Expression levels of the recombinant FV variants. COS 1 cells expressing the WT, Ala221Val, Ala221Gly, Glu275Gln, and Cys220Ala/Cys301Ala FV variants were transiently transfected, and the expression levels of FV in the culture media after 72 hours were measured by ELISA. The histograms and bars represent the means ± SEMs (n = 6). The mean value of WT FV was 200 ng/μL and is assigned as 100% in the figure.