Yavin E, Zutra A
Biochim Biophys Acta. 1979 Jun 2;553(3):424-37. doi: 10.1016/0005-2736(79)90298-0.
The time-dependent accumulation of phosphatidyldimethylethanolamine in formaldehyde-induced vesicles obtained from a somatic cell hybrid line was investigated. From a number of considerations including a two-fold enrichment of cholesterol and sphingomyelin it was concluded that these vesicles were derived from the cell plasma membrane. A progressive depletion of phosphatidylcholine, the major vesicle phospholipid, was observed in cells supplemented for various time periods with dimethylethanolamine. This depletion was accompanied by a concomitant increase in the amount of lipid analog. The time-dependent alteration of the phospholipid polar head group in intact cells was almost identical to that observed in isolated plasma membrane vesicles, suggesting a rapid equilibration of the de novo synthesized phospholipid with the cell surface compartment. From the initial velocity rate, the time required for the phosphatidylcholine pool to double was about 12 h. Agarose-linked phospholipase A2 was used to measure the relative composition of choline- and dimethylethanolamine-phosphoglycerides in the outer surface of vesicles prepared from cells with different degrees of polar head group substitution. The gradual appearance of lysodimethylethanolamine lipid analog in vesicles treated with phospholipase A2 suggested an asymmetric distribution of the phospholipid between the interior and the exterior part of the vesicle. This asymmetry was maximal up to about 4 h following the addition of dimethylethanolamine to the culture medium and was of a transient nature as the lipid analog accumulated on both sides of the plasma membrane. Based on these measurements a fast followed by a slow translocation component could be distinguished with apparent doubling times of 7 and 43 h for the lipid analog, respectively. As the analog becomes the predominant cellular phospholipid a significant increase in the vesicle lipid fluidity was measured.
研究了从体细胞杂交系获得的甲醛诱导囊泡中磷脂酰二甲基乙醇胺的时间依赖性积累。从包括胆固醇和鞘磷脂两倍富集在内的多种因素考虑，得出这些囊泡源自细胞质膜的结论。在不同时间段用二甲基乙醇胺补充的细胞中，观察到主要囊泡磷脂磷脂酰胆碱逐渐减少。这种减少伴随着脂质类似物数量的相应增加。完整细胞中磷脂极性头部基团的时间依赖性变化与在分离的质膜囊泡中观察到的几乎相同，表明新合成的磷脂与细胞表面区室快速平衡。从初始速度率来看，磷脂酰胆碱池翻倍所需的时间约为12小时。使用琼脂糖连接的磷脂酶A2来测量由具有不同程度极性头部基团取代的细胞制备的囊泡外表面中胆碱和二甲基乙醇胺磷酸甘油酯的相对组成。用磷脂酶A2处理的囊泡中溶血二甲基乙醇胺脂质类似物的逐渐出现表明磷脂在囊泡内部和外部之间的不对称分布。在向培养基中添加二甲基乙醇胺后约4小时内，这种不对称性最大，并且随着脂质类似物在质膜两侧积累，这种不对称性是短暂的。基于这些测量，可以区分出快速随后是缓慢的转运成分，脂质类似物的表观翻倍时间分别为7小时和43小时。随着类似物成为主要的细胞磷脂，测量到囊泡脂质流动性显著增加。
