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 degrees 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 alpha-migrating class (HDL2b) was the major initial acceptor of LDL-derived cholesterol. Kinetic analysis indicated a rapid secondary transfer from HDL2b to smaller alpha HDL (particularly HDL3) driven enzymatically by the lecithin-cholesterol acyltransferase reaction. Rates of transfer among alpha HDL were most rapid from the largest alpha HDL 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 alpha HDL pathway, with little label in pre-beta HDL. 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-beta HDL. We suggest that the functional heterogeneity of HDL demonstrated here includes the ability to independently process cell- and LDL-derived free cholesterol.
Miida
T
T
Cardiovascular Research Institute, University of California, San Francisco 94143.
Fielding
C J
CJ
Fielding
P E
PE
D002784:Cholesterol / Q000097:blood*; D015180:Electrophoresis, Gel, Two-Dimensional; D006801:Humans; D007700:Kinetics; D008075:Lipoproteins, HDL / Q000097:blood* / Q000302:isolation & purification; D008077:Lipoproteins, LDL / Q000097:blood* / Q000302:isolation & purification; D014316:Tritium
D008075:Lipoproteins, HDL; D008077:Lipoproteins, LDL; D014316:Tritium; D002784:Cholesterol