Rustaeus S, Lindberg K, Borén J, Olofsson S O
Department of Medical Biochemistry, University of Göteborg, Sweden.
J Biol Chem. 1995 Dec 1;270(48):28879-86. doi: 10.1074/jbc.270.48.28879.
BFA inhibited in a dose dependent way the assembly of apoB-48 very low density lipoprotein (VLDL) but allowed a normal rate of biosynthesis of the apolipoprotein and of the assembly of the dense ("high density lipoprotein (HDL)-like") apoB-48 particle (apoB-48 HDL). The inhibition of the assembly of apoB-48 VLDL occurred at BFA levels that allowed a major secretion of both transferrin and apoB-48 HDL. The assembly of apoB-100 containing lipoproteins was also inhibited by BFA but could be reactivated by a 30-60 min chase in the absence of BFA, which agreed with the time that was estimated to be needed to restore the secretory pathway (approximately 60 min). Also the assembly of apoB-48 VLDL was reversible. Both apoB-48 and apoB-100 that was labeled in the presence of BFA assembled VLDL after removal of the BFA. Both apoB-100 and apoB-48 were associated with the membrane pellet of the microsomes. Virtually all (122 +/- 30%) of the membrane associated pulse-labeled apoB-48 remained in the membrane after a 180-min chase in the presence of BFA, compared to only 21 +/- 2% in normal cells (mean +/- S.D., n = 4). The corresponding figures for apoB-100 was 40 +/- 7% in BFA-treated cells and 9 +/- 7% in normal cells (mean +/- S.D., n = 4). Pulse-chase experiments with BFA offered conditions to selectively follow the turnover of membrane-associated apoB-100. Such experiments indicated that this apoB-100 pool is a precursor to VLDL.
布雷菲德菌素A（BFA）以剂量依赖的方式抑制载脂蛋白B-48极低密度脂蛋白（VLDL）的组装，但允许载脂蛋白的生物合成速率正常以及致密的（“高密度脂蛋白（HDL）样”）载脂蛋白B-48颗粒（载脂蛋白B-48 HDL）的组装正常。载脂蛋白B-48 VLDL组装的抑制发生在BFA水平，该水平允许转铁蛋白和载脂蛋白B-48 HDL大量分泌。含载脂蛋白B-100的脂蛋白的组装也受到BFA的抑制，但在不存在BFA的情况下经过30 - 60分钟的追踪可以重新激活，这与恢复分泌途径估计所需的时间（约60分钟）一致。同样，载脂蛋白B-48 VLDL的组装也是可逆的。在去除BFA后，在BFA存在下标记的载脂蛋白B-48和载脂蛋白B-100都组装成VLDL。载脂蛋白B-100和载脂蛋白B-48都与微粒体的膜沉淀相关。在BFA存在下经过180分钟的追踪后，几乎所有（122±30%）与膜相关的脉冲标记载脂蛋白B-48仍留在膜中，而正常细胞中仅为21±2%（平均值±标准差，n = 4）。载脂蛋白B-100在BFA处理细胞中的相应数字为40±7%，在正常细胞中为9±7%（平均值±标准差，n = 4）。用BFA进行的脉冲追踪实验提供了选择性追踪膜相关载脂蛋白B-100周转的条件。此类实验表明，这个载脂蛋白B-100库是VLDL的前体。
