Immunocytochemical identification of beta-protein precursor in cultured vascular cells

The immunocytochemical and immunochemical identification of beta-protein precursor in cultured vascular cells was undertaken using three types of antibodies to the synthetic predictive peptides (extracellular portion; 275-286, beta-protein portion; 597-620, C-terminal portion; 681-695) of beta-protein precursor. Monoclonal antibody directed toward the beta-protein portion stained the surface membrane of the cultured endothelial cells as well as cytoplasmic organelles. Immunoblotting of the subcellular fractions of the cell homogenate with three antibodies revealed that the plasma membrane associated beta-protein precursor consists of 105-130 kDa protein complexes and that the mitochondria-microsome-associated beta-protein consists of related 30-67 kDa protein complexes. The immunoreactivity of the protein bands was blocked by pretreating the monoclonal antibody with bovine serum albumin-conjugated beta-protein. These results indicate that the form of the beta-protein precursor or beta-protein-related components in cultured vascular cells is heterogeneous in terms of molecular size and subcellular localization.