Increase of electrophoretic mobility and of content of soluble proteins of human plasma beta-lipoproteins by incubation of plasma in vitro.

Incubation of human plasma at 37 degrees C was shown to induce an increase in the electrophoretic mobility of beta-lipoproteins. beta-Lipoproteins were isolated by density gradient ultracentrifugation after such incubation and their composition was analysed. Incubation decreased the content of free cholesterol and increased that of soluble apolipoproteins. The soluble peptides appearing in LDL upon incubation showed 3 major and 2 minor bands upon polyacrylamide disc gel electrophoresis. Two of the major bands corresponded to apolipoprotein C-III-1 and C-III-2 and one of the minor to apolipoprotein C-II. The addition of an inhibitor to lecithin:cholesterol acyltransferase (LCAT) abolished the increase in electrophoretic mobility and to a large extent diminished the other reported effects of incubation. The hypothesis is put forward that during incubation of plasma at 37 degrees C the free cholesterol in the surface of LDL is removed through the action of LCAT, lipid transferases and exchange processes and is replaced in the surface shell by peptides which cause the change in electrophoretic mobility.