Lin H N, Wang Z Q, Huang C H
Department of Biochemistry, University of Virginia, Charlottesville 22908.
Biochemistry. 1990 Jul 31;29(30):7063-72. doi: 10.1021/bi00482a017.
To examine the thermotropic phase behavior of various mixed-chain phosphatidylcholines in excess water and to compare it with the known behavior of identical-chain phosphatidylcholines, we have carried out high-resolution differential scanning calorimetric (DSC) studies on aqueous dispersions of 10 different mixed-chain phosphatidylcholines. These lipids, C(16):C(18)PC, C(18):C(16)PC, C(15):C(19)PC, C(19):C(15)PC, C(14):C(20)PC, C(20):C(14)PC, C(13):C(21)PC, C(21):C(13)PC, C(12):C(22)PC, and C(22):C(12)PC, have a common molecular weight which is the same as that of C(17):C(17)PC, an identical-chain phosphatidylcholine with a molecular weight of 762.2. When the values of any of the thermodynamic parameters (Tm, delta H, and delta S) of the mixed-chain phosphatidylcholines and C(17):C(17)PC are plotted against the normalized chain-length difference (delta C/CL), a linear function with negative slope is obtained provided that the value of delta C/CL is within the range of 0.09-0.4. The linear relationship suggests that these mixed-chain phospholipids are packed in the gel-state bilayer similar to the bilayer structure of C(17):C(17)PC at T less than Tm; however, the negative slope suggests that the conformational statistics of the hydrocarbon chain and the lateral lipid-lipid interactions of these phosphatidylcholines in the gel-state bilayer are perturbed proportionally by a progressive increase in the chain-length inequivalence between the two acyl chains within each lipid molecule. When the value of delta C/CL for mixed-chain phosphatidylcholines reaches the range of 0.44-0.55, the thermotropic phase behavior deviates markedly from that of less asymmetric phosphatidylcholines, suggesting that these highly asymmetric lipids are packed into mixed interdigitated bilayers at T less than Tm. The heating and cooling pathways of aqueous dispersions prepared from the 10 mixed-chain phospholipids are also discussed.
为了研究各种混合链磷脂酰胆碱在过量水中的热致相行为，并将其与相同链磷脂酰胆碱的已知行为进行比较，我们对10种不同混合链磷脂酰胆碱的水分散体进行了高分辨率差示扫描量热法（DSC）研究。这些脂质，C(16):C(18)PC、C(18):C(16)PC、C(15):C(19)PC、C(19):C(15)PC、C(14):C(20)PC、C(20):C(14)PC、C(13):C(21)PC、C(21):C(13)PC、C(12):C(22)PC和C(22):C(12)PC，具有与C(17):C(17)PC相同的分子量，C(17):C(17)PC是一种分子量为762.2的相同链磷脂酰胆碱。当将混合链磷脂酰胆碱和C(17):C(17)PC的任何热力学参数（Tm、ΔH和ΔS）值与归一化链长差（ΔC/CL）作图时，只要ΔC/CL值在0.09 - 0.4范围内，就会得到一个斜率为负的线性函数。这种线性关系表明，在T小于Tm时，这些混合链磷脂在凝胶态双层中的堆积方式类似于C(17):C(17)PC的双层结构；然而，负斜率表明，在每个脂质分子中，两条酰基链之间链长不等价性的逐渐增加会按比例扰动这些磷脂酰胆碱在凝胶态双层中的烃链构象统计和侧向脂质-脂质相互作用。当混合链磷脂酰胆碱的ΔC/CL值达到0.44 - 0.55范围时，热致相行为明显偏离不对称性较小的磷脂酰胆碱，这表明这些高度不对称的脂质在T小于Tm时堆积成混合叉指双层。还讨论了由这10种混合链磷脂制备的水分散体的加热和冷却途径。
