Spooner P J, Gantz D L, Hamilton J A, Small D M
Department of Biophysics, Boston University School of Medicine, Housman Medical Research Center, Massachusetts 02118-2394.
J Biol Chem. 1990 Jul 25;265(21):12650-5.
In the process of lipoprotein lipolysis, masses of fatty acid are generated at the surface of the lipoprotein. The newly generated fatty acid may at least partly redistribute from the site of lipolysis to phospholipid-rich membranes and to albumin. We have studied the distribution of [1-13C]oleic acid in model systems consisting of chylomicron-like triacylglycerol-rich emulsions, unilamellar phosphatidylcholine vesicles, and bovine serum albumin. By using high resolution 13C NMR spectroscopy it was possible to distinguish fatty acid in each compartment (emulsion, vesicle, albumin) and quantitate the fatty acid distribution under various conditions of lipid compartment concentration and aqueous pH. When emulsions and vesicles were present in equivalent mass amounts, fatty acid exhibited a profound preference for the lipid bilayers. The release of oleic acid to phospholipid bilayers was presumably also a function of its high molar stoichiometry (5:1) with the albumin present. More equitable distributions of fatty acid between vesicles and emulsions were seen when higher concentrations of emulsion were used. The distribution of fatty acid between compartments was in good agreement with predictions made using the apparent ionization constant, expressed as pKapp, of 7.5 and the surface to core (phospholipid to triacylglycerol) distribution coefficient of 7.0, measured for unionized oleic acid in chylomicron particles (Spooner, P. J. R., Bennett Clark, S., Gantz, D. L., Hamilton, J. A., and Small, D. M. (1988) J. Biol. Chem. 263, 1444-1455). These results indicate that the affinities of fatty acid for phospholipid bilayer and chylomicron-like emulsion surfaces are equivalent. Redistribution of lipolytically generated fatty acid from chylomicron surface to cell membrane may simply be driven by the predominant quantity of the cell membrane surfaces.
在脂蛋白脂肪分解过程中，脂蛋白表面会产生大量脂肪酸。新生成的脂肪酸可能至少部分地从脂肪分解部位重新分布到富含磷脂的膜和白蛋白中。我们研究了[1-13C]油酸在由富含乳糜微粒样三酰甘油的乳液、单层磷脂酰胆碱囊泡和牛血清白蛋白组成的模型系统中的分布。通过使用高分辨率13C核磁共振光谱，能够区分每个隔室（乳液、囊泡、白蛋白）中的脂肪酸，并在脂质隔室浓度和水相pH的各种条件下定量脂肪酸分布。当乳液和囊泡的质量相等时，脂肪酸对脂质双层表现出强烈的偏好。油酸释放到磷脂双层中可能也是由于其与存在的白蛋白的高摩尔化学计量比（5:1）。当使用更高浓度的乳液时，可以看到脂肪酸在囊泡和乳液之间的分布更加均匀。脂肪酸在隔室之间的分布与使用7.5的表观电离常数（表示为pKapp）和7.0的表面到核心（磷脂到三酰甘油）分布系数所做的预测非常吻合，这些参数是针对乳糜微粒颗粒中未电离的油酸测量得到的（Spooner, P. J. R., Bennett Clark, S., Gantz, D. L., Hamilton, J. A., and Small, D. M. (1988) J. Biol. Chem. 263, 1444 - 1,455）。这些结果表明脂肪酸对磷脂双层和乳糜微粒样乳液表面的亲和力是相当的。脂解产生的脂肪酸从乳糜微粒表面重新分布到细胞膜可能仅仅是由细胞膜表面的主要数量驱动的。
