COMPARISON OF CARBOHYDRATE STRUCTURES OF SERUM ALPHA-FETOPROTEIN BY SEQUENTIAL GLYCOSIDASE DIGESTION AND LECTIN AFFINITY ELECTROPHORESIS

Serum alpha-fetoprotein (AFP) is a glycoprotein of which the sugar cha in is considered to show structural changes with malignancies. Microhe terogeneity of the serum AFP carbohydrate structure was studied in sam ples from 35 patients with benign and malignant diseases. Sera were di gested directly, extensively, and sequentially with sialidase, beta-ga lactosidase and beta-N-acetylhexosaminidase. Before and after digestio n, sera were examined by means of lectin affinity electrophoresis usin g eight lectins. Relationships between AFP carbohydrate structures and liver diseases were elucidated by the lectin-reactive profiles and th e effect of glycosidase digestion. More than 94% of the AFP carbohydra te structures found in patients with benign and malignant liver diseas es were biantennary complex-type oligosaccharides. Changes in the AFP carbohydrate structures al the early stage of hepatocellular carcinoma revealed the addition of alpha 1-6 fucose to the reducing terminal N- acetylglucosamine and monosialylated AFPs. In both advanced hepatocell ular carcinoma and AFP producing extrahepatic malignancies, AFP carboh ydrate structures were characterized as the further addition of beta 1 -4 N-acetylglucosamine and heterogeneity in the galactose and N-acetyl glucosamine residues. Sequential glycosidase digestion and lectin affi nity electrophoresis is useful for analysing the carbohydrate structur es of serum glycoprotein.