Heuson-Stiennon J A, Wanson J C, Drochmans P
J Cell Biol. 1972 Nov;55(2):471-88. doi: 10.1083/jcb.55.2.471.
The sarcoplasmic reticulum (SR) of rabbit skeletal muscle was studied after isolation of a vesicle fraction and of vesicular subfractions by means of differential and density gradient centrifugations. The different fractions were examined electron microscopically by negative and positive staining; their content in protein and phospholipid and their ability to bind Ca(++) were determined. After homogenization, differential centrifugation yielded a "sarcovesicular fraction" (SVF) which was mainly composed of numerous vesicles of different types mixed with fibrous proteins and mitochondrial fragments. This SVF contained 2% of the protein and 25% of the phospholipid of the initial tissue extract. It had a high Ca(++) binding activity that was preserved for several days by storage in the presence of oxalate. After centrifugations of the SVF on sucrose density gradients, two vesicular subfractions were obtained which were characterized by different sedimentation rates, isopycnic banding, morphology, and composition in protein and phospholipid. (a) The low-density subfraction (rho 1.10-1.12) contained a heterogeneous population of membranous structures: thick- and thin-walled vesicles, tubular formations, triads, and plasma membranes. Its content in protein and phospholipid was very low. (b) The high-density subfraction (rho 1.13-1.17) was a very pure subfraction composed only of thin-walled vesicles. Its content in phospholipid was high and the ratio of phospholipid-phosphorus to protein was about 20. The calcium-binding activity found in the total SVF was recovered only in this latter homogeneous subfraction. The origin of these two subfractions from the SR is discussed.
通过差速离心和密度梯度离心分离出囊泡组分和囊泡亚组分后，对兔骨骼肌的肌浆网（SR）进行了研究。通过负染和正染对不同组分进行电子显微镜检查；测定了它们的蛋白质和磷脂含量以及结合Ca(++)的能力。匀浆后，差速离心得到一个“肌浆囊泡组分”（SVF），它主要由许多不同类型的囊泡与纤维蛋白和线粒体片段混合组成。该SVF含有初始组织提取物中2%的蛋白质和25%的磷脂。它具有高Ca(++)结合活性，在草酸盐存在下储存数天仍能保持。将SVF在蔗糖密度梯度上离心后，得到两个囊泡亚组分，其特征在于沉降速率、等密度带、形态以及蛋白质和磷脂组成不同。(a)低密度亚组分（ρ 1.10 - 1.12）包含异质的膜结构群体：厚壁和薄壁囊泡、管状结构、三联体和质膜。其蛋白质和磷脂含量非常低。(b)高密度亚组分（ρ 1.13 - 1.17）是一个非常纯的亚组分，仅由薄壁囊泡组成。其磷脂含量高，磷脂磷与蛋白质的比例约为20。在整个SVF中发现的钙结合活性仅在后者这个均匀的亚组分中恢复。讨论了这两个亚组分源自SR的情况。
