Lill U, Kollmann-Koch A, Bibinger A, Eggerer H
Institut für Physiologische Chemie, Technischen Universität München, Federal Republic of Germany.
Eur J Biochem. 1991 Jun 15;198(3):767-73. doi: 10.1111/j.1432-1033.1991.tb16079.x.
Substrate and intermediate analogue inhibitors of enzymes were prepared in which the thioester oxygen of acyl-CoA substrates is replaced by hydrogen with formation of CoA-thioethers. Experiments performed with ATP citrate lyase and S-(3,4-dicarboxy-3-hydroxybutyl)-CoA are consistent with citryl-CoA but not with citryl-enzyme being the direct precursor of the products acetyl-CoA and oxaloacetate. Consistent with these results, a previously described isotopic exchange between acetyl-CoA and [3H]CoASH, indicating the formation of an acetyl-enzyme in the reaction pathway, could not be confirmed. Substrate analogue CoA-thioethers of malate synthase are inhibitors endowed with the affinity of the substrates. Acetyl carboxylase and fatty acid synthetase are not inhibited by the substrate analogue S-ethyl-CoA; S-carboxyethyl-CoA, which could substitute for malonyl-CoA, is likewise not inhibitory. An explanation is proposed. Previously suggested roles of S-carboxymethyl-CoA, an acetyl-CoA-related inhibitor of citrate synthase, are discussed in the light of new experimental data. S-Acetyl, S-propionyl and S-carboxymethyl derivatives of 1,N6-etheno-CoA loose the high affinity of their CoA-counterparts to citrate synthase, probably because the ethylene group prevents proper binding to the enzyme.
制备了酶的底物和中间体类似物抑制剂，其中酰基辅酶A底物的硫酯氧被氢取代，形成辅酶A硫醚。用ATP柠檬酸裂解酶和S-(3,4-二羧基-3-羟基丁基)-辅酶A进行的实验表明，柠檬酸辅酶A是产物乙酰辅酶A和草酰乙酸的直接前体，而柠檬酸酶不是。与这些结果一致的是，先前描述的乙酰辅酶A和[3H]辅酶A之间的同位素交换（表明在反应途径中形成了乙酰酶）无法得到证实。苹果酸合酶的底物类似物辅酶A硫醚是具有底物亲和力的抑制剂。乙酰辅酶A羧化酶和脂肪酸合成酶不受底物类似物S-乙基辅酶A的抑制；可以替代丙二酰辅酶A的S-羧乙基辅酶A同样没有抑制作用。提出了一种解释。根据新的实验数据，讨论了先前提出的柠檬酸合酶的乙酰辅酶A相关抑制剂S-羧甲基辅酶A的作用。1,N6-乙烯基辅酶A的S-乙酰基、S-丙酰基和S-羧甲基衍生物失去了它们的辅酶A对应物对柠檬酸合酶的高亲和力，可能是因为乙烯基团阻止了与酶的正确结合。
