Substrate specificity of plasma lysolecithin acyltransferase and the molecular species of lecithin formed by the reaction.
Substrate specificity of plasma lysolecithin acyltransferase and the molecular species of lecithin formed by the reaction.
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DOI：
10.1016/s0021-9258(18)89023-8
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发表时间：
1985-05
期刊：
影响因子：
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通讯作者：
P. Subbaiah;C. Chen;J. Bagdade;J. Albers
中科院分区：
文献类型：
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作者：
P. Subbaiah;C. Chen;J. Bagdade;J. Albers
人血浆卵磷脂-胆固醇酰基转移酶也在低密度脂蛋白存在下将溶血磷脂酶转化为卵磷脂。为了了解这种溶血卵磷脂酰基转移酶反应的生理重要性，我们研究了正常血浆中可用于酰化的溶血卵磷脂的分子种类和这些溶血卵磷脂中的每一种的酰化所形成的卵磷脂。含棕榈酸酯和硬脂酸酯的溶血卵磷脂通过卵磷脂-胆固醇酰基转移酶反应形成，而含油酸酯和亚油酸酯的溶血卵磷脂通过肝素后脂肪酶的作用形成。所有的天然溶血卵磷脂酯化率相当的分离酶。溶血血小板活化因子的酯化率约为溶血卵磷脂的70%，而溶血磷脂酰乙醇胺的酯化率约为溶血磷脂酶的30%。的2-酰基异构体的溶血素酰化的1-酰基异构体的程度相同，虽然相当大的异构化的前发生在孵育过程中。与酶孵育6小时后，卵磷脂和溶血磷脂的浓度没有净变化，尽管超过10%的标记溶血磷脂被转化为卵磷脂，表明内源性卵磷脂在反应中充当酰基供体。当通过高效液相色谱法分析所形成的卵磷脂的分子种类时，观察到与所使用的所有溶血卵磷脂相同的脂肪酸掺入模式。大部分放射性以降序掺入亚油酸、油酸和棕榈酸酰化形成的分子物质中。然而，在每种情况下，通过与棕榈酸酰化形成的卵磷脂具有最高的比放射性，其次是与亚油酸和油酸酰化的卵磷脂。从这些结果可以推测，该酶改变了血浆中卵磷脂的分子种类组成，而不增加总卵磷脂的净含量。
Human plasma lecithin-cholesterol acyltransferase also converts lysolecithin to lecithin in the presence of low density lipoproteins. To understand the physiological importance of this lysolecithin acyltransferase reaction, we investigated the molecular species of lysolecithin available for acylation in normal plasma and the lecithins which are formed by the acylation of each of these lysolecithins. Palmitate- and stearate-containing lysolecithins were formed by the lecithin-cholesterol acyltransferase reaction, whereas oleate- and linoleate-containing lysolecithins were formed by the action of post-heparin lipase(s). All the natural lysolecithins were esterified at comparable rates by the isolated enzyme. Lyso platelet-activating factor was esterified about 70% as efficiently as the lysolecithins, while lysophosphatidylethanolamine was esterified at about 30% the rate observed with lysolecithin. The 2-acyl isomers of lysolecithin were acylated to the same extent as the 1-acyl isomers, although considerable isomerization of the former took place during the incubation. There were no net changes in the concentrations of lecithin and lysolecithin after 6 h of incubation with the enzyme, although over 10% of the labeled lysolecithin was converted to lecithin, indicating that the endogenous lecithin serves as the acyl donor in the reaction. When the molecular species of lecithin formed were analyzed by high performance liquid chromatography, the same pattern of fatty acid incorporation was observed with all the lysolecithins used. The bulk of the radioactivity was incorporated into molecular species formed by the acylation with linoleic, oleic, and palmitic acids, in decreasing order. However, in each case, the lecithins formed by acylation with palmitic acid had the highest specific radioactivity, followed by those acylated with linoleic and oleic acids. From these results it is postulated that the enzyme alters the molecular species composition of lecithin in plasma without increasing the net amount of total lecithins.