Lim P H, Pritchard P H, Paddon H B, Vance D E
Biochim Biophys Acta. 1983 Aug 29;753(1):74-82. doi: 10.1016/0005-2760(83)90100-5.
A new model system for the study of phosphatidylcholine biosynthesis is presented. Young rats were fed a diet that contained 5% cholesterol and 2% cholate. After 6 days there was a 2-fold increase in the concentration of plasma phospholipid (243 mg/dl compared to 132 mg/dl for control animals) and a 3-fold increase in the concentration of plasma phosphatidylcholine. The rate of phosphatidylcholine biosynthesis was measured after injection of [Me-3H]choline into the portal veins. The incorporation of tritium into choline, phosphocholine and betaine by liver was similar for experimental and control animals, whereas there was a 3-fold increased incorporation into phosphatidylcholine of the cholesterol/cholate-fed rats. The activities of the enzymes of phosphatidylcholine biosynthesis in cytosol and microsomes were assayed. The only change detected was in the cytosolic and microsomal activities of CTP: phosphocholine cytidylyltransferase which were increased more than 2-fold in specific activity. When total cytidylyltransferase activity per liver was determined, a dramatic translocation of the enzyme to microsomes was observed. The control livers had 24% of the cytidylyltransferase activity associated with microsomes, whereas this value was 61% in the livers from cholesterol/cholate-fed rats. When the cytosolic cytidylyltransferase was assayed in the presence of phospholipid, the enzyme was stimulated several-fold and the difference in specific activity between control and cholesterol/cholate-fed rats was abolished. The increased activity in cytosol appears to be the result of a 2-fold increase in the amount of phospholipid in the cytosol from cholesterol/cholate-fed rats. The data strongly support the hypothesis that the special diet stimulates phosphatidylcholine biosynthesis by causing a translocation of the cytidylyltransferase from cytosol to microsomes where it is activated.
本文介绍了一种用于研究磷脂酰胆碱生物合成的新模型系统。给幼鼠喂食含有5%胆固醇和2%胆酸盐的饮食。6天后，血浆磷脂浓度增加了2倍（对照动物为132mg/dl，实验动物为243mg/dl），血浆磷脂酰胆碱浓度增加了3倍。将[甲基-3H]胆碱注入门静脉后，测量磷脂酰胆碱的生物合成速率。实验动物和对照动物肝脏对胆碱、磷酸胆碱和甜菜碱的氚掺入情况相似，而胆固醇/胆酸盐喂养的大鼠对磷脂酰胆碱的掺入增加了3倍。测定了胞质溶胶和微粒体中磷脂酰胆碱生物合成酶的活性。检测到的唯一变化是CTP：磷酸胆碱胞苷转移酶的胞质溶胶和微粒体活性，其比活性增加了2倍多。当测定每只肝脏的总胞苷转移酶活性时，观察到该酶向微粒体的显著转位。对照肝脏中与微粒体相关的胞苷转移酶活性占24%，而胆固醇/胆酸盐喂养的大鼠肝脏中这一值为61%。当在磷脂存在下测定胞质溶胶胞苷转移酶时，该酶被刺激了几倍，对照动物和胆固醇/胆酸盐喂养的大鼠之间的比活性差异消失。胞质溶胶中活性的增加似乎是胆固醇/胆酸盐喂养的大鼠胞质溶胶中磷脂量增加2倍的结果。这些数据有力地支持了这样一种假设，即特殊饮食通过导致胞苷转移酶从胞质溶胶转位到被激活的微粒体来刺激磷脂酰胆碱的生物合成。
