Hamilton R L, Williams M C, Fielding C J, Havel R J
J Clin Invest. 1976 Sep;58(3):667-80. doi: 10.1172/JCI108513.
Rat livers were perfused for 6 h without added plasma proteins using washed erythrocytes and buffer in a recirculating system. An inhibitor to the enzyme lecithin-cholesterol acyltransferase (5,5'-dithionitrobenzoic acid) was added in some experiments to prevent modification of substrate-lipids contained in secreted lipoproteins. The inhibitor did not detectably alter hepatic ultrastructure or gas exchange, but it inhibited the secreted lecithin-cholesterol acyltransferase by more than 85%. Very low density lipoproteins in perfusate were unaltered but the high density lipoproteins obtained from livers perfused with the inhibitor appeared disk-shaped in negative stain by electron microscopy with a mean edge thickness of 46 +/- 5 A and a mean diameter of 190 +/- 25 A. The high density lipoproteins were composed predominantly of polar lipids and protein with only small amounts of cholesteryl esters and triglycerides. The major apoprotein of these discoidal fractions had the same electrophoretic mobility as the arginine-rich apoprotein, whereas plasma high density lipoproteins contained mainly the A-I approtein. In all these respects the discoidal perfusate high density lipoproteins closely resemble those found in human plasma which is deficient in lecithin-cholesterol acyltransferase. Perfusate high density lipoproteins obtained in the absence of the enzyme inhibitor more closely resembled plasma high density lipoproteins in chemical composition (content of cholesteryl esters and apoproteins) and in electron microscopic appearance. Purified lecithin-cholesterol acyltransferase synthesized cholesteryl esters at a substantially faster rate from substrate lipids of perfusate high density lipoproteins than those from plasma. The discoidal high density lipoproteins were the best substrate for this reaction. Thin sections of plasma high density lipoproteins indicated a spherical particle whereas discoidal high density lipoproteins stained with the characteristic trilaminar image of membranes. These observations suggest that the liver secretes disk-shaped lipid bilayer particles which represent both the nascent form of high density lipoproteins and preferred substrate for lecithin-cholesterol acyltransferase.
在循环系统中，使用洗涤过的红细胞和缓冲液对大鼠肝脏进行6小时灌注，不添加血浆蛋白。在一些实验中添加了一种卵磷脂胆固醇酰基转移酶抑制剂（5,5'-二硫代硝基苯甲酸），以防止分泌的脂蛋白中所含底物脂质的修饰。该抑制剂未显著改变肝脏超微结构或气体交换，但它抑制分泌的卵磷脂胆固醇酰基转移酶超过85%。灌注液中的极低密度脂蛋白未发生改变，但用该抑制剂灌注肝脏后获得的高密度脂蛋白在电子显微镜负染下呈盘状，平均边缘厚度为46±5埃，平均直径为190±25埃。高密度脂蛋白主要由极性脂质和蛋白质组成，仅含有少量胆固醇酯和甘油三酯。这些盘状组分的主要载脂蛋白具有与富含精氨酸的载脂蛋白相同的电泳迁移率，而血浆高密度脂蛋白主要含有A-I载脂蛋白。在所有这些方面，盘状灌注液高密度脂蛋白与在缺乏卵磷脂胆固醇酰基转移酶的人血浆中发现的高密度脂蛋白非常相似。在没有酶抑制剂的情况下获得的灌注液高密度脂蛋白在化学组成（胆固醇酯和载脂蛋白含量）和电子显微镜外观上更类似于血浆高密度脂蛋白。纯化的卵磷脂胆固醇酰基转移酶从灌注液高密度脂蛋白的底物脂质合成胆固醇酯的速度比从血浆中合成的速度快得多。盘状高密度脂蛋白是该反应的最佳底物。血浆高密度脂蛋白的薄片显示为球形颗粒，而盘状高密度脂蛋白则呈现出特征性的膜的三层图像染色。这些观察结果表明，肝脏分泌盘状脂质双层颗粒，它们代表高密度脂蛋白的新生形式以及卵磷脂胆固醇酰基转移酶的优选底物。
