[Microheterogeneity of alpha-fetoprotein in the amniotic fluid--developmental changes in the molecular structure of...

By means of lectin affinity crossed-line immunoelectrophoresis, microheterogeneity of alpha-fetoprotein (AFP) was studied in 41 amniotic fluid samples between 41 to 287 days of gestation. Microheterogeneity was assessed by the structural differences in the carbohydrate chain identified by the specific binding between oligosaccharide molecule(s) and certain lectins such as concanavalin A, Lens culinaris hemagglutinin, phytohemagglutinin E or Ricinus communis agglutinin I. It was found that four carbohydrate chains were identifiable at an early stage of gestation; (1) mannose (Man).core type, (2) bisecting N-acetylglucosamine (GlcNAc) type, (3) fucose (Fuc) type, and fucosyl-bisecting GlcNAc type. A carbohydrate chain with both bisecting GlcNAc and Fuc was found only at an early stage of of gestation. A carbohydrate chain with either bisecting GlcNAc or Fuc also decreased with fetal growth, and AFP at the end stage of gestation was composed mainly of Man.core type carbohydrate chain. The addition or removal of the oligosaccharide molecule takes place at the Goldi complex subjected to various modifications by the glycosylation enzyme, and the present findings indicate that a certain enzyme (s) for the processing of oligosaccharide differs according to the developmental change in AFP-producing sites or the maturation of AFP-producing cells, and such is responsible for the different AFP carbohydrate chains in the amniotic fluid at different gestational stages.