MECHANISM OF TRANSFER OF LDL-DERIVED FREE-CHOLESTEROL TO HDL SUBFRACTIONS IN HUMAN PLASMA

The transfer of [3H]cholesterol in low-density lipoprotein (LDL) to different high-density lipoprotein (HDL) species in native human plasma was determined by using nondenaturing two-dimensional electrophoresis. Transfer from LDL had a t1/2 at 37 °C of 51 ± 8 min and an activation energy of 18.0 kCal mol−1. There was unexpected specificity among HDL species as acceptors of LDL-derived labeled cholesterol. The largest fraction of the major α-migrating class (HDL2b) was the major initial acceptor of LDL-derived cholesterol. Kinetic analysis indicated a rapid secondary transfer from HDL2b to smaller αHDL (particularly HDL3) driven enzymatically by the lecithin–cholesterol acyltransferase reaction. Rates of transfer among αHDL were most rapid from the largest αHDL fraction (HDL2b), suggesting possible protein-mediated facilitation. Simultaneous measurements of the transport of LDL-derived and cell-derived isotopic cholesterol indicated that the former preferably utilized the αHDL pathway, with little label in pre-βHDL. The same experiments confirmed earlier data [Castro, G. R., & Fielding, C. J. (1988) Biochemistry 27, 25-29] that cell-derived cholesterol is preferentially channeled through pre-βHDL. We suggest that the functional heterogeneity of HDL demonstrated here includes the ability to independently process cell- and LDL-derived free cholesterol. © 1990, American Chemical Society. All rights reserved.