Binding and endocytosis of glycoproteins and neoglycoproteins by isolated rabbit hepatocytes

Rabbit hepatocytes were isolated by a collagenase technique, and used to study the binding and endocytosis of the glycoprotein, asialo-orosomucoid, and the neoglycoprotein, Gal₃₉-bovine serum albumin. Both of these proteins contain exposed galactosyl residues, and were avidly bound by the lectin on the hepatic parenchymal cell surface. Steady state and kinetic experiments performed at 2°C and at 37°C revealed the presence of two apparent classes of binding sites totalling 4.7 x 10⁵ sites/cell at 2°C, and 6.3 x 10⁵-sites/cell at 37°C. At 37°C, both classes of sites participated in internalization of bound ligand. The cells were capable of internalizing about 60000 molecules/min per cell. The process appeared to be first-order, with a rate constant k = 0.098 min^-1 and t(1/2) = 7.1 ± 0.6 min. Binding could be inhibited by galactose-containing compounds, EGTA, and by anti-(hepatic lectin) immunoglobin G. The inhibition by antibody appeared to be reversible upon removal of antibody-containing medium.