Nichols A V, Gong E L, Blanche P J, Forte T M, Shore V G
Biochim Biophys Acta. 1984 May 11;793(3):325-37. doi: 10.1016/0005-2760(84)90246-7.
Conversion of model discoidal complexes of egg yolk phosphatidylcholine and apolipoprotein A-I, upon interaction with a source of lecithin:cholesterol acyltransferase (plasma d greater than or equal to 1.21 g/ml fraction or partially purified enzyme) and with different sources of substrate unesterified cholesterol (LDL, VLDL or cholesterol incorporated into complexes), was investigated by gradient gel electrophoresis, gel filtration, equilibrium density gradient ultracentrifugation, electron microscopy and chemical analysis. When the incubation mixture contained an inhibitor of lecithin:cholesterol acyltransferase, discoidal complexes with mean long dimension of approximately 10.5 +/- 1.9 nm were converted (within 1 h) predominantly to small round particles and were partially depleted of their phospholipid content. Upon electrophoresis the small particles showed peak maxima within the migration intervals of the human plasma ( HDL3b ) gge and ( HDL3c ) gge subpopulations with associated particle size ranges of 7.8-8.2 and 7.2-7.8 nm, respectively. Within 1 h, in the presence of activated enzyme, the complexes were again converted in major part to the small particles. However, further incubation resulted in an apparent single-step conversion to a larger major product with peak maximum occurring within the migration intervals of the ( HDL2a ) gge and the ( HDL3a ) gge subpopulations (particle size ranges 8.8-9.8 and 8.2-8.8 nm, respectively). Formation of an apolar core was indicated by detection of cholesteryl esters in the conversion product. The form in which the substrate unesterified cholesterol was introduced did not markedly influence the size properties of the final conversion product. With VLDL as source of substrate, considerable incorporation of triacylglycerol occurred in company with a lower level of cholesteryl esters, suggesting transfer of these lipids during formation of the apolar core. Incubation of complexes with a partially purified (3000-fold) preparation of lecithin:cholesterol acyltransferase yielded a product similar in properties to that when the d greater than or equal to 1.21 g/ml fraction was used. Our model discoidal complexes and their conversion products exhibit properties very similar to those of potential precursors to HDL as well as of mature HDL particles. Their further investigation shows promise of providing detailed insight into the possible origin and heterogeneity of human plasma HDL.
通过梯度凝胶电泳、凝胶过滤、平衡密度梯度超速离心、电子显微镜和化学分析，研究了蛋黄磷脂酰胆碱和载脂蛋白A-I的模型盘状复合物与卵磷脂胆固醇酰基转移酶来源（血浆d≥1.21 g/ml部分或部分纯化的酶）以及不同来源的底物未酯化胆固醇（低密度脂蛋白、极低密度脂蛋白或掺入复合物中的胆固醇）相互作用时的转化情况。当孵育混合物含有卵磷脂胆固醇酰基转移酶抑制剂时，平均长径约为10.5±1.9 nm的盘状复合物在1小时内主要转化为小圆形颗粒，其磷脂含量部分减少。电泳时，小颗粒在人血浆（HDL3b）gge和（HDL3c）gge亚群的迁移区间内显示出峰最大值，相关粒径范围分别为7.8 - 8.2 nm和7.2 - 7.8 nm。在1小时内，在活化酶存在的情况下，复合物再次大部分转化为小颗粒。然而，进一步孵育导致明显的单步转化为更大的主要产物，其峰最大值出现在（HDL2a）gge和（HDL3a）gge亚群的迁移区间内（粒径范围分别为8.8 - 9.8 nm和8.2 - 8.8 nm）。在转化产物中检测到胆固醇酯表明形成了非极性核心。引入底物未酯化胆固醇的形式对最终转化产物的大小特性没有明显影响。以极低密度脂蛋白作为底物来源时，伴随着较低水平的胆固醇酯，大量三酰甘油发生掺入，这表明在非极性核心形成过程中这些脂质发生了转移。用部分纯化（3000倍）的卵磷脂胆固醇酰基转移酶制剂孵育复合物，得到的产物性质与使用d≥1.21 g/ml部分时相似。我们的模型盘状复合物及其转化产物表现出与高密度脂蛋白潜在前体以及成熟高密度脂蛋白颗粒非常相似的性质。对它们的进一步研究有望深入了解人血浆高密度脂蛋白可能的起源和异质性。
