Raunio R P, Lindberg R K, Jenkins W T
Arch Biochem Biophys. 1984 Aug 15;233(1):43-9. doi: 10.1016/0003-9861(84)90599-x.
The bimolecular association and first-order dissociation rate constants for the reactions of aminooxyacetate and hydroxylamine with the cytosolic aspartate aminotransferase (EC 2.6.1.1) of pig heart were estimated from pH 4.8 to pH 9.5. The acidic form of the enzyme (pK = 6.3) was more reactive than the unprotonated enzyme, but the rates of breakdown of the complexes were not affected by pH. The equilibrium dissociation constants, which were of the order of magnitude of 10(-7) M, were thus lowest at acidic pH values. Aminooxyacetate and hydroxylamine reacted similarly, with the former being more reactive. Glutarate and acetate inhibited the rates of formation and dissociation but had no effect on the overall equilibrium constants between enzyme and inhibitor. On the other hand, the substrate analog erythro-beta-hydroxy-L-aspartate, which forms a complex with the enzyme prosthetic group, acted competitively by preventing the inhibitors from reacting. The rate constants for formation of complexes with free pyridoxal phosphate were much less than those for the enzyme and, unlike the enzyme, hydroxylamine was more reactive than aminooxyacetate.
在pH值4.8至9.5范围内，估算了氨基氧基乙酸和羟胺与猪心胞质天冬氨酸转氨酶（EC 2.6.1.1）反应的双分子缔合速率常数和一级解离速率常数。酶的酸性形式（pK = 6.3）比未质子化的酶更具反应活性，但复合物的分解速率不受pH值影响。因此，平衡解离常数在酸性pH值下最低，其数量级为10(-7) M。氨基氧基乙酸和羟胺的反应方式相似，前者反应活性更高。戊二酸和乙酸抑制了形成和解离速率，但对酶与抑制剂之间的整体平衡常数没有影响。另一方面，与酶辅基形成复合物的底物类似物赤藓糖-β-羟基-L-天冬氨酸通过阻止抑制剂反应而表现出竞争性作用。与游离磷酸吡哆醛形成复合物的速率常数远低于与酶形成复合物的速率常数，并且与酶不同，羟胺比氨基氧基乙酸更具反应活性。
