Backer J M, Dawidowicz E A
Nature. 1987;327(6120):341-3. doi: 10.1038/327341a0.
The endoplasmic reticulum is the principal site of synthesis and initial incorporation of membrane lipids in eukaryotic cells; the enzymes of glycerolipid biosynthesis are exclusively located on its cytoplasmic surface. To maintain a phospholipid bilayer in this organelle, newly synthesized phospholipids must be translocated to the lumenal surface. Consistent with this are measurements indicating that movement of phospholipids across microsomal membranes is rapid, with a half-time less than 5 min (refs 3 and 4). Rapid movement of phospholipids has also been detected across the plasma membrane of Bacillus megaterium, another site of de novo lipid biosynthesis. The rapid transmembrane movement of phosphatidylcholine has not been detected, however, in vesicles prepared from microsomal lipids. These latter data suggest involvement in the endoplasmic reticulum of a phospholipid-translocating protein, as was first proposed by Bretscher who called it 'flippase'. Here we report reconstitution of a phospholipid flippase from rat liver microsomes into lipid vesicles.
内质网是真核细胞中膜脂合成与初步整合的主要场所；甘油olipid生物合成的酶仅位于其细胞质表面。为了在这个细胞器中维持磷脂双层，新合成的磷脂必须转运到腔表面。与此一致的是，测量表明磷脂跨微粒体膜的移动很快，半衰期不到5分钟（参考文献3和4）。在另一个从头合成脂质的场所巨大芽孢杆菌的质膜上也检测到了磷脂的快速移动。然而，在由微粒体脂质制备的囊泡中尚未检测到磷脂酰胆碱的快速跨膜移动。后一组数据表明内质网中存在一种磷脂转运蛋白，这是布雷舍尔首次提出的，他将其称为“翻转酶”。在这里，我们报告了从大鼠肝脏微粒体中重建磷脂翻转酶到脂质囊泡中的过程。
