Belcher J D, Hamilton R L, Brady S E, Hornick C A, Jaeckle S, Schneider W J, Havel R J
Cardiovascular Research Institute, University of California, San Francisco 94143-0130.
Proc Natl Acad Sci U S A. 1987 Oct;84(19):6785-9. doi: 10.1073/pnas.84.19.6785.
Three distinct endosomal fractions were isolated in high purity from livers of estradiol-treated rats. Each fraction had characteristic physical and ultrastructural properties, but the lipid composition and major proteins of their membranes were similar and differed from those derived from the Golgi apparatus. Injected radioiodinated low density lipoproteins accumulated first in the fraction of intermediate density and later in the low density fraction. The latter was composed almost exclusively of lipoprotein-filled multivesicular bodies, most of which had a single membranous appendage. The fraction of intermediate density was composed of lipoprotein-filled vesicles that were smaller than multivesicular bodies and also had membranous appendages. The high density fraction was composed of membranes resembling the appendages of the two vesicular fractions. All three fractions were enriched in receptors for low density lipoproteins and asialoglycoproteins, but receptor concentrations were considerably reduced in multivesicular bodies. The fraction of intermediate density may represent the compartment of uncoupling of receptor and ligand (CURL) described by Geuze et al. [Geuze, H. J., Slot, J. W., Strous, G. J. A. M., Lodish, H. F. & Schwartz, A. L. (1983) Cell 32, 277-287]. CURL vesicles may lose some of their appendage as multivesicular bodies are formed. The high density fraction then may represent a receptor-recycling compartment.
从经雌二醇处理的大鼠肝脏中高纯度分离出三种不同的内体组分。每个组分都有独特的物理和超微结构特性，但其膜的脂质组成和主要蛋白质相似，且与源自高尔基体的那些不同。注射的放射性碘化低密度脂蛋白首先在中等密度组分中积累，随后在低密度组分中积累。后者几乎完全由充满脂蛋白的多囊泡体组成，其中大多数有单个膜性附属物。中等密度组分由比多囊泡体小且也有膜性附属物的充满脂蛋白的囊泡组成。高密度组分由类似于两个囊泡组分附属物的膜组成。所有这三个组分都富含低密度脂蛋白受体和去唾液酸糖蛋白受体，但多囊泡体中的受体浓度显著降低。中等密度组分可能代表Geuze等人[Geuze, H. J., Slot, J. W., Strous, G. J. A. M., Lodish, H. F. & Schwartz, A. L. (1983) Cell 32, 277 - 287]描述的受体与配体解偶联区室（CURL）。随着多囊泡体的形成，CURL囊泡可能会失去一些其附属物。然后高密度组分可能代表一个受体再循环区室。
