Interaction between apo A-I-containing lipoproteins and lecithin:cholesterol acyltransferase.
HDL2 and HDL3 subfractions of two species of apo A-I-containing lipoprotein, one containing only apo A-I (LpA-I) and the other containing both apo A-I and apo A-II (LpA-I/A-II), were tested for reactivity to lecithin:cholesterol acyltransferase (LCAT). These subfractions and their mixtures were incubated with lipoprotein-deficient plasma (LCAT source), and the rate of cholesterol esterification and kinetic parameters were determined. Apparent Vmax (appVmax) and apparent Km (appKm) for HDL2 subfractions of LpA-I and LpA-I/A-II were significantly lower than those of their HDL3 counterparts. Differences between subfractions were much more prominent in LpA-I than in LpA-I/A-II. appVmax of the HDL2 subfraction of LpA-I (LpA-IHDL2) was one-fifth, and appKm was one-third of those for the HDL3 subfraction (LpA-IHDL3). appVmax and appKm of LpA-IHDL2 were both lowest among the apo A-I-containing lipoprotein subfractions. When LpA-IHDL2 was added to other subfractions, the molar rate of cholesterol esterification was suppressed. Since LpA-IHDL2 consists of a particle 11.1 nm in diameter, our observations suggest that LpA-IHDL2 suppresses cholesterol esterification in apo A-I-containing lipoprotein, possibly by displacing LCAT from other subfractions with higher appKm and higher appVmax to 11.1 nm LpA-I particles with lower appKm and lower appVmax. All of these data suggest that the relative amount of 11.1 nm LpA-I particles in plasma regulates the reactivity of apo A-I-containing lipoprotein to LCAT and may play a key role on the production of cholesteryl esters in plasma.
Ikeda
Y
Y
Department of Pediatrics, Kumamoto University School of Medicine, Kumamoto, Japan.
Ohta
T
T
Matsuda
I
I
D016632:Apolipoprotein A-I / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D005591:Chemical Fractionation; D002788:Cholesterol Esters / Q000097:blood; D004789:Enzyme Activation; D006801:Humans; D007700:Kinetics; D008074:Lipoproteins / Q000737:chemistry; D007862:Phosphatidylcholine-Sterol O-Acyltransferase / Q000378:metabolism*; D013379:Substrate Specificity
D016632:Apolipoprotein A-I; D002788:Cholesterol Esters; D008074:Lipoproteins; D007862:Phosphatidylcholine-Sterol O-Acyltransferase