Chajek T, Eisenberg S
J Clin Invest. 1978 Jun;61(6):1654-65. doi: 10.1172/JCI109086.
The fate of rat plasma very low density lipoprotein (VLDL) constituents was determined in the isolated perfused rat heart. VLDL was labeled with [(14)C]palmitate, (32)P-phospholipids, [(3)H] cholesterol, and (125)I-apolipoprotein C (apoC). Perfusions were performed with an albumin-containing buffer and without plasma. Radioactivity was followed in fractions of d < 1.019, d 1.019-1.04, d 1.04-1.21, and d > 1.21 g/ml, prepared by ultracentrifugation.VLDL triglycerides were progressively hydrolyzed to fatty acids (10-120-min perfusions). Concomitantly, phospholipids, cholesterol (predominantly unesterified), and apoC were removed from the VLDL to all other fractions. About 30-35% of the phosphatidylcholine was hydrolized to lysophosphatidylcholine and was recovered at d > 1.21 g/ml. The phosphatidylcholine-and triglyceride-hydrolyzing activities were confined to membrane supported enzyme(s). The other 60-65% of the phosphatidylcholine was removed unhydrolyzed and was found in fractions of d 1.019-1.04 (10-15%), d 1.04-1.21 (25-30%), and d > 1.21 g/ml (15-20%). [(32)P]Sphingomyelin accumulated at the fraction of d 1.04-1.21 g/ml. Unesterified cholesterol was found in the fraction of d 1.04-1.21 g/ml. ApoC was recovered predominantly in fractions of d 1.04-1.21 (50-60%) and d > 1.21 g/ml (30-40%). Cholesteryl esters were associated with VLDL during the hydrolysis of 50-70% of the triglycerides, but with advanced lipolysis, appeared in higher densities, mainly d 1.019-1.04 g/ml. The fraction of d 1.04-1.21 g/ml, (containing phosphatidylcholine, sphingomyelin, unesterified cholesterol, and apoC) contained by negative staining, many disk-like structures. The study demonstrated that removal of surface constituents (phospholipids, unesterified cholesterol, and apoC) during lipolysis of VLDL is an intrinsic feature of the lipolytic process, and is independent of the presence of plasma. It also indicated that surface constituents may be removed in a particulated form.
在离体灌注的大鼠心脏中测定了大鼠血浆极低密度脂蛋白（VLDL）成分的命运。用[（14）C]棕榈酸、（32）P - 磷脂、[（3）H]胆固醇和（125）I - 载脂蛋白C（apoC）标记VLDL。分别在含有白蛋白的缓冲液和无血浆的条件下进行灌注。通过超速离心制备密度小于1.019、1.019 - 1.04、1.04 - 1.21和大于1.21 g/ml的组分，并跟踪其中的放射性。VLDL甘油三酯逐渐水解为脂肪酸（灌注10 - 120分钟）。与此同时，磷脂、胆固醇（主要是未酯化的）和apoC从VLDL转移到所有其他组分中。约30 - 35%的磷脂酰胆碱水解为溶血磷脂酰胆碱，并在密度大于1.21 g/ml的组分中回收。磷脂酰胆碱和甘油三酯的水解活性局限于膜支持的酶。另外60 - 65%的磷脂酰胆碱未水解而被去除，分别在密度为1.019 - 1.04（10 - 15%）、1.04 - 1.21（25 - 30%）和大于1.21 g/ml（15 - 20%）的组分中被发现。[（32）P]鞘磷脂在密度为1.04 - 1.21 g/ml的组分中积累。未酯化的胆固醇在密度为1.04 - 1.21 g/ml的组分中被发现。apoC主要在密度为1.04 - 1.21（50 - 60%）和大于1.21 g/ml（30 - 40%）的组分中回收。在甘油三酯水解50 - 70%的过程中，胆固醇酯与VLDL相关，但随着脂解作用的推进，出现在更高密度的组分中，主要是密度为1.019 - 1.04 g/ml的组分。密度为1.04 - 1.21 g/ml的组分（含有磷脂酰胆碱、鞘磷脂、未酯化的胆固醇和apoC）经负染色后含有许多盘状结构。该研究表明，VLDL脂解过程中表面成分（磷脂、未酯化的胆固醇和apoC）的去除是脂解过程的一个内在特征，且与血浆的存在无关。研究还表明，表面成分可能以颗粒形式被去除。
