Plonné D, Heller H, Kahlert U, Dargel R
Institute of Pathobiochemistry, Friedrich-Schiller University Jena, Germany.
Biochim Biophys Acta. 1995 Apr 28;1256(1):71-80. doi: 10.1016/0005-2760(95)00017-7.
Tissue pieces as well as isolated epithelial cells taken from visceral rat yolk sacs at the 18th day of gestation were able to synthesize and to secrete apo B containing lipoproteins floating in the density ranges of VLDL, IDL and LDL. In all three density classes only the high molecular weight apo B was detectable. VLDL secreted from yolk sac tissue or isolated epithelial cells lacked apo E and apo C. Studies with cycloheximide revealed that about 77% of the particles was delivered from a pool of preformed lipoproteins. Evidence was given that also de novo-synthesis of apo B containing lipoproteins took place in the tissue segments and the isolated epithelial cells. Most of apo B mass (90%) and of apo B radioactivity (60%) secreted by the tissue pieces of the visceral yolk sac floated in the density range 1.020-1.064 g/ml, the remainder being found in the d < or = 1.020 g/ml fraction. In contrast, only 40% of apo B mass and 45% of apo B radioactivity delivered from isolated epithelial cells belonged to the d = 1.020-1.064 g/ml fraction. LDL released from yolk sacs and isolated epithelial cells contained more triacylglycerols (41% vs. 25%) and had a larger mean diameter (24 nm vs. 21.8 nm) than those obtained from fetal rat serum, whereas the comparatively small VLDL produced in vitro (mean diameter = 34 nm) contained less triacylglycerols (46% vs. 60.5%) and more protein (20% vs. 10.2%) in comparison with fetal serum VLDL (mean diameter = 42.3 nm). Incubation experiments with [125I]VLDL led to the conclusion that the lipase secreted by yolk sac tissue into the medium could not be responsible for the conversion of VLDL into LDL, thus supporting our view of a direct LDL secretion by visceral rat yolk sacs.
取自妊娠第18天大鼠内脏卵黄囊的组织块以及分离的上皮细胞能够合成并分泌含载脂蛋白B的脂蛋白，这些脂蛋白漂浮在极低密度脂蛋白（VLDL）、中间密度脂蛋白（IDL）和低密度脂蛋白（LDL）的密度范围内。在所有这三个密度类别中，仅可检测到高分子量的载脂蛋白B。卵黄囊组织或分离的上皮细胞分泌的VLDL缺乏载脂蛋白E和载脂蛋白C。用环己酰亚胺进行的研究表明，约77%的颗粒来自预先形成的脂蛋白池。有证据表明，含载脂蛋白B的脂蛋白也在组织片段和分离的上皮细胞中进行从头合成。内脏卵黄囊组织块分泌的大部分载脂蛋白B质量（90%）和载脂蛋白B放射性（60%）漂浮在密度范围1.020 - 1.064 g/ml内，其余部分存在于密度d≤1.020 g/ml的组分中。相比之下，从分离的上皮细胞释放的载脂蛋白B质量的40%和载脂蛋白B放射性的45%属于密度d = 1.020 - 1.064 g/ml的组分。从卵黄囊和分离的上皮细胞释放的LDL比从胎鼠血清中获得的LDL含有更多的三酰甘油（41%对25%）且平均直径更大（24 nm对21.8 nm），而体外产生的相对较小的VLDL（平均直径 = 34 nm）与胎鼠血清VLDL（平均直径 = 42.3 nm）相比，含有较少的三酰甘油（46%对60.5%）和更多的蛋白质（20%对10.2%）。用[125I]VLDL进行的孵育实验得出结论，卵黄囊组织分泌到培养基中的脂肪酶不可能是VLDL转化为LDL的原因，从而支持了我们关于大鼠内脏卵黄囊直接分泌LDL的观点。
