SDS-PAGE analysis of the expression of WT FV and the Ala221Val FV variant. COS 1 cells expressing WT FV or Ala221Val:FV were depleted for Cys/Met and then radiolabeled with [³⁵S]Met/Cys for 30 minutes. After increasing time the radiolabeled FV in cell lysates and media were immunoprecipitated and electrophoresed on 7.5% SDS–polyacrylamide gels under reducing conditions (A). The radioactivity of the FV bands was analyzed with a Phosphorimager. To quantify the secretion profiles of WT (▪) and Ala221Val (□), the radioactivity of the FV-specific bands from cell lysate (B) and medium (C) was measured. The amount of radioactive FV in the cell lysate at 0 hours was assigned to be 100% for each FV variant. Each data point represents the mean of 3 independent experiments. Error bars represent ± SDs.