Kramer R M, Branton D
Biochim Biophys Acta. 1979 Sep 21;556(2):219-32. doi: 10.1016/0005-2736(79)90044-0.
Phosphatidylcholine-specific exchange protein from calf liver was used to study the asymmetry and transmembrane movement of phosphatidylcholine in rat erythrocyte membranes isolated on polylysine-coated beads. While confirming previously published results for sealed ghosts, we found that for membranes attached to beads, where the cytoplasmic surface is exposed, about 36% of the total phosphatidylcholine is readily available for exchange, while the remaining 64% is exchangeable at a much slower rate. This indicates that the relative transbilayer asymmetry of phosphatidylcholine is largely maintained when red cell membranes are isolated on beads. On the other hand, transmembrane movement of phosphatidylcholine is decreased in membranes attached to cationized beads: the half-time for equilibration of phosphatidylcholine between the two monolayers of the membrane is 8 h for membranes on beads, compared to 1.5 h for sealed ghosts. Our results indicate that polylysine-derivatized beads are a useful tool for studying asymmetric properties of biological membranes.
用来自小牛肝脏的磷脂酰胆碱特异性交换蛋白研究了在聚赖氨酸包被的珠子上分离的大鼠红细胞膜中磷脂酰胆碱的不对称性和跨膜运动。在证实了先前发表的关于密封血影的结果的同时，我们发现，对于附着在珠子上且细胞质表面暴露的膜，约36%的总磷脂酰胆碱易于进行交换，而其余64%的交换速率则要慢得多。这表明，当红细胞膜在珠子上分离时，磷脂酰胆碱的相对跨膜不对称性在很大程度上得以维持。另一方面，附着在阳离子化珠子上的膜中磷脂酰胆碱的跨膜运动减少：对于珠子上的膜，磷脂酰胆碱在膜的两个单层之间达到平衡的半衰期为8小时，而对于密封血影则为1.5小时。我们的结果表明，聚赖氨酸衍生化的珠子是研究生物膜不对称性质的有用工具。
