GEL TO LIQUID-CRYSTALLINE PHASE-TRANSITIONS IN WATER DISPERSIONS OF SATURATED MIXED-ACID PHOSPHATIDYLCHOLINES
GEL TO LIQUID-CRYSTALLINE PHASE-TRANSITIONS IN WATER DISPERSIONS OF SATURATED MIXED-ACID PHOSPHATIDYLCHOLINES
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DOI：
10.1021/bi00575a011
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发表时间：
1979-01-01
期刊：
影响因子：
2.9
通讯作者：
DAVIS, PJ
中科院分区：
文献类型：
--
作者：
KEOUGH, KMW;DAVIS, PJ
Mixed-acid saturated lecithins containing myristate, palmitate, and stearate chains were synthesized by [Crotalus adamanteus] phospholipase A2 digestion of the appropriate single-acid lecithin, followed by reacylation of the lysolecithin with the desired fatty acid anhydride. Variable amounts of acyl migration occurred during the syntheses. The positional isomers 1-myristoyl-2-palmitoyl-sn-glycero-3-phosphorylcholine and 2-myristoyl-1-palmitoyl-sn-glycero-3-phosphorylcholine, as well as 1-palmitoyl-2-stearoyl-sn-glycero-3-phosphorylcholine and 2-palmitoyl-1-stearoyl-sn-glycero-3-phosphorylcholine were made. The thermotropic behavior of these lipids dispersed in excess water was studied by differential scanning calorimetry. Positional isomers of mixed-acid saturated lecithins containing acids whose chain lengths differ by 2 methylene units had different gel to liquid-crystalline transition temperatures and enthalpies. For each isomeric pair of mixed-acid lecithins, the one which had the longer chain in the sn-1 position of glycerol had the lower transition temperature of the two. A partial phase diagram was prepared by use of the palmitoyl and myristoyl mixed-acid lecithins to obtain extrapolated transition temperatures for the pure lecithins without acyl migration. The gel to liquid-crystalline transition temperatures of water dispersions of 2-myristoyl-1-palmitoyl-sn-glycero-3-phosphorylcholine and 1-myristoyl-2-palmitoyl-sn-glycero-3-phosphorylcholine were 27.2 and 35.5.degree. C, respectively. A model which proposes slight differences in chain packing in the bilayer in the gel state is presented as a possible explanation for the observed differences in the thermotropic behavior of the positional isomers.
