Cornelius F
Department of Biophysics, University of Aarhus, DK-8000 Denmark.
Biochemistry. 2001 Jul 31;40(30):8842-51. doi: 10.1021/bi010541g.
The effects of phospholipid acyl chain length (n(c)), degree of acyl chain saturation, and cholesterol on Na,K-ATPase reconstituted into liposomes of defined lipid composition are described. The optimal acyl chain length of monounsaturated phosphatidylcholine in the absence of cholesterol was found to be 22 but decreased to 18 in the presence of 40 mol % cholesterol. This indicates that the hydrophobic matching of the lipid bilayer and the transmembrane hydrophobic core of the membrane protein is a crucial parameter in supporting optimal Na,K-ATPase activity. In addition, the increased bilayer order induced by both cholesterol and saturated phospholipids could be important for the conformational mobility of the Na,K-ATPase changing the distribution of conformations. Lipid fluidity was important for several parameters of reconstitution, e.g., the amount of protein inserted and the orientation in the liposomes. The temperature dependence of the Na,K-ATPase as well of the Na-ATPase reactions depends both on phospholipid acyl chain length and on cholesterol. Cholesterol increased significantly both the enthalpy of activation and entropy of activation for Na,K-ATPase activity and Na-ATPase activity of Na,K-ATPase reconstituted with monounsaturated phospholipids. In the presence of cholesterol the free energy of activation was minimum at a lipid acyl chain length of 18, the same that supported maximum turnover. In the case of ATPase reconstituted without cholesterol, the minimum free energy of activation and the maximum turnover both shifted to longer acyl chain lengths of about 22.
本文描述了磷脂酰基链长度（(n(c))）、酰基链饱和度以及胆固醇对重构于特定脂质组成脂质体中的钠钾-ATP酶的影响。发现在不存在胆固醇的情况下，单不饱和磷脂酰胆碱的最佳酰基链长度为22，但在存在40摩尔%胆固醇时降至18。这表明脂质双层与膜蛋白跨膜疏水核心的疏水匹配是支持最佳钠钾-ATP酶活性的关键参数。此外，胆固醇和饱和磷脂诱导的双层有序性增加对于钠钾-ATP酶构象迁移率改变构象分布可能很重要。脂质流动性对于重构的几个参数很重要，例如插入的蛋白量和在脂质体中的取向。钠钾-ATP酶以及钠-ATP酶反应的温度依赖性既取决于磷脂酰基链长度，也取决于胆固醇。胆固醇显著增加了用单不饱和磷脂重构的钠钾-ATP酶的钠钾-ATP酶活性和钠-ATP酶活性的活化焓和活化熵。在存在胆固醇的情况下，活化自由能在脂质酰基链长度为18时最小，这与支持最大周转率的长度相同。在没有胆固醇重构的ATP酶的情况下，活化自由能最小值和最大周转率都转移到约22的更长酰基链长度。
