IDENTIFICATION OF ALPHA-FETOPROTEIN-P4 SUGAR CHAIN AS ALPHA-2-]6 MONOSIALYLATED BIANTENNARY COMPLEX-TYPE OLIGOSACCHARIDES WITH AN EXPOSED GALACTOSE ON THE MANNOSE ALPHA-1-]6 ARM BY 2-DIMENSIONAL EXTENDED AGAROSE GEL-LECTIN AFFINITY ELECTROPHORESIS

Erythroagglutinating phytohemagglutinin (E-PHA)-reactive alpha-fetopro tein (AFP)-P4 and E-PHA weakly-reactive AFP-P3 of sera from cord blood at term and from patients with hepatocellular carcinomas showed a mob ility of monosialo-AFP in two-dimensional extended agarose gel-E-PHA a ffinity electrophoresis. Asialo-AFP had as high an affinity for E-PHA as that of monosialo-AFP-P4, while disialo-AFP, AFP-P2, revealed a neg ligible affinity for E-PHA. For Allomyrina dichotoma lectin (allo A), asialo-AFP had no affinity with a mobility of AFP-Als, monosialo-AFP-P 4 had the highest affinity with a mobility of AFP-A3, and monosialo-AF P-P3 had an intermediate affinity with a mobility of AFP-A2s. The affi nity of AFP-P4 for E-PHA was reduced by galactosidase digestion, indic ating the presence of galactose residues, one sialylated and the other exposed. From the known high affinity of E-PHA for biantennary comple x-type oligosaccharides with a terminal beta 1-->4 galactose of the Ma n alpha 1-->6 antenna and from that of allo A for an alpha 2-->6 sialy lated beta 1-->4 galactose of the Man alpha1-->3 antenna, together wit h the nonbisected biantennary structure of AFP-P4 as deduced from its high affinity for concanavalin A, the sugar chain structure of AFP-P4, which increases frequently in hepatocellular carcinomas, was identifi ed as alpha 2-->6 monosialylated nonbisected biantennary complex-type oligosaccharides with an exposed beta 1-->4 galactose of the Man alpha 1-->6 arm and with or without fucosylated core N-acetylglucosamine, a nd AFP-P3 as similar oligosaccharides with an exposed beta 1-->4 galac tose of the Man alpha 2-->3 arm.