Noel S P, Rubinstein D
J Lipid Res. 1974 Jul;15(4):301-8.
The incorporation of labeled amino acids into the peptides of very low density lipoproteins (VLDL) and high density lipoproteins (HDL) secreted by perfused rat liver was studied using a Ringer-albumin solution in the perfusate in place of serum to diminish exchange of peptides between VLDL and HDL. Among the lipoproteins, the greatest release of protein, greatest incorporation of amino acid, and highest specific activity were found in VLDL. After separation of the delipidated peptides by electrophoresis on polyacrylamide gel, the incorporation into VLDL peptides was found to be 5-10 times as great as into HDL peptides. There was virtually no incorporation into the peptides of low density lipoproteins (LDL). Approximately 25% of the radioactivity incorporated into perfusate VLDL failed to enter the 13% polyacrylamide gel. The remaining radioactivity was distributed primarily among three peptide bands; one, found in the upper portion of the gel, contained 45% of the total, most of the remainder being found in two rapidly migrating bands. These three peptides appear to approximate those of human apo-C in relative electrophoretic mobility. Most of the HDL peptide radioactivity entering the running gel was found in a band that migrates slightly faster than the main VLDL band. A portion of the radioactivity of this major HDL band did not enter the running gel unless beta-mercaptoethanol was present. Greater separation of these two bands by polyacrylamide gel electrophoresis for 24 hr confirmed that the major bands in VLDL and in HDL were different. The rapidly moving peptides of HDL were found to contain very little radioactivity. Determination of the intensity of staining of carrier-free perfusate VLDL and HDL peptides produced a pattern similar to the incorporation of labeled amino acids. It is concluded that the rapidly moving peptides, which may contain activators of lipoprotein lipase, are only secreted as part of the VLDL.
利用灌注液中的林格氏白蛋白溶液替代血清，以减少极低密度脂蛋白（VLDL）和高密度脂蛋白（HDL）之间肽的交换，研究了灌注大鼠肝脏分泌的极低密度脂蛋白和高密度脂蛋白肽中标记氨基酸的掺入情况。在脂蛋白中，VLDL的蛋白质释放量最大、氨基酸掺入量最大且比活性最高。通过聚丙烯酰胺凝胶电泳分离脱脂肽后，发现VLDL肽中的掺入量是HDL肽中的5至10倍。低密度脂蛋白（LDL）肽中几乎没有掺入。掺入灌注液VLDL中的放射性约25%未进入13%的聚丙烯酰胺凝胶。其余放射性主要分布在三个肽带中；一个位于凝胶上部，占总量的45%，其余大部分位于两个快速迁移的带中。这三种肽在相对电泳迁移率上似乎与人类载脂蛋白C的肽相近。进入电泳凝胶的大多数HDL肽放射性位于一个迁移速度略快于主要VLDL带的条带中。除非存在β-巯基乙醇，否则这个主要HDL带的一部分放射性不会进入电泳凝胶。通过聚丙烯酰胺凝胶电泳24小时对这两个带进行更大程度的分离，证实了VLDL和HDL中的主要条带是不同的。发现HDL快速迁移的肽含有的放射性很少。对无载体灌注液VLDL和HDL肽染色强度的测定产生了与标记氨基酸掺入相似的模式。得出的结论是，可能含有脂蛋白脂肪酶激活剂的快速迁移肽仅作为VLDL的一部分分泌。
