The essential role of Factor VIII:C (FVIII:C, anti-hemophilia factor A) as a cofactor for Factor IXa-dependent activation of Factor X has been established. In this paper, we describe that capillary endothelial cells from bovine adrenal medulla express active FVIII:C gene. Accumulation of FVIII:C in conditioned media from an 8-day-old culture is approximately twice as high as that stored in the cell when immunoprecipitated FVIII:C was analyzed for its ability to convert Factor X to Factor Xa. Analysis of [35S]methionine-labeled and immunoprecipitated FVIII:C from cells or conditioned media on SDS-PAGE under fully denatured conditions indicated that the newly synthesized FVIII:C consists of heavy chain of M r 200,000 and light chain of M r 46,000. The secreted FVIII:C in the non-reduced condition however, has a molecular weight of 270,000 which suggests that in native protein, the heavy and light chains are held together by S-S bonds. Furthermore, susceptibility of the immunoprecipitated FVIII:C to N-glycanase digestion establishes that the endothelial cells derived FVIII:C contains asparagine-linked carbohydrate side chains.
