153(3):571-7. doi: 10.1042/bj1530571.
Cytoplasmic aspartate aminotransferase and malate dehydrogenase were purified from pig heart. Kinetic parameters were determined for the separate reaction catalysed by each enzyme and used to predict the course of the coupled reaction: (see article). Although a lag phase should have been easily seen, none was detected. The same coupled reaction was also carried out by using radioactive aspartate in the presence of unlabelled oxaloacetate. The reaction was quenched with HClO4 after 70 ms and the specific radioactivity of the malate produced in this system was found to be essentially the same as that of the original aspartate. These results show that oxaloacetate produced by the aspartate aminotransferase is converted into malate by malate dehydrogenase before it equilibrates with the pool of unlabelled oxaloacetate and are consistent with a proposal that the enzymes are associated in a complex. However, no physical evidence of the existence of a complex could be found. An alternative means of compartmentation of the intermediate as an unstable isomer is considered.
从猪心中纯化出细胞质天冬氨酸转氨酶和苹果酸脱氢酶。测定了每种酶催化的单独反应的动力学参数，并用于预测偶联反应的进程：（见文章）。尽管应该很容易观察到一个滞后阶段，但并未检测到。在未标记草酰乙酸存在的情况下，使用放射性天冬氨酸也进行了相同的偶联反应。70毫秒后用高氯酸淬灭反应，发现该系统中产生的苹果酸的比放射性与原始天冬氨酸的比放射性基本相同。这些结果表明，天冬氨酸转氨酶产生的草酰乙酸在与未标记的草酰乙酸池平衡之前就被苹果酸脱氢酶转化为苹果酸，这与酶以复合物形式存在的提议一致。然而，没有发现复合物存在的物理证据。考虑了将中间体作为不稳定异构体进行分隔的另一种方式。
