In suspensions of freshly isolated hepatocytes, asialotransferrin type 3 became rapidly bound by the asialoglycoprotein-binding hepatic lectin. Suspended hepatocytes, just as the liver of intact animals, catabolized asialotransferrin in a concentration-dependent manner. At low asialotransferrin concentrations (0.4-1 nM), the fraction of labeled protein degraded was much smaller than found with comparable concentrations of asialofetuin in an earlier study (Tolleshaug, H., Berg, T., Nilsson, M.,

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... nd Norum, K. R. (1977) Biochim. Biophys. Acta 499, 73-84). The fraction of endocytosed asialotransferrin that was degraded, could, however, be substantially increased by raising the concentration of asialotransferrin the medium. Release studies using a chelating agent or competitive inhibitors of the binding reaction showed that at low asialotransferrin concentrations, hepatocytes exocytose the preponderance of the intracellular asialotransferrin with a half-life of approximately 20 min. This novel observation raises the possibility that lysosomal homing of an endosome transporting asialoglycoprotein requires an intracellular target signal.