J. Biol. Chem., Vol. 261, Issue 25, 11631-11638, 09, 1986
The effects of liposome-reconstituted apolipoproteins on the binding of rat intermediate density lipoproteins to rat liver membranes
L Brissette, PD Roach and SP Noel
Rat intermediate density lipoproteins (IDL) bind specifically to high and
low affinity binding sites on rat liver membranes. In a recent paper
(Brissette, L., and Noel, S.-P. (1986) J. Biol. Chem. 261, 6847- 6852), we
have demonstrated that human low density lipoproteins and high density
lipoproteins-3 can totally prevent the specific binding of rat IDL to the
low affinity binding sites. The aim of the present studies was to determine
the effects of apoA-I, apoC, and apoE, reconstituted into liposomes, on the
binding of rat iodinated IDL to rat liver membranes. We found that a 50-,
100-, or 300-fold excess of liposome-reconstituted apoE, apoC, or apoA-I,
respectively, abolished the specific binding of IDL to the low affinity
binding sites. Only apoE liposomes had an effect on the high affinity
component; at a 100- fold excess no specific binding of IDL could be
detected. Liposomes by themselves or associated with erythrocyte membrane
proteins had virtually no effect on the binding of IDL. Taken together our
results suggest that apoE is the only ligand that can compete efficiently
for the sites that bind rat IDL with a high affinity. These sites may be
the expression of both the remnant and the LDL receptors. The binding to
the low affinity component probably represents weak interactions between
IDL and "unspecified-lipoprotein binding sites," which can be entirely
masked by human low density lipoproteins, high density lipoproteins-3, or
liposome-reconstituted apoA-I, apoE, or apoC at appropriate concentrations.
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