ENZYMIC REACTIONS OF MODEL PLASMA LIPOPROTEINS

卵磷脂：胆固醇酰基转移酶（LCAT）是主要的胆固醇 人血浆的酯化活性。在改造中很重要 新生高密度脂蛋白（HDL），富含游离 胆固醇，转化为成熟的高密度脂蛋白，其中大部分胆固醇在其 酯化形式。这个过程对于胆固醇的运输很重要 从周围组织到肝脏，其中一部分胆固醇如果 转化为胆汁盐。这种“胆固醇逆向转运”是 预防和消退动脉粥样硬化的重要一步。这个 项目将重点关注两个重要领域； LCAT调节和结构- 函数关系。第一步是在老鼠身上进行研究， 离体大鼠肝细胞和人肝癌细胞饮食的影响 已知影响血浆 LCAT 水平的物质对 LCAT mRNA、合成、 和分泌。膳食中含有 n-3 脂肪的甘油三酯的影响 酸，改变人体血浆 LCAT 水平，血浆 LCAT 水平，LCAT 分泌和营业额将与给予的对照大鼠进行比较 传统食物或含有 n-9 脂肪酸的甘油三酯。人类文化 将使用肝癌细胞直接比较n-3和n-6的效果 白蛋白复合物和模型重组 HDL 中的脂肪酸，其中 测试脂肪酸位于磷脂酰胆碱的 sn-2 位置。 游离胆固醇和胆固醇酯含量的影响 HDL 模型也将被确定。第二步是使用 site- 定向诱变和单克隆抗体可以明确识别 LCAT 的一些功能区域并确定其分子基础 其底物特异性，在不同的哺乳动物中是不同的 种。这些研究将描述 LCAT 形成的机制 胆固醇酯，更好地定位负责结合的区域 脂蛋白表面，并揭示活性位点区域的差异 来自具有不同底物特异性的不同物种的 LCAT。

Lecithin:cholesterol acyltransferase (LCAT) is the major cholesterol esterifying activity of human plasma. It is important in the remodeling of nascent high density lipoproteins (HDL), which are rich in free cholesterol, into mature HDL in which most of the cholesterol is in its esterified form. This process is important in the transport of cholesterol from peripheral tissues to the liver where a portion of the cholesterol if converted to bile salts. This "reverse cholesterol transport" is an important step in prevention and regression of atherosclerosis. This project will focus upon two important areas; LCAT regulation and structure- function relationships. The first step will be to investigate in rats, isolated rat hepatocytes, and human hepatoma cells the influence that diets which are known to affect plasma LCAT levels have on LCAT mRNA, synthesis, and secretion. The effects of dietary triglycerides containing n-3 fatty acids, which alter plasma LCAT levels in man, on plasma LCAT levels, LCAT secretion, and turnover will be compared with those of control rats given conventional chow or triglycerides with n-9 fatty acids. Cultures of human hepatoma cells will be used to directly compared the effects of n-3 and n-6 fatty acids in albumin complexes and in model reassembled HDL in which the test fatty acids are located at the sn-2 position of phosphatidylcholine. The effects of the free cholesterol and cholesteryl ester contents of the model HDL will also be determined. The second step will be to use site- directed mutagenesis and monoclonal antibodies to unambiguously identify some of the functional regions of LCAT and to determine the molecular basis of its substrate specificity, which is different in different mammalian species. These studies will delineate the mechanism by which LCAT forms cholesteryl esters, better localize the region(s) responsible for binding to lipoprotein surfaces, and reveal differences in the active site region of LCAT from different species that have different substrate specificities.