Mörschel E, Staehelin L A
J Cell Biol. 1983 Aug;97(2):301-10. doi: 10.1083/jcb.97.2.301.
Cytochrome f/b6 and ATP synthetase (CF0-CF1) complexes from spinach chloroplasts have been reconstituted into liposomes prepared from soybean phospholipids and purified spinach galactolipids. Freeze-fracture analysis revealed homogeneous populations of particles spanning the lipid bilayers with their elongated axes perpendicular to the membrane plane. The lipid composition of the liposomes had no effect on the size of the reconstituted complexes, the average diameter of cytochrome f/b6 complex measuring 8.5 nm, and of the CF0 base piece of the ATP synthetase, 9.5 nm. When reconstituted cytochrome f/b6 complexes were cross-linked by means of antibodies prepared against the whole complex, the thus aggregated particles formed either hexagonal or square arrays. In both instances the center-to-center spacing of the particles was 8.3 nm, thereby suggesting that this value could be closer to the real diameter of the complexes than the one obtained from measuring individual particles. Assuming an ellipsoidal shape for these particles, and using a measured height of 11 nm, a molecular weight of approximately 280,000 could be calculated for the reconstituted cytochrome f/b6 complex, consistent with a dimeric configuration. In many instances the crystalline sheets of antibody-aggregated cytochrome f/b6 complexes were found to be free in the buffer solution; apparently the antibody-induced strains caused the sheet-like aggregates to pop out of the liposomal membranes. Agglutination studies of inside-out and right-side-out thylakoid vesicles revealed the antigenic determinants of the cytochrome f and cytochrome b6 polypeptides to be exposed on the inner thylakoid surface and to be present in stacked and unstacked membrane regions. The molecular weight calculated from the size of freeze-fractured CF0 base pieces was over twice the value determined by x-ray scattering data. This discrepancy may be caused by significant lipid domains within the base piece, or by an unusual fracturing behavior of the base piece in reconstituted liposomes.
菠菜叶绿体中的细胞色素f/b6和ATP合酶（CF0 - CF1）复合物已被重组到由大豆磷脂和纯化的菠菜半乳糖脂制备的脂质体中。冷冻蚀刻分析显示，粒子均匀分布在脂质双层中，其长轴垂直于膜平面。脂质体的脂质组成对重组复合物的大小没有影响，细胞色素f/b6复合物的平均直径为8.5纳米，ATP合酶的CF0基部为9.5纳米。当用针对整个复合物制备的抗体交联重组的细胞色素f/b6复合物时，如此聚集的粒子形成六边形或正方形阵列。在这两种情况下，粒子的中心间距均为8.3纳米，因此表明该值可能比通过测量单个粒子获得的值更接近复合物的实际直径。假设这些粒子为椭圆形，并使用测量的高度11纳米，可以计算出重组的细胞色素f/b6复合物的分子量约为280,000，这与二聚体结构一致。在许多情况下，发现抗体聚集的细胞色素f/b6复合物的晶体片在缓冲溶液中是游离的；显然，抗体诱导的应变导致片状聚集体从脂质体膜中弹出。对内外翻转类囊体小泡的凝集研究表明，细胞色素f和细胞色素b6多肽的抗原决定簇暴露在类囊体内部表面，并且存在于堆叠和未堆叠的膜区域。根据冷冻蚀刻CF0基部的大小计算出的分子量是通过X射线散射数据确定的值的两倍多。这种差异可能是由基部内的显著脂质结构域引起的，或者是由重组脂质体中基部的异常断裂行为引起的。
