Kleber H P
Acta Biol Med Ger. 1975;34(5):723-32.
Acinetobacter calcoaceticus contains two forms of NADP+-dependent isocitrate dehydrogenases differing, among others, by their molecular weights and regulatory properties. The regulation of the high-molecular form of isocitrate dehydrogenase and of isocitrate lyase by organic acids, either belonging or related to the citrate and glyoxalate cycle, is investigated. While alpha-ketoglutarate and oxalacetate competitively inhibit the isocitrate dehydrogenase against Ds-isocitrate, glyoxylate and pyruvate were found to increase Vmax and to lower the KM value for Ds-isocitrate and NADP+. Simultaneous addition of oxalacetate and glyoxylate (not, however, addition of the nonenzymatically formed condensation product of both compound) nullified the activation of isocitrate dehydrogenase by glyoxylate, and potentiates the inhibitory effect of oxalacetate. Alpha-ketoglutarate, succinate, and phosphoenolpyruvate inhibit the isocitrate lyase in a noncompetitive fashion against DS-isocitrate; L-malate, oxalacetate and glyoxylate inhibit competitively. The intermediates of the citrate and glyoxylate cycle afford additive inhibition of the isocitrate lyase. The importance of organic acids of the citrate and glyoxylate cycle and of phosphoenolpyruvate for the regulation of the citrate and glyoxylate cycle at the level of isocitrate dehydrogenase and isocitrate lyase is discussed.
醋酸钙不动杆菌含有两种依赖NADP⁺的异柠檬酸脱氢酶，它们的分子量和调节特性等有所不同。本文研究了柠檬酸和乙醛酸循环中的有机酸对高分子形式的异柠檬酸脱氢酶和异柠檬酸裂解酶的调节作用。虽然α-酮戊二酸和草酰乙酸能竞争性抑制异柠檬酸脱氢酶对Ds-异柠檬酸的作用，但乙醛酸和丙酮酸却能提高Vmax，并降低对Ds-异柠檬酸和NADP⁺的KM值。同时添加草酰乙酸和乙醛酸（然而，不是添加两种化合物非酶促形成的缩合产物）会消除乙醛酸对异柠檬酸脱氢酶的激活作用，并增强草酰乙酸的抑制作用。α-酮戊二酸、琥珀酸和磷酸烯醇丙酮酸以非竞争性方式抑制异柠檬酸裂解酶对DS-异柠檬酸的作用；L-苹果酸、草酰乙酸和乙醛酸则竞争性抑制。柠檬酸和乙醛酸循环的中间产物对异柠檬酸裂解酶有累加抑制作用。本文讨论了柠檬酸和乙醛酸循环中的有机酸以及磷酸烯醇丙酮酸在异柠檬酸脱氢酶和异柠檬酸裂解酶水平上对柠檬酸和乙醛酸循环调节的重要性。
