Ingebretsen O C
Biochim Biophys Acta. 1976 Dec 8;452(2):302-9. doi: 10.1016/0005-2744(76)90180-7.
The effects of glyoxylate plus oxaloacetate and of oxalomalate on the NADP-linked isocitrate dehydrogenase (threo-DS-isocitrate:NADP+ oxidoreductase (decarboxylating, EC 1.1.1.42) from pig heart from been studied with steady state methods as well as with stopped flow technique. When equimolar mixtures of glyoxylate and oxaloacetate were premixed for different lengths of time prior to addition to the assay mixture, the extent of inhibition increased with the premixing time. The results indicated that the inhibition by glyoxylate plus oxaloacetate is caused by a compound formed in a reversible interaction between the two components. Glyoxylate plus oxaloacetate and oxalomalate affected the enzyme in at least three different ways. They inhibited the enzyme in a reaction competitive with regard to the substrate isocitrate. This inhibition needed a certain time to be fully expressed. The time lag could be eliminated by premixing of the enzyme and inhibitor with NADP plus metal ion. Secondly, if the enzyme is premixed with NADP plus metal ions, a time lag occurs before the reaction rate approaches a constant value after initiation of the reaction with isocitrate. The inhibitors were found to enhance this effect of NADP plus metal ions on the enzyme. Thirdly, it has previously been shown that the enzyme can be activated by metal complexing agents. Glyoxylate plus oxaloacetate as well as oxalomalate are able to form complexes with metal ions and were found to cause an initial activation of the enzyme under certain assay conditions. The controversy regarding the mechanism of action of the above inhibitors on the enzyme is probably due to the fact that they affect the enzyme in several different ways.
已采用稳态方法以及停流技术研究了乙醛酸加草酰乙酸和草酰苹果酸对猪心中与NADP相关的异柠檬酸脱氢酶（苏式-DS-异柠檬酸：NADP +氧化还原酶（脱羧，EC 1.1.1.42））的影响。当在加入测定混合物之前将等摩尔的乙醛酸和草酰乙酸混合物预混合不同的时间长度时，抑制程度随预混合时间增加。结果表明，乙醛酸加草酰乙酸的抑制作用是由两种成分之间可逆相互作用形成的一种化合物引起的。乙醛酸加草酰乙酸和草酰苹果酸至少以三种不同方式影响该酶。它们在与底物异柠檬酸竞争的反应中抑制该酶。这种抑制需要一定时间才能充分表现出来。通过将酶和抑制剂与NADP加金属离子预混合可以消除时间滞后。其次，如果将酶与NADP加金属离子预混合，则在用异柠檬酸启动反应后，反应速率在接近恒定值之前会出现时间滞后。发现抑制剂会增强NADP加金属离子对该酶的这种作用。第三，先前已表明该酶可被金属络合剂激活。乙醛酸加草酰乙酸以及草酰苹果酸能够与金属离子形成络合物，并且发现在某些测定条件下会引起该酶的初始激活。关于上述抑制剂对该酶作用机制的争议可能是由于它们以几种不同方式影响该酶这一事实。
