Functional size of the human asialoglycoprotein receptor as determined by radiation inactivation

The radiation target size of the functional asialoglycoprotein receptor (ASGP-R) in purified plasma membranes was determined for human liver and the human hepatoma cell line, Hep G2, by evaluation of the binding of ¹²⁵I-asialoorosomucoid. Identical inactivation curves were observed for ASGP-R from normal human liver and post-mortem human liver and exhibited a functional unit of 70,000 daltons. The human hepatoma Hep G2 ASGP-R, in contrast, showed a target size of 140,000 daltons. These results suggest that the functional ligand-binding unit of the human ASGP-R is a multimer of the ~ 34,000-dalton unglycosylated receptor polypeptide (Schwartz, A.L, and Rup, D. (1983) J. Biol. Chem. 258, 11249-11255).