Membranes from rat liver were analysed under reducing conditions. The components of the soluble membranes responsible for the binding of acetylated low density lipoprotein (acetyl-LDL) and maleylated bovine serum albumin (Mal-BSA) were chromatographed on a polyethyleneimine-cellulose column and subsequently separated by gel electrophoresis. For both ligands a major binding protein (Mr = 35,000) was revealed by ligand blotting. A minor protein (Mr greater than 67,000) exhibited little binding. The Scatchard plot of the 131I-Mal-BSA binding data of the 35 kDa protein was linear, with a Kd of 17.3 nM. High concentrations of acetyl-LDL competed for half of the 131I-Mal-BSA binding. Excessive Mal-BSA competed for all the visible acetyl-LDL binding. The findings indicate the existence, in the reduced hepatic membrane, of a 35 kDa protein that has two binding sites for 131I-Mal-BSA and one binding site for acetyl-LDL.
