Abstract
The interaction of sonicated, small vesicles of egg phosphatidylcholine and cholesterol (2:1, mol/mol) with bovine high density serum lipoproteins was examined in terms of lipid transfer between both types of particles and the resulting changes in lipoprotein structure. Saturation of high density lipoprotein preparations with vesicle lipids gave final lipoprotein particles with essentially unchanged protein content and composition, unchanged cholesterylester and nonpolar lipid content, but with markedly increased phospholipid content (59% increas by weight) and moderately increased cholesterol content (20% increase by weight). The lipoproteins enriched in lipid were relatively uniform, spherical particles, 110 +/- 3.6 A in diameter (6 A larger than the original lipoproteins); they had a markedly decreased intrinsic protein fluorescence, a red-shifted fluorescence wavelength maximum, and more fluid lipid domains. These results indicate that the direct addition of excess lipids from membranes or other lipoproteins is a possible mechanism for lipid transfer to high density lipoproteins. Also they suggest a structural flexibility of high density lipoproteins that allows the addition of significant amounts of surface components.
Highlights
The interaction of sonicated, small vesicles of egg phosphatidylcholineand cholesterol(2:1, mol/mol) with bovine high density serum lipoproteins was examined in terms of lipid transfer between both types of particles and the resulting changes in lipoprotein structure
Since erythrocyte membranes are at equilibrium with plasma, the interaction between the cells and lipoproteins appears to be a simple exchange of lipids; when the exchangeable lipid contents of one of the particles is changed, net lipid transfer can occur [6].the interaction between high density serum lipoproteins (HDL) and cell membranes may result in lipid exchange or transfer in either direction depending on the relative affinities of the lipid for both particles and on lipid contents of the particles
The bulk of free bovine apolipoprotein A-1eluted eight fractions later than equilibrated HDL; apolipoprotein A-I was sufficiently well resolved to be detectable as a separate peak or a shoulder if present in our HDL preparations
Summary
The interaction of sonicated, small vesicles of egg phosphatidylcholineand cholesterol(2:1, mol/mol) with bovine high density serum lipoproteins was examined in terms of lipid transfer between both types of particles and the resulting changes in lipoprotein structure. The lipoproteins enriched in lipid were relatively uniform, spherical particles, 110 f 3.6 A in diameter (6 A larger than the original lipoproteins);they had a markedly decreased intrinsic protein fluorescence, a red-shifted fluorescencewavelength maximum,and more fluid lipid domains. These results indicate that the direct addition of excess lipids from membranes or other lipoproteins is a possible mechanism for lipid transfer to high density lipoproteins. T h e present observations may be relevant to the mode of lipid uptake by HDL from cell membranes ( 1-6) and from triglyceride-rich lipoproteins during lipolysis [9, 10]
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