Carrasco M P, Segovia J L, Marco C
Department of Biochemistry and Molecular Biology, Faculty of Sciences, University of Granada, Spain.
Mol Cell Biochem. 2001 Jan;217(1-2):43-50. doi: 10.1023/a:1007271915160.
We have studied in vitro the effects of ethanol on the different enzymes involved in the biosynthesis of phosphatidylcholine (PC) via CDP-choline. Ethanol alters neither choline kinase (CK) nor CTP:phosphocholine cytidylyltransferase (CT) activities but, at levels higher than 50 mM, it does significantly inhibit microsomal cholinephosphotransferase (CPT) activity concomitantly with an increase in the ethanol concentration. A study of the kinetics of the reaction catalysed by CPT shows that ethanol decreases Vmax without altering Km, indicating a non-competitive inhibitory effect. An analysis of the thermodependence of CPT activity in the absence of ethanol reveals a break in the Arrhenius plot and thus a straight relationship between enzyme activity and the physico-chemical state of the microsomal membrane. Incubation of microsomes in the presence of ethanol increased the transition temperature from 25.8-28.2 degrees C. Microsomes were also incubated with n-alkanols with chain-lengths of fewer than five carbon atoms at concentrations which, according to their partition coefficients, produce equimolar levels in the membrane. Under these conditions all the alkanols caused the same inhibitory effect. All these results demonstrate that ethanol modulate the PC biosynthesis at the level of CPT activity and does not affect the CT enzyme. The inhibition found on CPT is clearly dependent on the alteration produced by ethanol on the hepatic microsomal membrane.
我们已经在体外研究了乙醇对通过CDP-胆碱参与磷脂酰胆碱（PC）生物合成的不同酶的影响。乙醇既不改变胆碱激酶（CK）的活性，也不改变CTP：磷酸胆碱胞苷转移酶（CT）的活性，但在高于50 mM的浓度下，它确实会显著抑制微粒体胆碱磷酸转移酶（CPT）的活性，同时乙醇浓度会增加。对CPT催化反应动力学的研究表明，乙醇降低了Vmax而不改变Km，表明存在非竞争性抑制作用。在无乙醇的情况下对CPT活性的热依赖性分析显示，阿累尼乌斯图中有一个断点，因此酶活性与微粒体膜的物理化学状态之间存在线性关系。在乙醇存在下孵育微粒体可使转变温度从25.8℃升高至28.2℃。微粒体还与链长少于五个碳原子的正构烷醇在根据其分配系数在膜中产生等摩尔水平的浓度下孵育。在这些条件下，所有的烷醇都产生相同的抑制作用。所有这些结果表明，乙醇在CPT活性水平上调节PC的生物合成，并且不影响CT酶。在CPT上发现的抑制作用显然取决于乙醇对肝微粒体膜产生的改变。
