Fate of receptor and ligand during endocytosis of asialoglycoproteins by isolated hepatocytes.

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Abstract
The endocytosis leading to degradation of 125I-labeled asialo-orosomucoid specifically bound to the surface of freshly isolated [rat] hepatocytes was monitored as a function of time at 37.degree. C. Experimental values were determined for the rates of internalization, dissociation of the receptor-ligand complex, and degradation of the labeled ligand. Compartmental analysis and computer modeling revealed that the data were compatible with dissociation of ligand from receptor preceding ligand degradation. The rate coefficient for internalization was calculated to be an order of magnitude greater than that for receptor-ligand dissociation. Ligand internalization did not result in concomitant depletion in the total number of cell surface receptors. Ligand probably remains associated with the receptor after internalization, the complex is dissociated prior to degradation, and new, unoccupied receptors are promptly returned to the cell surface from an internal pool.