Multiple molecular forms of endothelial cell factor VIII related antigen

Heterogeneous factor VIII related antigen isolated from endothelial cell postculture medium was characterized. On crossed immunoelectrophoresis, slow moving less anodal populations of factor VIII related antigen molecules were more prominent in endothelial cell postculture medium than in plasma. The protein synthesized by endothelial cells appeared as two discrete protein bands of different molecular weight in sodium dodecyl sulfate polyacrylamide gels. In contrast the factor VIII related antigen isolated from plasma moved as a single protein band in an identical gel system. The factor VIII related antigen from endothelial cell postculture medium was immunoisolated using monospecific rabbit antibody to normal human plasma factor VIII related antigen, electrophoresed on sodium dodecyl sulfate polyacrylamide gels, radiolabeled with 125I, trypsinized and subjected to peptide mapping using two-dimensional high voltage electrophoresis and thin-layer chromatography. The two forms of endothelial cell factor VIII antigen had virtually identical peptide maps. These studies suggest that the molecular heterogeneity of the factor VIII related antigen system reflects polymeric associations of identical subunits. Circulation in vivo may alter the ratio of polymer subsets.