Human placental coated vesicles contain receptor-bound transferrin

Abstract

Human placental coated vesicles were purified by a method involving sucrose density-gradient centrifugation and treatment with wheat-germ agglutinin. These preparations were free of contamination by placental microvillus fragments. Crossed immunoelectrophoresis demonstrated that the coated vesicles contained a single serum protein, identified as transferrin. This transferrin was observed only after the vesicles were treated with a non-ionic detergent, and its behavior during crossed hydrophobic-interaction immunoelectrophoresis suggested that a large proportion of it was receptor-bound. No other serum proteins, including IgG, could be detected in these preparations. Receptor-bound transferrin was the only antigen common to placental coated vesicles and microvilli, implying that other plasma membrane proteins are excluded from the region of membrane involved in coated vesicle formation.