Ting-Beall H P, Burgess F M, Dux L, Martonosi A
J Muscle Res Cell Motil. 1987 Jun;8(3):252-9. doi: 10.1007/BF01574593.
Two distinct forms of Ca2+-ATPase crystals have been analysed in sarcoplasmic reticulum (SR) membranes. The E1-type crystals, induced by Ca2+ or lanthanide ions, consist of single chains of ATPase monomers, and the E2-type crystals, induced by vanadate ions, consist of dimer chains. Using improved freeze-fracture techniques we have obtained high-resolution images of complementary surface replicas of SR membranes containing these crystal forms. In E1 crystals, the concave fracture (P) faces display obliquely oriented rows of intramembrane particles (IMPs) spaced at congruent to 6-7 nm along both crystal axes, while the convex fracture (E) faces show corresponding rows of pits. In E2 crystals, regular arrays of oblique parallel ridges with spacing of congruent to 10.5-11 nm appear on the P-faces and complementary grooves or furrows on the E-faces. In many instances the ridges break up into elongated particles repeating every 5.5 nm. When the direction of the shadow is almost parallel to the axis of the ridges, these 9.5 nm particles can be resolved into two domains, which represent intramembranous contacts between the two monomers of the two adjacent dimer chains. Complementary grooves on the E-faces can also be resolved into rows of pits complementary to the particles of the ridges on the P-faces. In the control SR membranes, randomly dispersed IMPs and corresponding pits are observed on the P- and E-faces, respectively. The data suggest that transport of Ca2+ involves significant structural changes of the enzyme molecule, reflected in the ATPase-ATPase interactions both on the cytoplasmic surface and in the lipid bilayer.
已对肌浆网（SR）膜中两种不同形式的Ca2 + -ATPase晶体进行了分析。由Ca2 +或镧系离子诱导形成的E1型晶体由ATPase单体的单链组成，而由钒酸盐离子诱导形成的E2型晶体由二聚体链组成。使用改进的冷冻断裂技术，我们获得了含有这些晶体形式的SR膜互补表面复制品的高分辨率图像。在E1晶体中，凹面断裂（P）面显示出沿两个晶体轴间距约为6 - 7 nm的倾斜排列的膜内颗粒（IMP）排，而凸面断裂（E）面显示出相应的凹坑排。在E2晶体中，P面上出现间距约为10.5 - 11 nm的规则倾斜平行脊阵列，E面上出现互补的凹槽或沟。在许多情况下，这些脊会分解成每隔5.5 nm重复的细长颗粒。当阴影方向几乎平行于脊的轴时，这些9.5 nm的颗粒可分解为两个结构域，它们代表两个相邻二聚体链的两个单体之间的膜内接触。E面上的互补凹槽也可分解为与P面上脊颗粒互补的凹坑排。在对照SR膜中，分别在P面和E面上观察到随机分散的IMP和相应的凹坑。数据表明，Ca2 +的转运涉及酶分子的显著结构变化，这反映在细胞质表面和脂质双层中的ATPase - ATPase相互作用上。
