Several aspects of the mutual solubility of the lipid components of the low-density lipoprotein of egg yolk have been investigated. The phospholipids were slightly soluble in the anhydrous triglycerides but became completely insoluble when water was present. Cholesterol showed a preference for the phospholipid phase both in the presence and absence of water. This partitioning behavior was taken to support the postulates that (i) the physicochemical properties of the lipids and their interactions with water may play a major role in controlling their spatial arrangement in the native lipoprotein, and (ii) the native lipoprotein contains a nucleus of almost pure triglyceride devoid of phospholipids which is surrounded by phospholipids and cholesterol.
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