Catabolism of desialylated ceruloplasmin in the liver.

When desialylated ceruloplasmin (ASCPN), labeled with 64Cu and with 3H in its galactose residues, is injected intravenously into a rat, more than half of the radioactivity can be recovered within minutes in ASCPN precipitated immunochemically from liver homogenates. Both radioautographic studies and measurements of hepatic uptake of ASCPN following blockade of the reticuloendothelial system indicate that ASCPN enters only hepatocytes. Serial measurements on the immunoprecipitated ASCPN indicate that cleavage of 64Cu is 80% complete within 30 min of injection, whereas galactose is split from the protein even faster. Sucrose gradient fractionation of liver homogenates from rats treated with Triton WR 1339 or dextran reveals the principal site of the catabolic cleavage of copper and galactose to be lysosomes.