Characterization of E-PHA-reactive alpha-fetoprotein isoforms by two-dimensional lectin affinity electrophoresis.

Erythroagglutinating phytohemagglutinin (E-PHA)-dependent isoforms of human alpha-fetoprotein (AFP) from cord blood were analyzed for their carbohydrate structures by two-dimensional electrophoresis with E-PHA combined with extended agarose gel electrophoresis or with affinity electrophoresis with concanavalin A or Allomyrina dichtoma lectin. By means of neuraminidase and/or beta-galactosidase treatment, AFP-P2 was identified as alpha 2-->6 disialo-AFP, AFP-P3 as having biantennary structures with alpha 2-->6 monosialylated galactose of the Mannose (Man) alpha 1-->6 arm, AFP-P4 as having alpha 2-->6 monosialylated galactose of the Man alpha 1-->3 arm, and AFP-P5 as disialo-AFP with alpha 2-->3 sialylated galactose of the Man alpha 1-->6 antenna with the alpha 2-->6 sialylated galactose of the other antenna. Desialylated AFP with the terminal galactose of the Man alpha 1-->6 antenna with or without the galactose of the other arm also had a migration of AFP-P4, and other hydrolytic intermediates without the terminal galactose of the Man alpha 1-->6 arm with and without the galactose of the other antenna had mobilities of AFP-P3s and AFP-P3, respectively. Thus, the present system of two-dimensional lectin affinity electrophoreses would provide a model for the determination of the sugar chain structure of glycoproteins.