High resolution nuclear magnetic resonance studies of hen's egg yolk plasma lipoproteins

Abstract

High resolution nuclear magnetic resonance spectra of native or protease-treated hen's egg yolk plasma (very low density lipoproteins) were taken either in water or deuterated water; the protease-treated samples showed a sharpening of choline methyl proton signal of phospholipid, indicating the hindrance of the choline head-group rotation by the phospholipids in the native very low density lipoproteins. With both native and the protease-treated egg yolk plasma, elevated temperatue increased the signal intensity and produced line-sharpening of Q choline methyl protons and the - CH₂-C=O-protons of the methylene group adjacent to the carboxyl group of esterified fatty acids, indicating prior restriction of mobility of these groups. Total extracted lipids of egg yolk plasma containing traces of chloroform, methanol and water (which keep the sample in one phase) also gave similar temperature dependence. Addition of water to the same sample and sonication resulted in the loss of temperature dependence. Frozen and thawed protease-treated egg yolk plasma also behaved in a similar manner. The absence of temperature dependence in these latter two samples is believed to be due to formation of bilayers of phospholipids following phase separation of triglycerides and phospholipids. The results support a model in which the lipoprotein particles of the egg yolk plasma have a lipid-core structure containing triglycerides in the centre with a monomolecular layer of lecithin at the surface, the polar heads of which are surrounded by proteins.