Inhibition of the binding of low density lipoproteins to liver membrane receptors by rat serum phosphorylcholine binding protein.

Rat serum phosphorylcholine binding protein (PCBP) is characterized by its Ca2+ dependent property to bind phosphorylcholine ligand. PCBP immobilized on sepharose has been shown to selectively bind human plasma apo B and E containing lipoproteins. The present report describes an inhibitory effect of PCBP on the binding of human 125I-LDL to LDL receptors on estradiol treated rat liver membranes. Pre-incubation of liver membranes with PCBP did not affect the binding of 125I-LDL to the membranes. Gel filtration analysis of the incubation products from the LDL-receptor assay showed a concentration dependent binding of 125I-PCBP to LDL. The inhibitory effect of PCBP is likely due to the formation of LDL-PCBP complex and not due to the binding of PCBP to the LDL receptor site.