Detection and characterization of anionic polypeptidic fraction binding sites in rat liver plasma membranes and cultured hepatocytes

Abstract

The binding of human 125I-labeled ‘anionic polypeptidic fraction’ (APF) to purified rat liver plasma membranes was studied. The dissociation constant for this binding was 3.0 μg protein/mg membrane protein. Binding was competitively inhibited by unlabeled human APF, but not by human LDL (low density lipoproteins). When unlabeled HDL 3 was added, binding of labeled APF was competitively reduced to a level between that of unlabeled APF and unlabeled LDL. Experiments with cultured rat hepatocytes confirmed those obtained with liver membranes and suggested the presence in rat liver of saturable APF-binding sites which seem to be specific for APF. The physiologic significance of these APF binding sites is discussed in relation to the fate of cholesterol in the liver.