Binding, internalization, and degradation of AMP aminohydrolase by avian hepatocyte monolayers

Chicken muscle AMP aminohydrolase is cleared from the circulation of chickens after intravenous injection of the purified enzyme with a half-life of 3-5 min (Husic, H.D., and Suelter, C.H. (1980) Biochem. Biophys. Res. Commun. 95, 228-235). The enzyme is not inactivated before clearance, the clearance is inhibited by sulfated polysaccharides, and the enzyme is cleared primarily by the spleen and the parenchymal cells of the liver where it is internalized and degraded in lysosomes (Husic, H.D., and Suelter, C.H. (1984) J. Biol. Chem. 259, 4359-4364). The binding of AMP aminohydrolase to hepatocyte monolayers in vitro at 4 degrees C is saturable with a dissociation constant of 11.3 X 10(-8) M; there are 2.6 X 10(6) AMP aminohydrolase binding sites/hepatocyte. The interaction of the enzyme with hepatocyte monolayers is inhibited by sulfated polysaccharides, effectors of its enzymatic activity and high salt concentrations; various monosaccharides had little effect on the binding of the enzyme to hepatocyte monolayers. Heparitinase treatment of hepatocyte monolayers abolished 77% of the binding of the enzyme. Heparin promotes the dissociation of 125I-labeled or [14C]sucrose-labeled enzyme bound to the cell surface; radioactivity which is not dissociated by heparin is assumed to be internalized at 37 degrees C. Low molecular weight 125I-labeled degradation products are released into the media with time when the 125I-labeled enzyme, bound to hepatocytes at 4 degrees C, is incubated at 37 degrees C; when [14C]sucrose-labeled enzyme is incubated with hepatocytes at 37 degrees C, low molecular weight 14C-labeled degradation products are not released into the media but instead accumulate in the cells. The half-life for internalization of the bound enzyme based on this rate of accumulation is 0.77 h. These results suggest that glycosaminoglycans are involved in the binding of AMP aminohydrolase to the hepatocyte cell surface and that the bound enzyme is internalized and degraded.