Serum inhibitors of desialylated glycoprotein binding to hepatocyte membranes

Abstract

Identification of the material present in human serum which is responsible for inhibition of binding of desialylated glycoproteins to rat hepatocyte membranes was accomplished by means of affinity chromatrography using Sephadex to which the galactose-specific lectin, Ricinus Communis Agglutinin (RCA 1) was covalently bound. RCA 1-Sephadex was capable of extraction of virtually all of the inhibitory activity from cirrhotic serum. The RCA 1-bound inhibitory activity could be eluted with 0.05 M d-galactose. The d-galactose eluate when subjected to radioimmunoelectrophoresis against a number of a specific antibodies to human serum glycoproteins produced arcs corresponding to α 1-acid glycoprotein, α 2-macroglobulin, IgG, IgA, and IgM. In another experiment putative terminal galactosyl groups of desialylated glycoproteins in the d-galactose eluate from cirrhotic serum exposed to RCA 1-Sephadex were labelled with tritiated borohydride after treatment with galactose oxidase. Subsequent gel electrophoresis showed peaks of radioactivity throughout the area of the gel corresponding to protein molecular weights of the 19 S, 7 S, and 4 S classes. It thus appears that a heterogeneous population of desialylated serum glycoproteins accounts for the inhibition of binding of desialylated glycoprotein to the hepatocyte membrane and that these desialylated glycoproteins are present in small amounts in normal human serum and in greatly increased quanitities in serum from patients with cirrhosis.