来自牛心脏的NAD特异性异柠檬酸脱氢酶。与Ca2+螯合剂的相互作用。
NAD-specific isocitrate dehydrogenase from bovine heart. Interaction with Ca2+ chelators.
作者信息
Gabriel J L, Plaut G W
出版信息
Biochem J. 1985 Aug 1;229(3):817-22. doi: 10.1042/bj2290817.
The activity of NAD-specific isocitrate dehydrogenase was inhibited by EDTA, EGTA and other nitrogen-containing polycarboxylate Ca2+ chelators in the absence and in the presence of ADP by a mechanism that could not be attributed solely to the removal of free Ca2+. Carboxymethyltartronate (2-oxapropane-1,1,3-tricarboxylate), an oxygen ether polycarboxylate chelator, did not inhibit when ADP was absent. The activation by ADP, a positive effector of the enzyme, decreased with increasing concentration of carboxymethyltartronate, paralleling the removal of free Ca2+ by this chelator. The following were found when free Ca2+ was decreased to negligible concentrations (5-50 nM) with carboxymethyltartronate. (1) Free Ca2+ enhanced, but was not absolutely required for, activation by ADP. (2) Activation of enzyme activity by magnesium citrate neither required nor was increased by Ca2+ when ADP was absent. However, the potentiation of citrate activation by ADP was facilitated by free Ca2+. (3) The reversal of NADPH inhibition of enzyme activity by ADP did not absolutely require Ca2+, but it was enhanced by free Ca2+. (4) The inhibition of enzyme activity by NADH was not reversed by ADP either with or without Ca2+.
在有无二磷酸腺苷（ADP）存在的情况下，NAD特异性异柠檬酸脱氢酶的活性均受到乙二胺四乙酸（EDTA）、乙二醇双四乙酸（EGTA）和其他含氮多羧酸钙离子螯合剂的抑制，其抑制机制不能仅仅归因于游离钙离子的去除。羧甲基酒石酸酯（2-氧杂丙烷-1,1,3-三羧酸）是一种氧醚多羧酸螯合剂，在无ADP时不产生抑制作用。作为该酶的正效应物，ADP的激活作用随着羧甲基酒石酸酯浓度的增加而降低，这与该螯合剂去除游离钙离子的情况平行。当用羧甲基酒石酸酯将游离钙离子浓度降低到可忽略不计的水平（5 - 50 nM）时，发现了以下情况。（1）游离钙离子增强了ADP的激活作用，但并非绝对必需。（2）在无ADP时，柠檬酸镁对酶活性的激活既不需要钙离子，也不会因钙离子而增强。然而，游离钙离子促进了ADP对柠檬酸激活作用的增强。（3）ADP对NADPH抑制酶活性的逆转并非绝对需要钙离子，但游离钙离子会增强这种逆转作用。（4）无论有无钙离子，ADP都不能逆转NADH对酶活性的抑制作用。
Zotero 插件