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在正常情况下,人的血浆游离胆固醇和胆固醇酯比值比较恒定,约为1:3。虽然血浆总胆固醇值经常发生变化,但这一比值基本不变。早在三十多年前,人们就注意到肝脏疾病时血浆胆固醇酯往往降低,当时认为与肝脏合成胆固醇酯减少有关。但近年研究证明胆固醇的酯化反应主要是通过血浆卵磷脂胆固醇酰基转移酶(Lecithin-cholesterol acyl transferase,简称LCAT)催化下进行的。此酶由肝脏合成后释放入血,在血浆中由高密度脂蛋白中载脂蛋白A激活。在此酶催化下,血浆游离胆固醇3′位的羟基接受卵磷脂β位上的脂酰基,生成酯键而分别转化为胆固醇酯和溶血卵磷脂(附图)。由于卵磷脂β位上结合的脂酰基多为
Under normal circumstances, the human plasma free cholesterol and cholesterol ester ratio is relatively constant, about 1: 3. Although the plasma total cholesterol values often change, but this ratio is basically unchanged. As early as more than thirty years ago, people noticed that plasma cholesterol esters tended to decrease in liver disease, which was attributed at the time to the reduction of hepatic synthesis of cholesterol esters. However, recent studies have shown that cholesterol esterification is mainly catalyzed by plasma lecithin cholesterol acyltransferase (LCAT). This enzyme is synthesized by the liver and released into the bloodstream, where it is activated by apolipoprotein A in high-density lipoproteins. Under this enzyme catalysis, the hydroxyl groups at the 3 ’position of the plasma free cholesterol accept acyl groups on the β-position of lecithin to generate ester bonds, which are respectively converted to cholesteryl ester and lysolecithin (FIG. Because the lecithin β-position on the acyl many