title: Kinetics of transfer of alpha-tocopherol between model and native plasma lipoproteins.
abstract: The rate of spontaneous transfer of alpha-tocopherol, cholesterol and beta-carotene between model and native lipoproteins was measured to determine the mechanism and kinetics of equilibration of these lipids in plasma. Cholesterol and alpha-tocopherol transfer from apolipoprotein A-I/1-palmityl-2- oleoylphosphatidylcholine ( POPC ) recombinants to bovine brain ganglioside/ POPC single bilage vesicles with half-times of approximately 20 min and 70 min, respectively. Under identical conditions, there is no significant transfer of beta-carotene even after an 18-h incubation period. alpha-Tocopherol transfers from apolipoprotein A-II/dimyristoylphosphatidylcholine recombinants with a half-time of 40 min and an activation energy of 17.2 kcal/mol. Incubation of high-density lipoproteins containing alpha-[3H]tocopherol with low-density lipoproteins or very-low-density lipoproteins results in the equilibration of the labelled lipid between the lipoprotein classes in 1 h. A comparison of the rates of transfer indicates that alpha-tocopherol equilibrates 2-3-times more slowly than cholesterol but on a time scale much shorter than the lifetime of lipoproteins in the circulation. Thus, the distribution of alpha-tocopherol is not kinetically controlled but determined thermodynamically by the partitioning between the total amount of lipid in each compartment. The spontaneous transfer of beta-carotene is too slow for this equilibration to occur.
mesh_terms: D016632:Apolipoprotein A-I; D016633:Apolipoprotein A-II; D001053:Apolipoproteins / Q000378:metabolism; D002338:Carotenoids / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism; D005732:Gangliosides / Q000378:metabolism; D008074:Lipoproteins / Q000378:metabolism*; D008075:Lipoproteins, HDL / Q000378:metabolism; D008077:Lipoproteins, LDL / Q000378:metabolism; D010713:Phosphatidylcholines / Q000378:metabolism; D014810:Vitamin E / Q000378:metabolism*
chemical_list: D016632:Apolipoprotein A-I; D016633:Apolipoprotein A-II; D001053:Apolipoproteins; D005732:Gangliosides; D008074:Lipoproteins; D008075:Lipoproteins, HDL; D008077:Lipoproteins, LDL; D010713:Phosphatidylcholines; D014810:Vitamin E; D002338:Carotenoids; D002784:Cholesterol