Alteration in the characters of CDP-choline synthetase and phospholipid-choline exchange enzyme upon choline starvation in Chinese hamster ovary cells.
Alteration in the characters of CDP-choline synthetase and phospholipid-choline exchange enzyme upon choline starvation in Chinese hamster ovary cells.
复制标题
中国仓鼠卵巢细胞胆碱饥饿时CDP-胆碱合成酶和磷脂-胆碱交换酶特性的变化。
DOI：
10.1016/s0021-9258(18)88917-7
复制
发表时间：
1985
期刊：
影响因子：
--
通讯作者：
Y. Sakakibara
中科院分区：
文献类型：
--
作者：
M. Maeda;M. Nishijima;Y. Akamatsu;Y. Sakakibara
当CHO-K1细胞在胆碱缺乏的条件下培养时，CDP-胆碱合成酶的比活性增加，相反磷脂-胆碱交换酶的活性降低，而与磷脂酰胆碱合成相关的其他三种已知酶的活性保持不变。前两种酶活性的变化发生在去除培养基中的胆碱之后。在向饥饿的细胞培养物中再补充胆碱后，改变的活性容易恢复到对照水平。胆碱饥饿后的变化对放线菌酮敏感，而恢复过程对药物不敏感。CDP-胆碱合成酶在未饥饿的对照细胞中的活性被发现在可溶性和膜级分。磷酸胆碱的可溶性组分中的酶的Km值不同于膜组分中的Km值。Asolectin使前者的Km值接近后者，并提高其Vmax值，而它几乎不影响后者的Km和Vmax值。在胆碱饥饿的细胞中，活性仅存在于膜部分中。胆碱饥饿时酶活性亚细胞分布的变化对放线菌酮敏感。改变的亚细胞分布恢复到初始状态后，再补充胆碱，甚至在放线菌酮的存在下。磷脂-胆碱交换酶的活性仅在饥饿和对照细胞的膜部分中发现。胆碱饥饿时，相对于胆碱的Vmax值和Km和Vmax值Ca 2+的酶的性质被改变。这些改变的动力学参数改变蛋黄磷脂酰胆碱，以便从那些在未饥饿的控制细胞是无法区分的。我们讨论了胆碱饥饿时这两种酶的特性变化的机制。
When CHO-K1 cells are cultivated under choline-deficient conditions, the specific activity of CDP-choline synthetase increases and conversely phospholipid-choline exchange enzyme activity decreases, whereas the other three known enzyme activities related to synthesis of phosphatidylcholine remain unchanged. The changes of the former two enzyme activities take place immediately after removal of choline from the medium. The altered activities readily revert to the control levels upon resupplementation of choline to the starved cell culture. The changes upon choline starvation are sensitive to cycloheximide, while the restoration processes are insensitive to the drug. The activity of CDP-choline synthetase in unstarved control cells is found in both the soluble and membrane fractions. The Km value of the enzyme in the soluble fraction for choline phosphate differs from that in the membrane fraction. Asolectin alters the Km value of the former to a value close to that of the latter and raises its Vmax value, whereas it hardly affects the Km and Vmax values of the latter. In choline-starved cells, the activity is exclusively found in the membrane fraction. The change in the subcellular distribution of the activity upon choline starvation is sensitive to cycloheximide. The altered subcellular distribution reverts to the initial status upon resupplementation of choline even in the presence of cycloheximide. The activity of the phospholipid-choline exchange enzyme is exclusively found in the membrane fraction for both starved and control cells. The properties of the enzyme are altered upon choline starvation with respect to the Vmax value for choline and the Km and Vmax values for Ca2+. These altered kinetic parameters are changed by egg yolk phosphatidylcholine so as to be indistinguishable from those in unstarved control cells. We discuss the mechanism of the alterations in the characters of both enzymes in response to choline starvation.