Regulation of CTP: phosphocholine cytidylyltransferase activity in type II pneumonocytes.
Regulation of CTP: phosphocholine cytidylyltransferase activity in type II pneumonocytes.
复制标题
CTP 的调节：II 型肺细胞中磷酸胆碱胞苷酰转移酶的活性。
DOI：
10.1042/bj2320705
复制
发表时间：
1985
期刊：
影响因子：
--
通讯作者：
Bleasdale,JE
中科院分区：
文献类型：
--
作者：
Tesan,M;Anceschi,MM;Bleasdale,JE
通过耗尽细胞内的胆碱或将细胞暴露于细胞外肺表面活性剂，可以改变大鼠 II 型肺细胞的磷脂酰胆碱合成。研究了这些实验处理对调节酶 CTP：磷酸胆碱胞苷酰转移酶活性的影响。尽管 II 型肺炎细胞的胆碱消耗导致磷脂酰胆碱合成受到抑制，但胞苷酰转移酶活性（在不存在或存在添加脂质的情况下在细胞匀浆中测量）大大增加。胆碱耗尽的细胞中胞苷酰转移酶的激活是快速且特异的，并且当胆碱耗尽的细胞暴露于胆碱（但不是乙醇胺）时，胞苷酰转移酶的激活快速且完全逆转。酶活性的胆碱依赖性变化显然不是胆碱对胞苷酰转移酶直接作用的结果，并且它们在很大程度上不受环AMP类似物、油酸、亚油酸或放线菌酮的影响。胆碱耗尽的细胞中胞苷酰转移酶对 CTP（但不是磷酸胆碱）的 Km 值低于胆碱充足的细胞。胞苷酰转移酶的亚细胞重新分布也与胆碱耗尽细胞中酶的激活有关。当在添加脂质存在的情况下进行测量时，恢复的胞苷酰转移酶活性的 66.5 +/- 5.0% 在胆碱耗尽的细胞中呈颗粒状，但在胆碱充足的细胞中仅 34.1 +/- 4.5% 呈颗粒状。暴露于细胞外表面活性剂的 II 型肺细胞中颗粒胞苷酰转移酶也出现增加。然而，后一种亚细胞重新分布并不伴随胞苷酰转移酶活性的变化，即使[3H]胆碱掺入磷脂酰胆碱被大约抑制。 50%。因此，胞苷酰转移酶的亚细胞重新分布在某些条件下与酶活性的变化相关，但也可以在不导致酶活性改变的情况下发生。
Phosphatidylcholine synthesis by rat type II pneumonocytes was altered either by depleting the cells of choline or by exposing the cells to extracellular lung surfactant. Effects of these experimental treatments on the activity of a regulatory enzyme, CTP:phosphocholine cytidylyltransferase, were investigated. Although choline depletion of type II pneumonocytes resulted in inhibition of phosphatidylcholine synthesis, cytidylyltransferase activity (measured in cell homogenates in either the absence or presence of added lipids) was greatly increased. Activation of cytidylyltransferase in choline-depleted cells was rapid and specific, and was quickly and completely reversed when choline-depleted cells were exposed to choline (but not ethanolamine). Choline-dependent changes in enzymic activity were apparently not a result of direct actions of choline on cytidylyltransferase and they were largely unaffected by cyclic AMP analogues, oleic acid, linoleic acid or cycloheximide. The Km value of cytidylyltransferase for CTP (but not phosphocholine) was lower in choline-depleted cells than in choline-repleted cells. Subcellular redistribution of cytidylyltransferase also was associated with activation of the enzyme in choline-depleted cells. When measured in the presence of added lipids, 66.5 +/- 5.0% of recovered cytidylyltransferase activity was particulate in choline-depleted cells but only 34.1 +/- 4.5% was particulate in choline-repleted cells. An increase in particulate cytidylyltransferase also occurred in type II pneumonocytes that were exposed to extracellular surfactant. This latter subcellular redistribution, however, was not accompanied by a change in cytidylyltransferase activity even though incorporation of [3H]choline into phosphatidylcholine was inhibited by approx. 50%. Subcellular redistribution of cytidylyltransferase, therefore, is associated with changes in enzymic activity under some conditions, but can also occur without a resultant alteration in enzymic activity.