KINETICS OF PHOSPHATIDYLCHOLINE AND LYSOPHOSPHATIDYLCHOLINE EXCHANGE BETWEEN UNILAMELLAR VESICLES
KINETICS OF PHOSPHATIDYLCHOLINE AND LYSOPHOSPHATIDYLCHOLINE EXCHANGE BETWEEN UNILAMELLAR VESICLES
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DOI：
10.1021/bi00315a017
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发表时间：
1984-01-01
期刊：
影响因子：
2.9
通讯作者：
PHILLIPS, MC
中科院分区：
文献类型：
--
作者：
MCLEAN, LR;PHILLIPS, MC
磷脂酰胆碱和溶血磷脂酰胆碱从单层供体囊泡到类似组合物的受体囊泡的交换速率在无蛋白质系统中进行，以建立交换速率和脂质的水相溶解度之间的关系。此外，在一定温度范围内检查囊泡之间的二肉豆蔻酰磷脂酰胆碱（DMPC）的交换速率，以确定脂质相变对脂质交换速率的影响。DMPC的囊泡间交换比跨双层交换快;双层外单层中的脂质分子在37 ℃下交换，t1/2 [半衰期] = 2.0小时。C.在DMPC交换的Arrhenius图中观察到不连续性;在27 ℃-28 ℃的温度范围内的活化能。45.degree. C为70 kJ mol-1。DMPC交换的t1/2外推至24.5 ℃。C（供体双层的相变温度）为6.5小时，并且从低于24 ℃的温度开始。C为82.6h。DMPC交换的活化热力学参数在24.5 ℃以上和以下的差异。C为25 kJ mol-1的活化焓和197 J/mol每K的活化熵。这些差异类似于与DMPC的凝胶到液晶相变相关的焓变和熵变。溶血棕榈酰磷脂酰胆碱（LPPC）的交换率难以测量，因为LPPC快速转移到用于分离供体和受体囊泡的柱上;转移的t1/2 < 2 min。胆固醇-鸡蛋PC囊泡中5 mol%的LPPC不影响胆固醇交换率。胆固醇、LPPC、DMPC、二棕榈酰磷脂酰胆碱和1-棕榈酰-2-油酰磷脂酰胆碱的交换速率用于计算每个分子交换的活化自由能。从自胶束到水的转移的活化自由能和自由能增加2.2和2.1 kJ/mol，每个亚甲基基团，分别。因此，转移自由能是脂质分子相对交换速率的良好预测因子。而活化自由能为30 . ±-. 1 kJ/mol >转移自由能。这种多余的自由能被认为是与限制的脂质分子的表面的囊泡在过渡态复合物。
The rates of exchange of phosphatidylcholine and lysophosphatidylcholine from unilamellar donor vesicles to acceptor vesicles of similar composition were followed in a protein-free system to establish the relationship between the rate of exchange and the aqueous-phase solubility of the lipid. Further, the rate of exchange of dimyristoylphosphatidylcholine (DMPC) between vesicles was examined over a range of temperatures to determine the effect of the lipid phase transition on the rate of lipid exchange. Intervesicular exchange of DMPC is faster than transbilayer exchange; lipid molecules in the outer monolayer of the bilayer exchange with t1/2 [half-life] = 2.0 h at 37.degree. C. A discontinuity is observed in Arrhenius plots of DMPC exchange; the activation energy over the temperature range 27.degree.-45.degree. C is 70 kJ mol-1. The t1/2 for DMPC exchange extrapolated to 24.5.degree. C (the phase transition temperature of the donor bilayer) is 6.5 h and from temperatures below 24.degree. C is 82.6 h. The differences in the thermodynamic parameters of activation for DMPC exchange above and below 24.5.degree. C are 25 kJ mol-1 for the activation enthalpy and 197 J/mol per K for the activation entropy. These differences are similar to the enthalpy and entropy changes associated with the gel to liquid-crystalline phase transition of DMPC. The rate of exchange of lysopalmitoylphosphatidylcholine (LPPC) was difficult to measure since LPPC transfers rapidly to the columns used for separating donor and acceptor vesicles; the t1/2 for transfer is < 2 min. LPPC at 5 mol% in cholesterol-egg PC vesicles does not affect the rate of cholesterol exchange. The rates of exchange of cholesterol, LPPC, DMPC, dipalmitoylphosphatidylcholine, and 1-palmitoyl-2-oleoylphosphatidylcholine were used to calculate activate free energies for exchange of each molecule. The activation free energies and free energies of transfer from self-micelles to water increase by 2.2 and 2.1 kJ/mol per methylene group, respectively. Thus, the free energy of transfer is a good predictor of the relative exchange rates of lipid molecules. However, the activation free energies are 30 .+-. 1 kJ/mol > the free energies of transfer. This excess free energy is proposed to be associated with restriction of the lipid molecule to the surface of the vesicle in the transition-state complex.