Lipoprotein substrates for plasma cholesterol esterification. Influence of particle size and composition of the high density lipoprotein subfraction 3.

Subpopulations of lipoproteins within the high density lipoprotein subfraction 3 (HDL3) have been isolated from human plasma and characterized in terms of their chemical composition and particle size. Since HDL3 are the major substrates for the esterification of plasma cholesterol, and thus play a central role in the transport of cholesterol through the plasma, these studies also examined the relative capacities of different HDL3 subpopulations to interact with lecithin: cholesterol acyltransferase. Substrate reactivity of a given preparation of lipoproteins was defined in terms of the Vmax of the cholesterol esterification reaction in incubations containing a fixed amount of human lipoprotein-free plasma as a source of the enzyme. Substrate reactivity was found to correlate inversely with the radius of HDL3 particles. This inverse relationship between particle size and substrate reactivity was independent of the particle content of cholesteryl ester.