Lipid composition and cholesterol esterification in serum lipoprotein fraction of the horse, Equus caballus.

1. Changes in lipid components of lipoproteins during incubation of horse serum at 37 degrees C were investigated. In non-incubated serum, cholesterol and lecithin existed predominantly in alpha-lipoprotein or in high-density lipoprotein (HDL). Lysolecithin was mainly associated with the fraction with density above 1.21. 2. When serum was separated into alpha- and beta-lipoproteins by the heparin precipitation method after 1 hr incubation, the decrease in alpha-lipoprotein free cholesterol and lecithin was about four times that in beta-lipoprotein counterparts. 3. When serum lipoproteins were separated by ultracentrifugation, the decrease in each lipoprotein free cholesterol was closely paralleled with that in lecithin. 4. HDL appeared to be a preferential substrate for the lecithin: cholesterol acyltransferase reaction. 5. Disc electrophoretic patterns indicated significant differences in the composition of horse serum lipoproteins from those of human and rat.