MECHANISM OF INHIBITORY EFFECT OF GLYOXYLATE PLUS OXALOACETATE AND OXALOMALATE ON NADP-SPECIFIC ISOCITRATE DEHYDROGENASE
MECHANISM OF INHIBITORY EFFECT OF GLYOXYLATE PLUS OXALOACETATE AND OXALOMALATE ON NADP-SPECIFIC ISOCITRATE DEHYDROGENASE
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DOI：
10.1016/0005-2744(76)90180-7
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发表时间：
1976-01-01
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影响因子：
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通讯作者：
INGEBRETSEN, OC
中科院分区：
文献类型：
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作者：
INGEBRETSEN, OC
用稳态方法以及停流技术研究了乙醛酸加草酰乙酸以及草酰苹果酸对猪心的NADP - 连接的异柠檬酸脱氢酶（苏 - Ds - 异柠檬酸：NADP⁺氧化还原酶（脱羧），EC 1.1.1.42）的影响。当乙醛酸和草酰乙酸的等摩尔混合物在加入测定混合物之前预混合不同时间时，抑制程度随预混合时间增加。乙醛酸加草酰乙酸的抑制是由这两种成分之间可逆相互作用形成的一种化合物引起的。乙醛酸加草酰乙酸以及草酰苹果酸至少以3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。如果酶与NADP加金属离子预混合，在用异柠檬酸引发反应后，在反应速率达到恒定值之前会出现时间滞后。抑制剂增强了NADP加金属离子对酶的这种作用。先前已表明该酶可被金属络合剂激活。在某些测定条件下，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引起酶的初始激活。关于上述抑制剂对酶作用机制的争议可能是由于它们以几种不同方式影响酶这一事实。
The effects of glyoxylate plus oxaloacetate and of oxalomalate on the NADP-linked isocitrate dehydrogenase (threo-DS-isocitrate:NADP+ oxidoreductas (decarboxylating), EC 1.1.1.42) from pig heart were 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 inhibition by glyoxylate plus oxaloacetate is caused by a compound formed in a reversible interaction between the 2 components. Glyoxylate plus oxaloacetate and oxalomalate affected the enzyme in at least 3 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. 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 enhanced this effect of NADP plus metal ions on the enzyme. It was previously 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 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.