Studies of the interaction between apolipoproteins A and C and triacylglycerol-rich particles

We studied the interaction of apolipoproteins A-I, C, and HDL2 with phospholipid-stabilized, triacylglycerol-rich particles to learn more about the molecular mechanisms that underlie the metabolism of chylomicrons. Apolipoproteins A-I, C-I, C-III1 and C-III2 all bound to and destabilized triacylglycerol-rich particles, apparently by removing phospholipids from the particle surface. None of the apolipoprotein C tested, at any concentration, was, however, able to equal the disruptive effect of apolipoprotein A-I. The destabilizing effects of apolipoproteins A-I and C were not additive. Apolipoprotein C-III1 seemed to lessen the disruptive effect of apolipoprotein A-I by binding competitively to triacylglycerol-rich particles. Unexpectedly, previous binding of apolipoprotein A-I to triacylglycerol-rich particles nearly tripled the ability of these particles to bind apolipoprotein C. Destabilization of triacylglycerol-rich particles by apolipoprotein A-I was prevented by HDL2. The protective effect of HDL2 seemed to depend partly on transfer of unesterified cholesterol from HDL2, since the amounts of unesterified cholesterol and apolipoprotein A-I bound to the particles surface showed a strong negative correlation.