Mehlhorn I E, Florio E, Barber K R, Lordo C, Grant C W
Department of Biochemistry, University of Western Ontario, London, Canada.
Biochim Biophys Acta. 1988 Mar 22;939(1):151-9. doi: 10.1016/0005-2736(88)90056-9.
'Interdigitation' is a term coined to describe the phenomenon whereby pure phosphatidylcholines with intramolecular fatty acid chain length heterogeneity when hydrated to form bilayers may insert the methyl ends of long fatty acids from one side across more than half of the membrane thickness to protrude amongst the acyl chains of the opposite side of the bilayer (Keough, K.M.W. and Davis, P.J. (1979) Biochemistry 18, 1453-1459; Huang, C. and Mason, J.T. (1986) Biochim. Biophys. Acta 864, 423-470). In this article we address the fate of long fatty acid chains of glycosphingolipids present as minor components in membranes of non-interdigitating phosphatidylcholines. In this pursuit, derivatives of galactosyl ceramide, lactosyl ceramide, globoside and GM1 were synthesized having either 18-carbon or 24-carbon fatty acid with a spin label covalently attached at C-16. Labelled glycolipids were incorporated at 1-2 mol% into bilayers of synthetic phosphatidylcholines, their mixtures with cholesterol, or natural egg phosphatidylcholine. In each case the C-16 carbon of the glycolipid long chain fatty acid showed considerably greater 'order' and immobility than did C-16 of the fatty acid which was similar in length to the host matrix phospholipids. We interpret this as strong evidence that the long chain fatty acid interdigitates across the mid point of the bilayer in the systems studied. Clearly this phenomenon did not require that the phospholipid host matrix have mixed chain lengths. Furthermore it was totally independent of glycolipid family: for a given host matrix and (glycolipid) fatty acid chain length the order parameter values found were the same amongst all four glycolipid families tested.
“叉指化”是一个创造出来的术语，用于描述一种现象，即当具有分子内脂肪酸链长度异质性的纯磷脂酰胆碱水合形成双层时，长脂肪酸的甲基端可能从一侧插入超过膜厚度的一半，从而在双层另一侧的酰基链之间突出（基奥，K.M.W.和戴维斯，P.J.（1979年）《生物化学》18卷，第1453 - 1459页；黄，C.和梅森，J.T.（1986年）《生物化学与生物物理学报》864卷，第423 - 470页）。在本文中，我们探讨了作为非叉指化磷脂酰胆碱膜中次要成分的糖鞘脂长脂肪酸链的命运。在这一研究过程中，合成了半乳糖神经酰胺、乳糖神经酰胺、红细胞糖苷脂和GM1的衍生物，它们带有共价连接在C - 16位的自旋标记，脂肪酸链长度为18个碳或24个碳。将标记的糖脂以1 - 2摩尔百分比掺入合成磷脂酰胆碱双层、它们与胆固醇的混合物或天然鸡蛋磷脂酰胆碱中。在每种情况下，糖脂长链脂肪酸的C - 16碳显示出比与主体基质磷脂长度相似的脂肪酸的C - 16碳更大的“有序性”和流动性。我们将此解释为有力证据，表明在所研究的体系中长链脂肪酸在双层中点处发生了叉指化。显然，这种现象并不要求磷脂主体基质具有混合链长度。此外，它完全独立于糖脂家族：对于给定的主体基质和（糖脂）脂肪酸链长度，在所测试的所有四个糖脂家族中发现的序参量值是相同的。
